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Dynamic Attribution of Global Water Demand to Surface Water and Groundwater Resources: Effects of Abstractions and Return Flows on River Discharge
Abstract
As human water demand is increasing worldwide, pressure on available water resources grows and their sustainable exploitation is at risk. To mimic changes in exploitation intensity and the connecting feedbacks between surface water and groundwater systems, a dynamic attribution of demand to water resources is necessary. However, current global-scale hydrological models lack the ability to do so. This study explores the dynamic attribution of water demand to simulated water availability. It accounts for essential feedbacks, such as return flows of unconsumed water and riverbed infiltration. Results show that abstractions and feedbacks strongly affect water allocation over time, particularly in irrigated areas. Also residence time of water is affected, as shown by changes in low flow magnitude, frequency, and timing. The dynamic representation of abstractions and feedbacks makes the model a suitable tool for assessing spatial and temporal impacts of changing global water demand on hydrology and water resources.
... affecting infrastructure and increasing flood risks in coastal cities 1 . Last, declining groundwater levels reduce the groundwater discharge that is essential for sustaining river flows, lake levels, springs, groundwater-fed wetlands and related ecosystems, especially during droughts 12,13 . The net result is a slow desiccation of the landscape, with the progression largely hidden by precipitation variability. ...
... Unlike previous large-scale impact assessments of groundwater depletion 5,6 , we pay particular attention to the intricate effects of groundwater pumping on interactions between groundwater and surface water through groundwater discharge and river infiltration. For this assessment we used a physically based global-scale surface water-groundwater model [12][13][14][15] (GSGM; see Methods). We simulated groundwater heads and head-dependent groundwater fluxes globally at a high resolution. ...
... For surface elevation we used data from HydroSHEDS 23 and Hydro1k 32 . Model outcomes have been extensively validated against observed river discharges and heads, and additionally, in this study, to water table depths, fluctuations and declines, and timing of environmental flow limits, showing good results [12][13][14][15]30,31 (see Methods section 'Evaluation of simulated groundwater heads, head declines and trends'). ...
Groundwater is the world’s largest freshwater resource and is critically important for irrigation, and hence for global food security1,2,3. Already, unsustainable groundwater pumping exceeds recharge from precipitation and rivers⁴, leading to substantial drops in the levels of groundwater and losses of groundwater from its storage, especially in intensively irrigated regions5,6,7. When groundwater levels drop, discharges from groundwater to streams decline, reverse in direction or even stop completely, thereby decreasing streamflow, with potentially devastating effects on aquatic ecosystems. Here we link declines in the levels of groundwater that result from groundwater pumping to decreases in streamflow globally, and estimate where and when environmentally critical streamflows—which are required to maintain healthy ecosystems—will no longer be sustained. We estimate that, by 2050, environmental flow limits will be reached for approximately 42 to 79 per cent of the watersheds in which there is groundwater pumping worldwide, and that this will generally occur before substantial losses in groundwater storage are experienced. Only a small decline in groundwater level is needed to affect streamflow, making our estimates uncertain for streams near a transition to reversed groundwater discharge. However, for many areas, groundwater pumping rates are high and environmental flow limits are known to be severely exceeded. Compared to surface-water use, the effects of groundwater pumping are markedly delayed. Our results thus reveal the current and future environmental legacy of groundwater use.
... The dimensions of water use Before providing definitions and concepts about groundwater per se, it is good to first define the different dimensions of human water use, as it is excessive water use that ultimately results in the depletion of groundwater resources. Water use is a general term that encompasses water demand, water withdrawal and consumptive water use (Döll et al 2012, De Graaf et al 2014. ...
... diffuse recharge) and from surface water bodies such as ephemeral streams, wetlands or lakes (Scanlon et al 2006, Crosbie et al 2012, Taylor et al 2013. Modelled global estimates of diffuse recharge range from 11 000 to 17 000 km 3 yr −1 , equivalent to 30%-40% of the world's renewable freshwater resources (IGRAC GGIS, Döll and Fiedler 2008, Wada et al 2010, Wada and Heinrich 2013, De Graaf et al 2014, 2017, Hanasaki et al 2018. These modelled global recharge fluxes tend not to include focused recharge, which can be substantial in semi-arid environments, while preferential flow processes and the profound seasonality of recharge are equally underrepresented. ...
... Definition of water demand, water withdrawal, consumptive water use and return flow Döll et al (2012), De Graaf et al (2014) 2.2 Fossil groundwater, non-renewable groundwater and groundwater depletion Definition of fossil, young and modern groundwater; Age-depth relationship Broers (2004), Gleeson et al (2015), Jasechko et al (2017) Definition of non-renewable groundwater, groundwater depletion and groundwater mining Margat et al (2006), Margat and Van der Gun (2013) 2.3 Groundwater-surface water interaction and the sources of pumped groundwater ...
Population growth, economic development, and dietary changes have drastically increased the demand for food and water. The resulting expansion of irrigated agriculture into semi-arid areas with limited precipitation and surface water has greatly increased the dependence of irrigated crops on groundwater withdrawal. Also, the increasing number of people living in mega-cities without access to clean surface water or piped drinking water has drastically increased urban groundwater use. The result of these trends has been the steady increase of the use of non-renewable groundwater resources and associated high rates of aquifer depletion around the globe. We present a comprehensive review of the state-of-the-art in research on non-renewable groundwater use and groundwater depletion. We start with a section defining the concepts of non-renewable groundwater, fossil groundwater and groundwater depletion and place these concepts in a hydrogeological perspective. We pay particular attention to the interaction between groundwater withdrawal, recharge and surface water which is critical to understanding sustainable groundwater withdrawal. We provide an overview of methods that have been used to estimate groundwater depletion, followed by an extensive review of global and regional depletion estimates, the adverse impacts of groundwater depletion and the hydroeconomics of groundwater use. We end this review with an outlook for future research based on main research gaps and challenges identified. This review shows that both the estimates of current depletion rates and the future availability of non-renewable groundwater are highly uncertain and that considerable data and research challenges need to be overcome if we hope to reduce this uncertainty in the near future.
... Promoting irrigation efficiency often not only reduces withdrawals, but also decreases return flows. Changes in return flows link field hydrology to basin hydrology [24][25][26][27]. Therefore, it is important to undertake a basin-wide approach when it comes to increasing water-use efficiency. ...
... Therefore, it is important to undertake a basin-wide approach when it comes to increasing water-use efficiency. If surface irrigation systems are replaced by sprinkler or drip systems, the return flow decreases, which in turn reduces downstream water availability [10,28] and can amount to up to 60% (77% in rice fields) of the water applied for irrigation [27]. Cai et al. [29] used an integrated modeling approach which included hydrologic and agronomic models for the evaluation of basin management scenarios in the Maipo River Basin in Chile. ...
Increases in water demand often result in unsustainable water use, leaving insufficient amounts of water for the environment. Therefore, water-saving strategies have been introduced to the environmental policy agenda in many (semi)-arid regions. As many such interventions failed to reach their objectives, a comprehensive tool is needed to assess them. We introduced a constructive framework to assess the proposed strategies by estimating five key components of the water balance in an area: (1) Demand; (2) Availability; (3) Withdrawal; (4) Depletion and (5) Outflow. The framework was applied to assess the Urmia Lake Restoration Program (ULRP) which aimed to increase the basin outflow to the lake to reach 3.1 × 10 9 m 3 yr −1. Results suggested that ULRP could help to increase the Outflow by up to 57%. However, successful implementation of the ULRP was foreseen to be impeded because of three main reasons: (i) decreasing return flows; (ii) increased Depletion; (iii) the impact of climate change. Decreasing return flows and increasing Depletion were expected due to the introduction of technologies that increase irrigation efficiency, while climate change could decrease future water availability by an estimated 3-15%. We suggest that to reach the intervention target, strategies need to focus on reducing water depletion rather than water withdrawals. The framework can be used to comprehensively assess water-saving strategies, particularly in water-stressed basins.
... It is widely used for irrigation, drinking water, and industries (Döll et al., 2012;UNESCO, 2010;Wada et al., 2011). During times of droughts, groundwater acts as a natural buffer as it sustains groundwater flow to the river, supporting river low flows, groundwater-fed wetlands, and related ecosystems (de Graaf et al., 2014(de Graaf et al., , 2019 and shallow water tables maintaining evapotranspiration (Chang et al., 2018;Maxwell & Condon, 2016;Shrestha et al., 2018). Groundwater often flows across topographic and administrative boundaries at considerable rates, supporting water budgets of receiving catchments (Schaller & Fan, 2009). ...
... Groundwater often flows across topographic and administrative boundaries at considerable rates, supporting water budgets of receiving catchments (Schaller & Fan, 2009). With climate change and increasing human water demands, Despite the importance of groundwater and the explicit focus on groundwater recharge and groundwater pumping in global-scale studies (e.g., de Graaf et al., 2014;Döll et al., 2012), most global-scale hydrological models do not simulate groundwater flow. The main reason for this omission is the lack of consistent globally available hydrogeological data that are required for a realistic physical representation of the groundwater system (Gleeson et al., 2014), enabling the simulation of groundwater head dynamics, lateral flows, and the effect of storage changes, be it from climate or groundwater pumping. ...
Groundwater is the world's most important freshwater resource. Despite this importance, groundwater flow and interactions between groundwater and other parts of the hydrological cycle are often neglected or simplified in large‐scale hydrological models. One of the challenges in simulating groundwater flow and continental to global scales is the lack of consistent globally available hydrogeological data. These input data are needed for a more realistic physical representation of the groundwater system, enabling the simulation of groundwater head dynamics and lateral flows. A realistic representation of the subsurface is especially important as large‐scale hydrological models move to finer resolutions and aim to provide accurate and locally relevant hydrologic information everywhere. In this study, we aim at improving and extending on current available large‐scale data sets providing information of the subsurface. We present a detailed aquifer representation for the continental United States and Canada at hyper resolution (250 × 250 m). We integrate local hydrogeological information, including observations of aquifer layer thickness, conductivity, and vertical structure, to obtain representative aquifer parameter values applicable to the continental scale. The methods used are simple and can be expanded to other parts of the world. Hydrological simulations were performed using the integrated hydrological model ParFlow and demonstrated improved model performance when using the new aquifer parameterization. Our results support that more detailed and accurate aquifer parameterization will advance our understanding of the groundwater system at larger scales.
... One motivation in developing coupled atmospheric and hydrological models is to improve parameterization schemes for water cycling processes, and then enhance simulating and forecasting accuracy. Some human activities, e.g., reservoir impounding and regulation, groundwater extraction and irrigation, can significantly alter hydrological processes and the water cycle [98][99][100][101][102][103]. The interactions and feedbacks between anthropogenic activities and hydrometeorological processes have been one of the frontier fields of scientific water research. ...
The past two decades have seen an intensive development in two-way coupled atmospheric and hydrological models, providing new opportunities to thoroughly understand hydrology–atmosphere coupling and improve hydrometeorological forecasting, which has not been possible before. This paper summarizes recent developments in hydrological presentation in land surface models (LSMs) and climate models, and the two-way coupling of atmospheric and hydrological models. The fully coupled models have been widely applied in identifying the impact of lateral surface and subsurface water transport in a land–atmosphere coupled system, and hydrometeorological simulations using techniques such as parameter calibration, data assimilation, and hydrology model structure revision have been used to improve the model accuracy. However, their applications still face major challenges, e.g., the complexity of hydrological parameter calibration, the lack of understanding of the physical mechanisms at high resolution, the parameterization of anthropogenic activities, and the limitations in simulation domain and period. Despite these difficulties, fully coupled atmospheric and hydrological models will gradually evolve into powerful tools to reproduce regional water cycles, offering significant potential for scientifically investigating water resources security issues affected by both climate change and human activities.
... According to the consumption type, including irrigation and urban, and the location of observation and pumping wells, polygons are drawn in the GMS model and an initial value as recharge rate is considered for each one. In the Zanjan aquifer, the return flows of unconsumed abstracted water is 20% for agriculture and 80% for urban and industrial uses, indicating that these proportions of (Jafari et al. 2012;De Graaf et al. 2014). Also, in order to specify the impacts of direct rainfall, as the natural recharge, on the aquifer, the effective precipitation (the period when rainfall rate exceeds evaporation rate) was taken into account, and the measured precipitation rate calculated by rainfall stations in the study area in March 2008 was assigned to the model. ...
In the present study, simulation of groundwater resources of the Zanjan Plain aquifer located in the western part of Iran was done using the GMS 7.1 software to evaluate groundwater table changes and the concentration of physicochemical parameters. A new comprehension about groundwater quality changes was considered by evaluating the effects of size and sediment granulation as a hydrogeological factor on groundwater resources. Therefore, over a period of 3 years, between 2009 and 2012, a MODFLOW model was calibrated and hydrodynamic parameters were extracted that indicated higher hydraulic conductivity values in foothill areas due to coarse-grained alluvial materials as well as the effect of runoff within the Zanjan city on greater amount of recharge rate. The calculated flow budget also showed that from 2009 to 2012, on average, approximately 210 MCM of water resources decreased in the Zanjan aquifer every year. The results of the sensitivity analysis indicated that the changes in the recharge rate affected the model mostly. From 2012 to 2018, the process of validation was done and revealed that in the southeastern part of the aquifer the groundwater table diminished significantly due to the higher density of irrigated agricultural lands. The results of the MT3DMS model showed that although the amount of electrical conductivity (EC) and total hardness (TH) decreased during the period, the groundwater quality in the central and northwestern areas of the plain was still unsuitable. Additionally, the assessment of the changes in the amount of the mentioned parameters in comparison to the changes in groundwater level and the annual rainfall showed that because of coarse-grained alluvial sediments, groundwater quality was at the highest level in the foothill regions and deteriorated in the terrace areas of the aquifer due to greater dissolution of the fine-grained sediments, and in that the thalweg area of the plain, the groundwater quality increased because of the fine-grained sediments scour due to the Zanjanrood river.
... However, excessive groundwater abstraction has led to groundwater depletion and pollution and thus challenges water resources management in the country. These developments also have negative effects on the streamflow of groundwater fed rivers, the health of the ecosystems, and the depths of local groundwater tables (De Graaf et al. 2014). The complete drying up of Haramaya Lake in Eastern Ethiopia since 2005 is an example for the consequences of decreasing groundwater levels due to over-pumping of groundwater for agriculture and household use (Abebe et al. 2014). ...
... To create such a model, research on isotopic fractionation is necessary, first to trace changes in exploitation intensity and second to understand the interconnecting feedbacks between surface water and groundwater systems [14]. ...
The unique climate conditions and water source composition in the Tianshan Mountain provide a good experimental site for verifying the relationships between water resources and climate change on a larger scale. With the help of water isotopes (D, 18O), a more reliable conceptual model of groundwater systems can be constructed on both local and regional scales, especially in areas that are susceptible to climate change and under pressure from intensive human activities. In this paper, we present δ18O, δD, d-excess, RWLs and altitude effects of river water and groundwater based on the data derived from our network of stable isotope sampling sites along the Kaidu River. Stable isotope mass balance was applied to study the interactions between groundwater and surface water and to quantify the recharge proportions between bodies of water in typical regions. The results showed that the Kaidu River is composed of precipitation, ice and snow melt, baseflow and groundwater. The percentage of groundwater increased with the distance between upstream (the runoff producing area) and the leading edge of the glacier. The two recharge areas are the spring overflow from the mountain area to the alluvial layer of the inclined plain and the leading edge of the alluvial plains to areas with fine soil. The groundwater recharge ratio is about 23% in high mountain areas but 46% or more in the middle and lower reaches. These results generated a more comprehensive understanding of the hydrological cycle of inland rivers in arid regions.
... Around 30% of human-consumed water comes from aquatic ecosystems (rivers, lakes and wetlands) (UNESCO-UN Water 2020). Water abstraction from rivers and connected aquifers often results in impacts far beyond the point of abstraction (De Graaf et al. 2014). For example, abstraction in the lower Yangtze River (China) has led to reduced flows and salt intrusions in its estuary (Zhang et al. 2012). ...
The land–river interface (LRI) is important for sustainable development. The environmental processes that define the LRI support the natural capital and ecosystem services that are linked directly to multiple Sustainable Development Goals (SDGs). However, existing approaches to scale up or down SDG targets and link them to natural capital are insufficient for the two-way human–environment interactions that exist in the LRI. Therefore, this study proposes a place-based approach to interpret the SDG framework to support sustainable land/water management, by (i) identifying key priorities for sustainable development through a normative content analysis of the SDG targets, and (ii) illustrating these priorities and associated challenges within the LRI, based on a literature review and case-studies on human–environment interactions. The content analysis identifies three overarching sustainable development priorities: (i) ensuring improved access to resources and services provided by the LRI, (ii) strengthening the resilience of the LRI to deal with social and natural shocks, and (iii) increasing resource efficiency. The review of the current state of LRIs across the world confirms that these are indeed priority areas for sustainable development. Yet, the challenges of attaining the sustainable development priorities in the LRI are also illustrated with three examples of development-related processes. Urbanisation, dam construction, and aggregate mining occur within specific zones of the LRI (land, land–river, river, respectively), but their impacts can compromise sustainable development across the entire LRI and beyond. The existence of these unintended impacts highlights the need to consider the geomorphic, hydrological, and ecological processes within the LRI and how they interact with human activity. Identifying the place-based priorities and challenges for sustainable development will help achieve the SDGs without compromising the functions and services of the LRI.
... Water demands for irrigation, industries, households, and livestock were estimated at the grid cell resolution [25]. The water abstractions and allocation of demands are calculated using a dynamic allocation scheme [26]. Total water demands were met from three resources, namely from surface water, groundwater, or desalinated water (figure S1(c)). ...
Current global-scale models of water resources do not generally represent groundwater lateral flows and groundwater–surface water interactions. But, models that do represent groundwater in more detail are becoming available and this raises the question of how estimates of water flow, availability, and impacts might change compared to previous global estimates. In this study, we provide the first global quantification of cell-to-cell groundwater flow (GWF) using a high-resolution global-scale GWF model and compare estimated impacts of groundwater pumping using two model setups: (a) with and (b) without including cell-to-cell GWFs and realistic simulation of groundwater–surface water interactions at the global scale (simulated over 1960–2010). Results show that 40% of the land–surface cell-to-cell flows are a notable part of the cell’s water budget and that globally large differences in the impact of groundwater pumping are estimatd between the two runs. Globally, simulated groundwater discharge to rivers and streams increased by a factor of 1.2–2.2 when GWFs and interactions between groundwater and surface water were included. For eight heavily pumped aquifers, estimates of groundwater depletion decrease by a factor of 1.7–22. Furthermore, our results show that GWFs and interactions between groundwater and surface water contribute to the volume of groundwater that can be pumped without causing notable changes in storage. However, in approximately 40% of the world’s watersheds where groundwater is used, groundwater is being pumped notably at the expense of river flow, and in 15% of the area globally depletion is increased as a result of nearby groundwater pumping. Evaluation of the model results showed that when groundwater lateral flows and groundwater–-surface water interactions were taken into account, the indirect observations of groundwater depletion and groundwater discharge were mimicked much better than when these fluxes were not included. Based on these findings, we suggest that including GWFs in large-scale water resources assessments will benefit a realistic assessment of groundwater availability worldwide, the estimation of impacts associated with groundwater pumping, especially when one is interested in the feedback between groundwater use and groundwater and surface water availability, and the impacts of current and future groundwater uses on the hydrological system.
... The trades did not account for any changes in irrigation return flows which may lead to unintended third-party damages. This impact assessment, as pointed out by Qureshi et al. (2010) andde Graaf et al. (2014), depends on understanding specific irrigation efficiencies, soil types, identification of specific field, and other factors that will ultimately need to be considered in order to facilitate trading. Future work could address these dimensions, as well as formulating a more complex economic model that accounts for price discovery to allow the buyer to represent an agricultural interest. ...
Balancing out-of-stream water demands and ecological instream flows is a difficult challenge in watershed-scale management. Many watersheds already experience acute and chronic water shortages during average runoff years and may face more frequent and severe droughts in some locations due to climate and demographic change. Water markets may mitigate the economic consequences of shortages, but their potential is limited by the prevalence of all-or-nothing irrigate-or-fallow crop water use strategies. Irrigation water generally provides diminishing returns for crop productivity, so it may be possible to reduce water application at the margin with only a small loss in crop production, creating water savings that could be leased for other uses. We explore this scenario by combining a crop growth and hydrology (CropSyst) model with an economic model of farm profits and water trading, and apply it to the Walla Walla Basin in Washington State. Our results suggest that partial leasing of water rights through a deficit-irrigation strategy could economically benefit annual crop growers while meaningfully increasing water availability for stream flow augmentation.
... Water is an essential material in our daily life. Worldwide water demand increased substantially over the past decades as results of urbanization, agricultural intensification, population growth, and climate change and the accelerated development of modern industrial techniques [1][2][3]. To meet the demand for water resources in areas where reserves are insufficient, several countries have resorted to seawater desalination. ...
Energy consumption is a purely thermodynamic concept very useful in several scientific fields such as desalination, oceanography, biology, geochemistry and environmental processes, as well as in industrial applications. In this investigation, based on a thermodynamic approach, the calculation of energy consumption was evaluated during the desalination of seawater simulated to the aqueous ternary system {NaCl + KCl}( aq ). The mixing ionic parameters, obtained in our previous work, are used to predict the osmotic and activity coefficients in the aqueous solutions at different salinities ranging from 3.6 up to 72 g.L ⁻¹ at T = 298.15 K using the ion interaction model. The theoretical energy consumption of desalination was calculated at various salinities and recovery ratios.
... Of this fraction, nearly 2.5% is locked up in polar ice caps, glaciers and the atmosphere, leaving about 0.5% of water accessible to human needs in the form of river water and groundwater (Gude, 2017). Substantial increase in water withdrawals has led to severe water scarcity in many regions of the world (de Graaf et al., 2014;Greve et al., 2018;N Hanasaki et al., 2013). Likewise, climate change and drought intensities caused by the change in precipitation patterns and rising temperature are the contributing factors for depletion of available fresh water sources (Wanders and Wada, 2015). ...
While water is a key resource required to sustain life, freshwater sources and aquifers are being depleted at an alarming rate. As a mitigation strategy, saline water desalination is commonly used to supplement the available water resources beyond direct water supply. This is achieved through effective advanced water purification processes enabled to handle complex matrix of saline wastewater. Membrane technology has been extensively evaluated for water desalination. This includes the use of reverse osmosis (RO) (the most mature membrane technology for desalination), pervaporation (PV), electrodialysis (ED), membrane distillation (MD), and membrane crystallization (MCr). Though nanofiltration (NF) is not mainly applied for desalination purposes, it is included in the reviewed processes because of its ability to reach 90% salt rejection efficiency for water softening. However, its comparison with other technologies is not provided since NF cannot be used for removal of NaCl during desalination. Remarkably, membrane processes remain critically affected by several challenges including membrane fouling. Moreover, capital expenditure (CAPEX) and operating expenditure (OPEX) are the key factors influencing the establishment of water desalination processes. Therefore, this paper provides a concise and yet comprehensive review of the membrane processes used to desalt saline water. Furthermore, the successes and failures of each process are critically reviewed. Finally, the CAPEX and OPEX of these water desalination processes are reviewed and compared. Based on the findings of this review, MD is relatively comparable to RO in terms of process performance achieving 99% salt rejections. Also, high salt rejections are reported on ED and PV. The operation and maintenance (O&M) costs remain lower in ED. Notably, the small-scale MD OPEX falls below that of RO. However, the large-scale O&M in MD is rarely reported due to its slow industrial growth, thus making RO the most preferred in the current water desalination markets.
... GW is the water below the land surface, which can participate in the water cycle and can be renewed. The combination of SW and GW is called the Total Water Resources (TWR) (de Graaf et al., 2014). According to Moiwo, Tao, and Lu (Moiwo et al., 2013), TWR are closely related to the precipitation and its spatial/temporal distribution patterns in North China region. ...
After operating the middle route of South-to-North Water Diversion Project (SNWDP), the total water transfer to Beijing has exceeded 5.0 km³, bringing significant changes to the water use structure of Beijing. This article compiles historic data from 2007 to 2020 to analyze changes in water circulation, groundwater level, climate factors and subsidence patterns in Beijing following implementation of the middle SNWDP. It is found that the main current pressure on Beijing's water supply has come from improved living standards, the gradual popularization of water-using appliances, and a rapid development of the accommodation and catering industries. An InSAR time series approach was used to map subsidence in Beijing between 2007 and 2020 using satellite images from Sentinel-1A/B, Radarsat-2 and ALOS-1. Climate factors including precipitation and evapotranspiration were estimated using the Penman-Monteith-Leuning Evapotranspiration V2 (PML_V2) product. By compiling ground subsidence data for Beijing and corresponding climate data, the impact of the SNWDP and climate factors on groundwater levels and ground subsidence in Beijing were examined We identified three periods to characterize the changes of surface displacement after implementation of the SNWDP as a) the pre-effect stage, b) the effective stage, and c) the post-effective stage. The contribution of the SNWDP was apparent at the second stage, alleviating the problem of land subsidence to some extent. The ease of subsidence at different stages are accounted for 4%, 26.5%, and 41.7%, respectively, in terms of the mean velocity changes. Based on the result of some general circulation models. precipitation in the Beijing region is expected to increase over the next decade, implying a greater likelihood of rapid groundwater recovery. However, although groundwater is expected to recover in the long run, climate extremes in the future could possibly challenge the success of SNWDP during certain dry periods.
... Similar results can be found in other studies [14,42]. Meanwhile, irrigation may also increase the soil water contents and form runoff by return flows, in which the irrigation return flow to the groundwater is large in intensively irrigated basins and return flows cause a redistribution of unconsumed water over the water resources [43,44]. As a result, irrigation may alleviate hydrological drought at a short time scale [13]. ...
Understanding the propagation from meteorological to hydrological drought is crucial for hydrological drought monitoring and forecasting. In this study, daily precipitation and streamflow data of 16 sub-catchments in the Huaihe River Basin from 1980 to 2014 are used to establish a framework to quantitatively reveal the propagation relationship between meteorological and hydrological drought and explore the impact of climate, catchment properties, and human activities on drought propagation. The propagation from meteorological to hydrological drought is divided into three types. Type-1 propagation indicates that one or several meteorological droughts trigger a hydrological drought. The occurrence probability of Type-1 calculated by the conditional probability on SPI and SRI series varies from 0.25 to 0.48 among all catchments. Features of Type-1 propagation can be concluded as lengthening of duration, amplification of severity, lag of onset time, and reduction of speed. Type-2 propagation indicates that a meteorological drought occurs but no hydrological drought occurs, which accounts for 63–77% of the total meteorological drought events in all catchments. Type-3 indicates that a hydrological drought occurs without a proceeding meteorological drought, which is caused mostly by human activities. The occurrence probability of Type-3 ranges from 0.31 to 0.58. Climate factors have significant effects on hydrological drought duration, while catchment properties represented by topographic index and base flow index significantly relate to hydrological drought severity, propagation time, and occurrence probability of Type-1 propagation. The ratio of crop land reflecting irrigation on hydrological drought is far less than that of topographic index, denoting that the impact of irrigation on hydrological drought is less than that of catchment properties. Reservoirs have significant effects on alleviating the duration and severity of extreme hydrological droughts, but little effects on the average duration and severity of hydrological droughts.
... In this context, hydrological modelling becomes one of the powerful tools to develop required scenarios for sustainable management of water resources (Singh and Frevert, 2006;Beven, 2012;Beven and Young, 2013). Therefore, a wide range of hydrological models are developed and used for broad range of environmental processes and spatiotemporal scales (Beven and Kirkby, 1979;Refsgaard and Storm, 1990;Irannejad and Henderson-Sellers, 2007;Tang et al., 2006;Zhang et al., 2008Zhang et al., , 2016aZhang et al., , 2016bZhang et al., , 2020Zhang and Chiew, 2009;Schoener, 2010;de Graaf et al., 2014;Bai et al., 2020;Paul et al., 2020;Nagdeve et al., 2021). ...
Development and use of global, continental, and country scale hydrological models has attracted an increasing attention over the last two decades. Though developed countries are a head in development and assessment of these models, most developing countries, if not all, even do not have their own models. Therefore, an appropriate model selection process is necessary for these regions to improve the skill in hydrological modelling and prediction at the local-to-global scales. Therefore, a framework for model selection is provided to help hydrological modelers from various skills. Keeping the framework in view, this paper reviews 70 representative models to provide a lucid pathway of selecting models at global, continental and country scales over catchment scale models. In the process, strengths and weaknesses of models designed for each spatial extension are examined depending on their spatio-temporal resolutions, the model parameterization schemes for representing multiple hydrological processes, and the number of parameters. We summarize testing schemes to assess models to decide among multiple similar models. Finally, we summarize the remaining challenges and discuss future research directions.
... European Union policy is also aimed at protecting this resource, with the implementation of the Water Framework Directive (2000/60/EC) and the Urban Waste Water Treatment Directive (91/271/EEC). Factors such as the population growth in many urban areas, agricultural productivity, the economic development of different countries, industrialization, energy production, improvements in health and sanitation systems, and the expansion of irrigation systems in arid regions, have underscored the fact that conventional resources alone cannot meet the constantly growing demand [8][9][10][11][12][13][14]. ...
Given the problem of water scarcity and the importance of this resource for the sustainability of the planet, wastewater treatment and its costs have become a key issue for proper water management. Using bibliometric analysis of publications in the Web of Science database, this study presents an overview of the research on wastewater treatment costs in the period 1950–2020. The worldwide search returned 22,788 articles for wastewater treatment costs, which compares poorly to the results for research on wastewater treatment, accounting for only 12.34% of the total output on wastewater treatment. The findings of this study reveal the leading countries in this field of research (China, USA, India, Spain and the UK), with the articles being published in a wide range of high impact journals. Similarly, there are very few results on UV and chlorination costs, despite the importance of these two treatments for wastewater disinfection and reuse. This study is aimed at researchers in this field, helping them to identify recent trends, and at the main institutions in the scientific community working on this subject.
... Vörösmarty et al., 2000) and is shifting from agriculture to urbanization, which decreases irrigation return flows (e.g., Dinatale et al., 2008) and leads to a reduction in aquifer recharge (e.g. De Graaf et al., 2014). Water supplies are further impacted by climate change, which is increasing the number of in-stream sections that are dry for long periods in the year (Downing et al., 2012;Luce and Holden, 2009;Meehl et al., 2007;Steward et al., 2012). ...
Study region
This study is along an intermittent reach of the Alamosa River in the San Luis Valley of south-central Colorado, a river that is typical of the semi-arid southwestern United States with respect to climate, land use, and the impacts of upstream dam regulation.
Study focus
We use conceptual steady-state models to identify geologic factors that may control water loss through infiltration. These conceptual models are parameterized according to a range of conditions observed from stream discharge, topographic data, geologic data, and drone magnetometer data.
New hydrological insights
The introduction of a fault, variation in the alluvial aquifer hydraulic conductivity, and presence or absence of a confining unit in the numerical models were the primary geologic controls that affected infiltration across the study reach. Conversely, variation in the thickness of the streambed had little impact. This information may help determine future data collection within this and similar semi-arid regions where rivers are controlled by a combination of surface water availability (e.g. through dam regulation) and complex subsurface geology, which are often not well constrained.
... Country-level wastewater production, collection, treatment and reuse data were downscaled to 5 arcmin resolution (∼ 10 km at the Equator) based on the sum of averaged annual domestic and industrial return flow data (henceforth "return flow"). Return flows represent the water extracted for a specific sectoral purpose, but which is not consumed, and hence it returns to and dynamically interacts with surface and groundwater hydrology (de Graaf et al., 2014;Sutanudjaja et al., 2018). Return flows used for downscaling are calculated as gross − net water demands from the Water Futures and Solutions (WFaS) initiative for the years 2000-2010 . ...
Continually improving and affordable wastewater management provides opportunities for both
pollution reduction and clean water supply augmentation, while simultaneously promoting
sustainable development and supporting the transition to a circular economy. This study aims to
provide the first comprehensive and consistent global outlook on the state of domestic and
manufacturing wastewater production, collection, treatment and reuse. We use a data-driven approach,
collating, cross-examining and standardising country-level wastewater data from online data
resources. Where unavailable, data are estimated using multiple linear regression. Country-level
wastewater data are subsequently downscaled and validated at 5 arcmin
(∼10 km) resolution. This study estimates global wastewater production at 359.4×109 m3 yr−1, of which 63 % (225.6×109 m3 yr−1) is
collected and 52 % (188.1×109 m3 yr−1) is treated. By extension, we
estimate that 48 % of global wastewater production is released to the environment untreated,
which is substantially lower than previous estimates of ∼80 %. An estimated 40.7×109 m3 yr−1 of treated wastewater is intentionally reused. Substantial
differences in per capita wastewater production, collection and treatment are observed across
different geographic regions and by level of economic development. For example, just over 16 %
of the global population in high-income countries produces 41 % of global wastewater. Treated-wastewater reuse is particularly substantial in the Middle East and North Africa (15 %) and
western Europe (16 %), while comprising just 5.8 % and 5.7 % of the global population,
respectively. Our database serves as a reference for understanding the global wastewater status
and for identifying hotspots where untreated wastewater is released to the environment, which are
found particularly in South and Southeast Asia. Importantly, our results also serve as a baseline
for evaluating progress towards many policy goals that are both directly and indirectly connected
to wastewater management. Our spatially explicit results available at 5 arcmin
resolution are well suited for supporting more detailed hydrological analyses such as water
quality modelling and large-scale water resource assessments and can be accessed at
https://doi.org/10.1594/PANGAEA.918731 (Jones
et al., 2020).
... Increasing population and water demands for industrial, agricultural, and household uses, combined with climate change, is leading to an imbalance of water supply and demand in many regions, and challenging water resource management (e.g. Burri et al., 2019;de Graaf et al., 2014;Gleeson et al., 2012;Minnig et al., 2018). Especially in urban areas with industrial zones, the supply of drinking water from groundwater sources is further complicated due to potential groundwater contamination (Bertrand et al., 2016;Navarro and Carbonell, 2007). ...
Urban groundwater management requires a thorough and robust scientific understanding of flow and transport processes. ³H/³He apparent ages have been shown to efficiently help provide important groundwater-related information. However, this type of analysis is expensive as well as labor- and time-intensive, and hence limits the number of potential sampling locations.
To overcome this limitation, we established an inter-relationship between ³H/³He apparent groundwater ages and ⁴He concentrations analyzed in the field with a newly developed portable gas equilibrium membrane inlet mass spectrometer (GE-MIMS) system, and demonstrated that the results of the simpler GE-MIMS system are an accurate and reliable alternative to sophisticated laboratory based analyses. The combined use of ³H/³He lab-based ages and predicted ages from the ³H/³He–⁴He age relationship opens new opportunities for site characterization, and reveals insights into the conceptual understanding of groundwater systems.
For our study site, we combined groundwater ages with hydrochemical data, water isotopes (¹⁸O and ²H), and perchloroethylene (PCE) concentrations (1) to identify spatial inter-aquifer mixing between artificially infiltrated groundwater and water originating from regional flow paths and (2) to explain the spatial differences in PCE contamination within the observed groundwater system. Overall, low PCE concentrations and young ages occur when the fraction of artificially infiltrated water is high. The results obtained from the age distribution analysis are strongly supported by the information gained from the isotopic and hydrochemical data. Moreover, for some wells, fault-induced aquifer connectivity is identified as a preferential flow path for the transport of older groundwater, leading to elevated PCE concentrations.
... With social progress and economic development, demand for water is growing. The contradiction between supply and demand of water resources is becoming increasingly prominent [1]. A scientific and robust management of water resources is of great importance for the alleviation of water resource shortages, the sustainable utilization of water resources, and the maximization of regional ecological and economic benefits. ...
This paper addresses recent developments in the application of water Resource dispatching systems (WRDSs) in China. Through a survey of watershed managers and a literature analysis, it was found that water diversion projects should be the top priority of water resource management by considering the recovery construction of water diversion projects. Case studies of WRDSs in the South-to-North Water Diversion (SNWD) and Pearl River Basin are discussed in this article. The results show that total water consumption management (WCM), water quality monitoring and management (WQMM), minimum discharge flow management (MDFM), and water dispatch management (WDM) modules should be considered in WRDSs. Finally, strategies and needs for resolving water resource management problems are discussed, along with other applications of WRDSs in China.
... Y. Wada,van Beek, & Bierkens, 2011),(Yoshihide Wada et al., 2011), and(van Beek, Wada, & Bierkens, 2011). The index is similar to the geospatial Index of Local Relative Water Use by(Vorosmarty, Douglas, Green, & Revenga, 2005) in that it compares the summed domestic, industrial and agricultural water use (in volume per time unit) to the locally generated discharge including discharge from upstream cells. ...
... As a result, there remains a paucity of evidence quantifying ecosystem responses to empirically derived groundwater abstraction pressures ( Gleeson and Richter, 2018 ). Such ecological evidence and appraisals are urgently required given the pervasive effects of groundwater abstraction on riverine ecosystems, which have reduced river discharges by an average of 10% worldwide ( de Graaf et al., 2014 ), and greater societal water demands are projected to increase groundwater abstraction pressures in the future ( van Loon et al. 2016 ). ...
River flow regimes have been transformed by groundwater and surface water management operations globally, prompting widespread ecological responses. Yet, empirical evidence quantifying the simultaneous effects of groundwater and surface water management operations on freshwater ecosystems remains limited. This study combines a multi-decadal freshwater invertebrate dataset (1995-2016) with groundwater model outputs simulating the effects of different anthropogenic flow alterations (e.g. groundwater abstraction, effluent water returns) and river discharges. A suite of flow alteration and flow-ecology relationships were modelled that tested different invertebrate community responses (taxonomic, functional, flow response guilds, individual taxa). Most flow alteration-ecology
relationships were not statistically significant, highlighting the absence of consistent, detectable ecological responses to long-term water management operations. A small number of significant
statistical models provided insights into how flow alterations transformed specific ecological assets, including Ephemeroptera, Plecoptera and Trichoptera taxa which are rheophilic in nature being
positively associated with groundwater abstraction effects reducing river discharges by 0-15%. This represents a key finding from a water resource management operation perspective given that such flow
alteration conditions were observed on average in over two-thirds of the study sites examined. In a small number of instances, select invertebrate responses displayed relative declines associated with the most severe groundwater abstraction effects and artificial hydrological inputs (predominantly effluent water returns). The strongest flow-ecology relationships were recorded during spring months, when invertebrate communities were most responsive to antecedent minimum and maximum discharges, and average flow conditions in the preceding summer months. Results from this study provide novel evidence indicating how groundwater and surface water resources can be managed to conserve riverine ecological assets. Moreover, the ensemble of flow alteration- and flow-ecology relationships established in this study could be used to guide environmental flow strategies. Such findings are of global importance given that future climatic change and rising societal water demands are likely to further transform river flow regimes and threaten freshwater ecosystems.
... Studies have shown that 97.5% of the total water of the earth is seawater or brackish water, and only 0.4% of the rest is accessible for use because most of it is stored in the form of ice or under the earth [8][9][10]. About 700 million people are facing the water shortage crisis and the demand for fresh water is estimated to grow by 50% by 2025 [11,12]. It is therefore necessary to employ strategies that would mitigate water shortage. ...
The world is suffering from chronic water shortage due to the increasing population, water pollution, and industrialization. Desalinating saline water offers a rational choice to produce freshwater thus resolving the crisis. Among various kinds of desalination technologies, capacitive deionization (CDI) is of significant potential owing to the facile process, low energy consumption, mild working conditions, easy regeneration, low cost and the absence of secondary pollution. The electrode material is an essential component for desalination performance. The most used electrode material is carbon-based material, which suffers from low desalination capacity (under 15 mg·g −1). However, the desalination of saline water with the CDI method is usually the charging process of a battery or supercapacitor. The electrochemical capacity of battery electrode material is relatively high because of the larger scale of charge transfer due to the redox reaction, thus leading to a larger desalination capacity in the CDI system. A variety of battery materials have been developed due to the urgent demand for energy storage, which increases the choices of CDI electrode materials largely. Sodium-ion battery materials, lithium-ion battery materials, chloride-ion battery materials, conducting polymers, radical polymers, and flow battery electrode materials have appeared in the literature of CDI research, many of which enhanced the deionization performances of CDI, revealing a bright future of integrating battery materials with CDI technology.
... In the early 21st century, Döll and Siebert (2000) published the first digital global irrigation map at 0.5°spatial resolution by synthesizing and digitizing information obtained from governments, archived drawings, and international agencies. With booming computational power and the global irrigation map, global hydrology models (GHMs) and land surface models (LSMs) have been developed and improved to estimate the global water use in irrigation and other sectors (de Graaf et al., 2014;Döll & Siebert, 2002;Haddeland et al., 2006;Hanasaki et al., 2006Hanasaki et al., , 2018Leng et al., 2014;Nazemi & Wheater, 2015;Pokhrel et al., 2015;Rost et al., 2008;Sutanudjaja et al., 2018;Wada et al., 2010Wada et al., , 2013Wisser et al., 2008). Estimations of irrigation withdrawals from modeling-based approaches have a smaller range compared to that of accounting-based approaches, with the global irrigation water withdrawal estimated as 2,000 to 3,000 km 3 /year around year 2000 (Zhou et al., 2016). ...
Abstract Irrigation supports agricultural production, but widespread use of irrigation can perturb the regional and global water cycle. The one‐way coupled irrigation scheme used in some land surface models and Earth system models assumes that surface water demand is always met and ignores the surface water constraints, leading to overestimation of surface water usage, underestimation of groundwater pumping, and unrealistic simulation of their seasonal variability. To better represent the irrigation processes, a two‐way coupled irrigation scheme is developed within the Energy Exascale Earth System Model (E3SM). The new irrigation scheme simulates irrigation water demand and applies irrigation water in E3SM Land Model (ELM), which is coupled to a river routing model and a water management model (MOSART‐WM) that simulate streamflow, reservoir operations, and irrigation water supply. With two‐way coupling, surface water irrigation is constrained by the available runoff, streamflow, and reservoir storage. Simulations were performed for 1979–2008 at 0.5° spatial resolution to estimate irrigation surface water and groundwater use and their seasonality in global and large river basin scales. Compared to one‐way coupling, the two‐way coupling scheme (1) estimates less surface water withdrawal and less return flow due to the surface water constraint; (2) better represents groundwater recharge and groundwater level decline at global scale; and (3) is able to capture the seasonal dynamics of irrigation water allocations which reflect the local water conditions. The new development is an important step to more realistically account for the interactions between human water use and the terrestrial water cycle in an Earth system model.
... Country-level wastewater production, collection, treatment and re-use data was downscaled to 5 arc-minute resolution (~10km 210 at the equator) based on averaged sum of annual domestic and industrial return flow data (henceforth 'return flow') from the PCRaster GLOBal Water Balance Model for the years 2006 -2015 (PCR-GLOBWB 2; (Sutanudjaja et al., 2018)). Return flows represent the water extracted for a specific sectoral purpose, but is not consumed, and hence returns to and dynamically interacts with surface and ground water hydrology (de Graaf et al., 2014;Sutanudjaja et al., 2018). Domestic return flows only occurs where the urban and rural population have access to water, whereas industrial return flow occurs from all areas where 215 water is withdrawn . ...
Continually improving and affordable wastewater management provides opportunities for both pollution reduction and clean water supply augmentation, whilst simultaneously promoting sustainable development and supporting the transition to a circular economy. This study aims to provide the first comprehensive and consistent global outlook on the state of domestic and industrial wastewater production, collection, treatment and re-use. We use a data-driven approach, collating, cross-examining and standardising country-level wastewater data from online data resources. Where unavailable, data is estimated using multiple linear regression. Country-level wastewater data are subsequently downscaled and validated at 5 arc-minute (~ 10 km) resolution. This study estimates global wastewater production at 359.5 billion m3 yr−1, of which 63 % (225.6 billion m3 yr−1) is collected and 52 % (188.1 billion m3 yr−1) is treated. By extension, we estimate that 48 % of global wastewater production is released to the environment untreated, which is significantly lower than previous estimates of ~ 80 %. An estimated 40.7 billion m3 yr−1 of treated wastewater is intentionally re-used. Substantial differences in per capita wastewater production, collection and treatment are observed across different geographic regions and by level of economic development. For example, just over 16 % of the global population in high income countries produce 41 % of global wastewater. Treated wastewater re-use is particularly significant in the Middle East and North Africa (15 %) and Western Europe (16 %), while containing just 5.8 % and 5.7 % of the global population, respectively. Our database serves as a reference for understanding the global wastewater status and for identifying hotspots where untreated wastewater is released to the environment, which are found particularly in South and Southeast Asia. Importantly, our results also serve as a baseline for evaluating progress towards many policy goals that are both directly and indirectly connected to wastewater management (e.g. SDGs). Our spatially-explicit results available at 5 arc-minute resolution are well suited for supporting more detailed hydrological analyses such as water quality modelling and large-scale water resource assessments, and can be accessed at: https://doi.pangaea.de/10.1594/PANGAEA.918731 (Jones et al., 2020). A temporary link to this dataset for the review process can be accessed at: https://www.pangaea.de/tok/6631ef8746b59999071fa2e692fbc492c97352aa.
... Water withdrawal is set as equal to the gross water demand (summed over all sectors) and the groundwater pumping capacity is based on data from the IGRAC GGIS database. A prospective reservoir operation scheme is used in the model, which is dynamically calculated by evaluating the downstream water demand (de Graaf et al. 2014). More detailed information on PCR-GLOBWB v2.0 can be found in Wada et al. (2014) and Sutanudjaja et al. (2018). ...
As an extremely important region for the socioeconomic development of China, the Yangtze River Basin (YRB) is vulnerable to climate change and natural disasters. In recent decades, hydrological droughts have jeopardized regional water supply, local ecosystem services, and economic development in this region. This study simulates the characteristics of hydrological droughts in the YRB using the PCR-GLOBWB v2.0 model and the variable threshold method. High-spatial-resolution (about 10 km) PCR-GLOBWB v2.0 simulations considering the effects of human activities closely match the observed hydrological data for the YRB. Thus, the results indicate that human activities directly influence the tempo-spatial characteristics of hydrological droughts in the YRB. Reservoir operation decreases the multi-year monthly discharge but increases low flow in the severe drought years in the middle and lower subbasins of the YRB. These findings highlight the uneven effects of human activities on hydrological droughts in the YRB. In conclusion, anthropogenic activities must be considered when developing future mitigation and adaptation strategies for the YRB.
... Reservoirs are located on the drainage or river network based on the years of their construction from Global Reservoir and Dams Dataset (GRanD, Lehner et al., 2011). PCR-GLOBWB v2.0 uses a prospective reservoir operation scheme, which is dynamically calculated by evaluation of the downstream water demand (de Graaf et al., 2014) and is extended over multiple cells. The reservoir storage is subdivided by area to ensure that reservoir and lake levels are the same across their extent (Sutanudjaja et al., 2018). ...
How human activities have altered hydrological droughts (streamflow deficits) in China during the past five decades (1961–2016) is investigated using the latest version (v2.0) of PCR-GLOBWB model at high spatial resolution (~10 km). Although both human activities and climate variability have significant effects on river flows over China, there are large regional north-south contrasts. Over northern China, human activities generally intensify hydrological droughts. We find that human activities exacerbated drought deficit by about 70–200% from 2004 to 2015. In contrast, droughts over southern China are generally alleviated by human activities. For instance, irrigation and water management (such as reservoir operation and water abstraction) increase drought StDef (standardized drought deficit volume) by about 80% in the Yellow River (north) but reduce it by about 20% in the Yangtze River (south). Human activities slightly reduce drought deficit in the Yangtze River due to the combination of large reservoir storage and low ratio of agriculture consumption to abstracted irrigation water. In contrast, hydrological drought is aggravated in the semiarid Yellow River basin because of high water consumption from agricultural sectors. This study suggests that human activities have contrasting influences on hydrological drought characteristics in the northern (intensification) and southern (mitigation) parts of China. Therefore, it is critical to consider the variable roles of human activities on hydrological drought in China when developing mitigation and adaptation strategies.
... In many regions, groundwater is the sole source of accessible freshwater. In the rest of the world it is one of the most important sources for public and industrial water supply and agricultural irrigation de Graaf et al., 2014; and it is expected to become even more important under climate change Green, 2016). In Germany groundwater is of particular interest, as 73 % of the public water supply is taken from groundwater (Hölting and Coldewey, 2013). ...
Groundwater is the largest storage of freshwater worldwide and in Central Europe. It is the main source of public water supply and of crucial for agricultural irrigation, river discharge and surface water quality. As detailed observations of groundwater are scarce, analyses and predictions related to this topic are usually subject to large uncertainties. Particularly in the context of altered hydrological fluxes due to climate change it is important to broaden the scientific knowledge of the groundwater system and its sensitivity to climate. In consideration of numerous drought events in Central Europe during the last years, the groundwater’s reaction to drought and its role for the propagation of drought is of particular interest. This thesis comprises five studies which extend the understanding of Central European groundwater systems under drought and assess potential future changes based on the groundwater’s sensitivity to climate.
Droughts propagate through the hydrological cycle. Therefore, analyses on (groundwater) drought usually assess precipitation deficits as a first step to identify the relevant events. Due to the large number of available meteorological data sets, this step is not unambiguous. Study 1 of this thesis compares different data sets demonstrating the differences and commonalities resulting from different data set resolutions and interpolation algorithms. Altogether it can be concluded, that the absolute precipitation of low-resolution data sets is not an accurate measure for drought studies on a small scale whereas relative measures such as standardized indices are more reliable. These results serve as a basis for the methodology of the following studies.
The water quality of surface water depends on a variety of factors. Study 2 investigates the relationship between the deterioration of water quality during dry periods and catchment characteristics. It is shown that different properties are responsible for the responses of different water quality parameters. For example, there is a strong linkage between the geology in the catchment – which determines the chemical load of the groundwater – and the changes of sulfate concentration in the surface water during low flow. On the opposite, changes in the concentrations of chloride and nitrate during dry periods are mainly driven by the amount of sewage discharge within the catchment.
Every groundwater system reacts on different time scales to precipitation deficits corresponding to its local hydrogeological characteristics. Study 3 analyses the characteristic groundwater-baseflow response times to precipitation for a set of natural catchments across Germany. Based on that, potential future changes in the annual minimum flow are estimated using common features of climate projections for Central Europe. In most parts of Germany – especially in the Central German Uplands with its fractured rocks aquifers – response times are rather short, indicating a high sensitivity to decreasing summer precipitation. Hence, decreases in annual minimum flow are likely for the future in these catchments. On the contrary, porous aquifers often have much longer response times, therefore increases in winter precipitation could offset the decreased summer precipitation and no substantial changes in annual low flow are expected for these aquifers.
Groundwater systems are complex and highly heterogeneous over short distances. As long-term and near-natural observations are scarce, groundwater models are often inevitably the tools for research on groundwater-related processes. In study 4 a transient MODFLOW groundwater model is set up for Germany on a resolution of 1 km² and extensively evaluated. The model is able to depict the heterogeneous behaviour of groundwater head fluctuations due to different hydrogeological conditions. The aquifers differ in their sensitivity to short and long-term meteorological droughts and heterogeneous patterns of groundwater drought severity emerge for different drought events. The characteristic groundwater response time to precipitation is a good proxy to characterize different groundwater reaction types. It ranges in Germany from few months to several years and is strongly linked to hydrogeological and topographic parameters.
Changes in climate are expected to alter the hydrological cycle including drought. In study 5 the groundwaters’ and baseflows’ sensitivity to changes in recharge is assessed using model scenarios. Drier antecedent conditions due to longer drought events could lead to more severe groundwater drought events. On the opposite, a seasonal shift of recharge towards more winter and less summer recharge is not likely to exacerbate groundwater droughts much due to the delayed groundwater response. As baseflow reacts on shorter time scales it is more prone to severer short-term droughts. The groundwater and baseflow sensitivity to future climate changes is in general strongly linked to the local hydrogeological conditions.
In conclusion, this thesis demonstrates that the groundwaters’ reaction to drought is in Germany very heterogeneous. Characteristic responses to precipitation as well as trends of changes are hardly scalable due to the locally varying hydrogeological conditions. For detailed projections on water availability and water quality during drought – both under current and future climate conditions – multiple factors must be considered. Therefore, groundwater models are inevitable for extensive analyses and recent progress of groundwater representation in large-scale models offers new opportunities for enhanced predictions. Additionally, the groundwater response time to precipitation allows for an assessment of the groundwaters’ sensitivity to drought and potential future impacts. This thesis contributes to a profound understanding of the delayed and smoothed groundwater response to drought in Central Europe facilitating a more effective future water management.
... work of deGraaf et al. (2014),Wada et al. (2014),Sutanudjaja et al. (2018) andHanasaki et al. (2018). Water demand can be fulfilled by surface water and groundwater. ...
We develop a new large-scale hydrological and water resources model, the Community Water Model (CWatM), which can simulate hydrology both globally and regionally at different resolutions from 30 arc min to 30 arc sec at daily time steps. CWatM is open-source in the Python programming environment and has a modular structure. It uses global, freely available data in the netCDF4 file format for reading, storage, and production of data in a compact way. CWatM includes general surface and groundwater hydrological processes, but also takes into account human activities, such as water use and reservoir regulation, by calculating water demands, water use, and return flows. Reservoirs and lakes are included in the model scheme. CWatM is used in the framework of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP), which compares global model outputs. The flexible model structure allows dynamic interaction with hydro-economic and water quality models for the assessment and evaluation of water management options. Furthermore, the novelty of CWatM is its combination of state-of the-art hydrological modeling, modular programming, an online user manual and automatic source code documentation, global and regional assessments at different spatial resolutions, and a potential community to add to, change, and expand the open-source project. CWatM also strives to build a community learning environment which is able to freely use an open-source hydrological model and flexible coupling possibilities to other sectoral models, such as energy and agriculture.
... Groundwater resources, which are widely distributed and generally considered to be clean and unpolluted (Arto et al. 2016), comprise an important source of water. Groundwater is precious, especially in places where surface water resources are scarce (Graaf et al. 2014). However, anthropogenic activities have led to increases in natural groundwater pollution. ...
An in situ horizontal well (IHW) fan-shaped test tank was constructed in the laboratory. And nitrate removal rates were analyzed under different hydraulic loads. When the initial concentration of groundwater nitrate-N was 25 mg/L and the hydraulic load increased from 0.78 to 3.90 m³/(m² day), the results show that the nitrate-N concentration was less than 1.25 mg/L after the denitrification process stabilized. Additionally, the nitrate-N removal rate was over 95%. The concentration of nitrite-N was still below 1 mg/L, and the level of ammonia-N was between 0.5 and 1.00 mg/L. No increase in nitrite-N and ammonia-N concentration occurred during the test. The hydraulic conductivity of the medium in the horizontal well showed little variation, ranging from 34.09 to 31.64 m/day, indicating that there was no blockage caused by microbial growth in the IHW during the test. In addition, no ethanol was detected in the test tank except for the horizontal well, revealing that ethanol did not diffuse into the surrounding aquifer. Therefore, when the concentration of groundwater nitrate contamination is 25 mg/L, the hydraulic load under the IHW test tank condition is 3.90 m³/(m² day). The IHW test tank had a stable and good biological denitrification effect, and it can provide certain reference significance for in situ remediation of nitrate-contaminated groundwater.
... The worldwide demand for fresh and usable water has increased over the past decades due to population growth, economic development as well as expanded irrigation schemes, etc., [1,2]. Around 2 billion people are expected to suffer from water scarcity, of which, 95% (1.9 billion) may live in developing countries [3]. ...
The current global issue of water scarcity has demanded for over-abstraction of conventional freshwater resources. The states of water scarcity are anticipated to worsen, as by 2050 the population is estimated to reach 9 billion worldwide. Desalination is considered a solution to solve the water scarcity issues, as it is considered a drought-proof water source, which does not depend on climate change, river flows or reservoir levels. Moreover, membrane fouling is still the main "Achilles heel" for the effective operation of desalination systems. This makes the technology chemically, energetically and operationally intensive and requires a considerable infusion of capital. The application of an artificial neural network (ANN), the computing model inspired by the human brain, and its variants, have been developed that can optimize the operation of membrane-based desalination system through analyzing the complex experimental and real-time data. This review paper presents the recent trends and developments focussed primarily on the modelling and simulation of reverse osmosis (RO) plant using ANN to solve the challenging problem in membrane-based desalination systems. The literature review suggested that ANN has a potential application in predicting linear, nonlinear, complicated complex systems with high accuracy and with better control, prediction of membrane fouling, cost analysis. Therefore, ANN considered a strong basis to attract and motivate the researchers to work in this field in the future.
... The 2006 Human Development Report [43] estimates that average water use varies between 200-300 L per person per day in most European states, but is less than 10 L per person per day in developing countries. Population growth and the increase in per capita income leads to greater domestic water use and limits the supply available for other uses, such as agricultural irrigation; this situation is driving changes in wastewater management towards a greater level of reuse [44][45][46]. In light of the above, the following hypothesis can be posited: ...
Water scarcity in Mediterranean countries, especially in drought periods, justifies the use of wastewater. The deficit of water resources influences crop productivity and threatens environmental sustainability. The objective of this paper is to analyse whether agricultural production and irrigation area determine the volume of reused wastewater in Spain. To that end, a panel data model is estimated with 187 observations from 17 Spanish regions between 2004 and 2014. The results obtained show that wastewater reuse depends on agricultural variables as well as factors which affect the supply and demand of water. These include the relative scarcity of water resources; the availability of surface water, groundwater and desalinated water; the population; and the revenues collected for sanitation and wastewater treatment. Prevailing economic conditions, however, are not a determining factor. Therefore, there is an urgent need to develop appropriate management systems that guarantee the financing of sanitation and water reclamation services in all the regions that have significant crop production and scarcity of water resources.
Balancing human communities' and ecosystems' need for freshwater is one of the major challenges of the 21st century as population growth and improved living conditions put increasing pressure on freshwater resources. While frameworks to assess the environmental impacts of freshwater consumption have been proposed at the regional scale, an operational method to evaluate the consequences of consumption on different compartments of the water system and account for their interdependence is missing at the global scale. Here, we develop depletion factors that simultaneously quantify the effects of water consumption on streamflow, groundwater storage, soil moisture, and evapotranspiration globally. We estimate freshwater availability and water consumption using the output of a global-scale surface water-groundwater model for the period 1960-2000. The resulting depletion factors are provided for 8,664 river basins, representing 93% of the landmass with significant water consumption, i.e., excluding Greenland, Antarctica, deserts, and permanently frozen areas. Our findings show that water consumption leads to the largest water loss in rivers, followed by aquifers and soil, while simultaneously increasing evapotranspiration. Depletion factors vary regionally with ranges of up to four orders of magnitude depending on the annual consumption level, the type of water used, aridity, and water transfers between compartments. Our depletion factors provide valuable insights into the intertwined effects of surface and groundwater consumption on several hydrological variables over a specified period. The developed depletion factors can be integrated into sustainability assessment tools to quantify the ecological impacts of water consumption and help guide sustainable water management strategies, while accounting for the performance limitations of the underlying model.
Sustainable water resources management should guarantee that also future generations can fulfil their needs and that also natural systems still receive enough water. As we face multiple uses and stakeholders such as agriculture and food production, space for settlements and water supply, tourism, and nature conservation we need integrated modeling approaches to assess the complex impact of human activities on the water cycle. Additional pressures on water resources result from population growth and climate change. Ethiopia is a source region of the Nile River and famous for its water resources potential. The available annual average water per person per year is estimated to be 1575 m3. The Lake Tana accounts for 50% of the national fresh water. It has a total catchment area of about 15,321 km2 and hosts more than three million people. The climate is characterized by a high seasonality of rainfall with a rainy season between June and September. However, the scientific understanding of the hydrologic response to intensive agriculture, the interconnection of groundwater and surface water, and future perspectives of the water availability under global change is limited. Therefore, the main aim is to improve our understanding of past, present, and future hydrologic conditions in the Lake Tana Basin. To this end, hydrological modeling using SWAT (Soil and Water Assessment Tools) and a coupled surface water and groundwater model (SWAT-MODFLOW) were applied. Results from the models revealed a high connectivity of groundwater and surface water systems. Agricultural crops influence the hydrologic components differently. Groundwater recharge was relatively high on agricultural land covered by cereal crops, whereas surface runoff was significantly enhanced on cultivated land covered by legume crops like peas.
Irrigation is the dominant section of human water use, exerting essential impacts on hydrological processes and water resources. To more realistically simulate irrigation processes in water‐rich regions, an irrigation scheme is incorporated into a land surface‐hydrological model. It calculates the irrigation water requirement according to meteorological conditions, cropping area and growing stage, and root‐zone soil moisture, and determines the irrigation water withdrawal based on the available water resources as well as describing water extraction and irrigation processes in the model. The coupled model is applied to the Yangtze River Basin (YRB) in China, and verified using the observed daily river discharge from 1987 to 1990, evapotranspiration and irrigation amounts from 1999 to 2003. The results first show that the model can well reproduce hydrological processes within the basin, and the simulated irrigation largely agrees with the observation, in terms of annual irrigation and its spatial pattern. Second, inclusion of irrigation processes allows the model to better estimate evapotranspiration, with relative biases decreased from about −10% to −3%. It is also found that in comparison to arid/semi‐arid areas, although presenting a less effect on river discharge and groundwater, the irrigation in the YRB significantly alters hydrological processes through water redistribution. The irrigation‐induced evapotranspiration increment and runoff decrease indicate a shift in the surface water and energy balance, implying a potential effect on the atmosphere. Therefore, representing irrigation processes properly is important, particularly for understanding the coupling effect of the nature‐human system and improving the hydrological prediction accuracy.
Reduced river discharge and flow regulation are significant threats to freshwater biodiversity. An accurate representation of potential damage of water consumption on freshwater biodiversity is required to quantify and compare the environmental impacts of global value chains. The effect of discharge reduction on fish species richness was previously modeled in life cycle impact assessment, but models were limited by the restricted geographical scope of underlying species-discharge relationships and the small number of species data. Here, we propose a model based on a novel regionalized species-discharge relationship (SDR). Our SDR-based model covers 88 % of the global landmass (2320 river basins worldwide excluding deserts and permanently frozen areas) and is based on a global dataset of 11,450 riverine fish species, simulated river discharge, elevation, and climate zones. We performed 10-fold cross-validation to select the best set of predictors and validated the obtained SDRs based on observed discharge data. Our model performed better than previous SDRs employed in life cycle impact assessment (Kling-Gupta efficiency coefficient about 4 times larger). We provide both marginal and average models with their uncertainty ranges for assessing scenarios of small and large-scale water consumption, respectively, and include regional and global species loss. We conducted an illustrative case study to showcase the method's applicability and highlight the differences with the currently used approach. Our models are useful for supporting sustainable water consumption and riverine fish biodiversity conservation decisions. They enable a more specific, reliable, and complete impact assessment by differentiating impacts on regional riverine fish species richness and irreversible global losses, including up-to-date species data, and providing spatially explicit values with high geographical coverage.
The branched and looped type networks are the two basic configurations of water distribution. The branched pipe networks are generally designed by traditional and optimization methods. In the traditional method, a pipeline is designed by balancing the available energy against the loss of energy due to friction, whereas in the optimization methods, the cost is minimized. For ensuring regular water supply, it is essential to consider the reliability of the water distribution network, which depends on the failure rate of pipes, quality and quantity of water available at the source, and pressure requirements at demand nodes. Therefore, the reliability of the system needs to be incorporated while minimizing the total cost of the distribution system. In this paper, an enumerative method using both the reliability and total annual cost is developed for designing the branched pipe networks. The method satisfies pressure and discharges requirements along with the recommended values of the minimum and maximum velocities in the pipes. In this method, different sets of pipe sizes are taken to calculate the reliability and cost of the network, and that set of the pipe network is selected, which has the highest ratio of reliability to cost. To calculate the ratio of reliability to cost, the capital cost or the total annual cost can be used. The total annual cost is the sum of the annual fixed and annual energy costs. The applicability of the developed method is illustrated with the help of a design example. It was found that the reliability of the branched network varied with the total annual cost, as well as the capital cost, of the network for different sets of pipe diameters in the network. Further, it was found that the reliability for the designed network using total annual cost was higher than using capital cost. Therefore, the total annual cost should be preferred over the capital cost in the design to establish the balance between reliability and economy. The presented method provides a straightforward approach for water supply engineers to determine economical as well as reliable branched pipe networks.KeywordsPipe networkCapital costTotal annual costReliabilityReliability cost ratio
India being mainly an agricultural country, its economic, domestic consumption, industrial as well as financial sector depends on agriculture, which is adversely affected by soil erosion. Soil erosion within watersheds causes an increase in reservoir sedimentation, reducing their storage capacity and life span as well. Knowing the severity of erosion in an area contributes to effective soil conservation practices. Therefore, this study employs remote sensing, GIS and software to compute average annual soil loss in IWMP-45 Bhokarpada, Dist Raigad of Maharashtra by using the RUSLE equation. QGIS enables the extraction of spatial maps including DEM, rainfall erosivity, land slope, land use and land cover, data and values of the five RUSLE factors. Data for the study area has been obtained from Bhuvan, IMD (Indian Meteorological Department) and ISRO (Indian Space Research Organization). The results of this study area showed that the soil erosion was 163 ton/year in the study area which is severe and will require protection and conservation plans immediately. The soil erosion quantity mainly varies because of topography and land use-land cover. The study shows that under high and very high erosion region is about 21%.KeywordsRUSLEErosivity factorTopographic factorSoil erodibility factor
This paper reports on the application of a daily rainfall-runoff model HYSIM upstream of Kangsabati reservoir, covering three drought-prone districts of West Bengal. The upstream part comprises mainly of two rivers upper Kangsabati river and Kumari river and they have their outlets at the Kangsabati reservoir. A lumped conceptual hydrological model linked to a Geographical Information System was developed on the basis of simplified physical process representations (infiltration, evapotranspiration, base flow, interflow, overland flow, channel routing), using conventional hydro-meteorological data and readily accessible geographical maps. The model parameters were estimated from a Digital Elevation Model, soil and landuse maps, and only four parameters were calibrated for the sub basins. The results of both calibration and validation were compared on the basis of their performance with regards to objective criteria representing the Index of agreement, the Nash and Sutcliffe efficiency and the correlation coefficient. Analysis showed that monthly objective criteria values for both the sub basin were mostly more than daily as rainfall compiled for a longer period is more precise than for a shorter period of time. For the Kangsabati sub basin, the flow was well simulated by the model, following the trend of observed flows. However, the peaks of simulated flows were more than the observed flow due to the effect of storage structures in the upstream of gauging stations. However, simulated peaks well matched the peak in rainfall. Furthermore, for the Kumari sub basin, the Nash–Sutcliffe Efficiency was very less, i.e. 0.05 in the validation period and 0.32 during the calibration period as the observed mean flow was very less during the validation period due to the more amounts of abstractions. The findings imply that nonavailability of abstractions data as well as the storage capacity of structures built by local people, in the upstream part of gauging stations, poses great challenges to modeling of discharge in a river.KeywordsCalibrationHYSIMKangsabati reservoirStorage structureSub basinValidation
Continental- to global-scale hydrologic and land surface models increasingly include representations of the groundwater system. Such large-scale models are essential for examining, communicating, and understanding the dynamic interactions between the Earth system above and below the land surface as well as the opportunities and limits of groundwater resources. We argue that both large-scale and regional-scale groundwater models have utility, strengths, and limitations, so continued modeling at both scales is essential and mutually beneficial. A crucial quest is how to evaluate the realism, capabilities, and performance of large-scale groundwater models given their modeling purpose of addressing large-scale science or sustainability questions as well as limitations in data availability and commensurability. Evaluation should identify if, when, or where large-scale models achieve their purpose or where opportunities for improvements exist so that such models better achieve their purpose. We suggest that reproducing the spatiotemporal details of regional-scale models and matching local data are not relevant goals. Instead, it is important to decide on reasonable model expectations regarding when a large-scale model is performing “well enough”
in the context of its specific purpose. The decision of reasonable
expectations is necessarily subjective even if the evaluation criteria are
quantitative. Our objective is to provide recommendations for improving the
evaluation of groundwater representation in continental- to global-scale
models. We describe current modeling strategies and evaluation practices,
and we subsequently discuss the value of three evaluation strategies: (1) comparing model outputs with available observations of groundwater levels or
other state or flux variables (observation-based evaluation), (2) comparing
several models with each other with or without reference to actual
observations (model-based evaluation), and (3) comparing model behavior with
expert expectations of hydrologic behaviors in particular regions or at
particular times (expert-based evaluation). Based on evolving practices in
model evaluation as well as innovations in observations, machine learning,
and expert elicitation, we argue that combining observation-, model-, and
expert-based model evaluation approaches, while accounting for
commensurability issues, may significantly improve the realism of
groundwater representation in large-scale models, thus advancing our ability
for quantification, understanding, and prediction of crucial Earth science
and sustainability problems. We encourage greater community-level
communication and cooperation on this quest, including among global
hydrology and land surface modelers, local to regional hydrogeologists, and
hydrologists focused on model development and evaluation.
Increasing population, economic growth and changes in diet have dramatically
increased the demand for food and water over the last decades. To meet
increasing demands, irrigated agriculture has expanded into semi-arid areas
with limited precipitation and surface water availability. This has greatly
intensified the dependence of irrigated crops on groundwater withdrawal and
caused a steady increase in groundwater withdrawal and groundwater depletion. One of the effects of groundwater pumping is the reduction in
streamflow through capture of groundwater recharge, with detrimental effects
on aquatic ecosystems. The degree to which groundwater withdrawal affects
streamflow or groundwater storage depends on the nature of the
groundwater–surface water interaction (GWSI). So far, analytical solutions that have been derived to calculate the impact of groundwater on streamflow
depletion involve single wells and streams and do not allow the GWSI to
shift from connected to disconnected, i.e. from a situation with two-way interaction to one with a one-way interaction between groundwater and surface water. Including this shift and also analysing the effects of many wells requires numerical groundwater models that are expensive to set up.
Here, we introduce an analytical framework based on a simple lumped
conceptual model that allows us to estimate to what extent groundwater withdrawal affects groundwater heads and streamflow at regional scales. It
accounts for a shift in GWSI, calculates at which critical withdrawal rate
such a shift is expected, and when it is likely to occur after withdrawal commences. It also provides estimates of streamflow depletion and which part
of the groundwater withdrawal comes out of groundwater storage and which
parts from a reduction in streamflow. After a local sensitivity analysis,
the framework is combined with parameters and inputs from a global
hydrological model and subsequently used to provide global maps of critical
withdrawal rates and timing, the areas where current withdrawal exceeds
critical limits and maps of groundwater and streamflow depletion rates that result from groundwater withdrawal. The resulting global
depletion rates are compared with estimates from in situ observations and regional and global groundwater models and satellites. Pairing of the
analytical framework with more complex global hydrological models presents a
screening tool for fast first-order assessments of regional-scale
groundwater sustainability and for supporting hydro-economic models that require simple relationships between groundwater withdrawal rates and the evolution of pumping costs and environmental externalities.
Water resource management (WRM) practices, such as groundwater and surface water abstractions and effluent discharges, may impact baseflow. Here the CAMELS-GB large-sample hydrology dataset is used to assess the impacts of such practices on Baseflow Index (BFI) using statistical models of 429 catchments from Great Britain. Two complementary modelling schemes, multiple linear regression (LR) and machine learning (random forests, RF), are used to investigate the relationship between BFI and two sets of covariates (natural covariates only and a combined set of natural and WRM covariates). The LR and RF models show good agreement between explanatory covariates. In all models, the extent of fractured aquifers, clay soils, non-aquifers, and crop cover in catchments, catchment topography, and aridity are significant or important natural covariates in explaining BFI. When WRM terms are included, groundwater abstraction is significant or the most important WRM covariate in both modelling schemes, and effluent discharge to rivers is also identified as significant or influential, although natural covariates still provide the main explanatory power of the models. Surface water abstraction is a significant covariate in the LR model but of only minor importance in the RF model. Reservoir storage
covariates are not significant or are unimportant in both the LR and RF
models for this large-sample analysis. Inclusion of WRM terms improves the
performance of some models in specific catchments. The LR models of high BFI catchments with relatively high levels of groundwater abstraction show the greatest improvements, and there is some evidence of improvement in LR
models of catchments with moderate to high effluent discharges. However,
there is no evidence that the inclusion of the WRM covariates improves the
performance of LR models for catchments with high surface water abstraction
or that they improve the performance of the RF models. These observations
are discussed within a conceptual framework for baseflow generation that
incorporates WRM practices. A wide range of schemes and measures are used to manage water resources in the UK. These include conjunctive-use and low-flow alleviation schemes and hands-off flow measures. Systematic information on such schemes is currently unavailable in CAMELS-GB, and their specific effects on BFI cannot be constrained by the current study. Given the significance or importance of WRM terms in the models, it is recommended that information on WRM, particularly groundwater abstraction, should be included where possible in future large-sample hydrological datasets and in the analysis and prediction of BFI and other measures of baseflow.
Study region
The catchment above Bengbu in the Huaihe River Basin, China
Study focus
In the Anthropocene, hydrological drought is significantly affected by human activities, and the degree of different human activities affecting droughts may vary in different physiographic and anthropogenic contexts. This study aims to quantify the relative contributions of various human activities on hydrological droughts using “scenario comparison” method based on a calibrated PCR-GLOBWB model.
New hydrological insights for the region
The impacts on hydrological droughts by human activities exhibit large differences over time and space. In terms of time, non-irrigation water use (NWU) and irrigation water use (IWU) increased standardized drought streamflow deficit (SDSD) by about 119 % and 214 % on average during 1981–2010, respectively. In terms of space, NWU heavily increased SDSD in most regions of the basin, whereas reduced it in the regions with limited surface water due to the return flow from unconsumed water to surface water. IWU reduced SDSD in paddy irrigation regions due to large quantities of water in the upstream rivers were transferred to those regions for flooding irrigation, whereas in non-paddy irrigation regions IWU increased SDSD due to most of water being withdrawn locally and comparatively small quantity of water transfer. Reservoir operation (RO) reduced SDSD in downstream water receiving areas while increased SDSD in upstream areas. Our findings can help drought management and mitigation.
Freshwater salinisation is a growing problem, yet cross-regional assessments of freshwater salinity status and the impact of agricultural and other sectoral uses are lacking. Here, we assess inland freshwater salinity patterns and evaluate its interactions with irrigation water use, across seven regional river basins (401 river sub-basins) around the world, using long-term (1980–2010) salinity observations. While a limited number of sub-basins show persistent salinity problems, many sub-basins temporarily exceeded safe irrigation water-use thresholds and 57% experience increasing salinisation trends. We further investigate the role of agricultural activities as drivers of salinisation and find common contributions of irrigation-specific activities (irrigation water withdrawals, return flows and irrigated area) in sub-basins of high salinity levels and increasing salinisation trends, compared to regions without salinity issues. Our results stress the need for considering these irrigation-specific drivers when developing management strategies and as a key human component in water quality modelling and assessment. Freshwater salinisation is a growing water quality problem, but impacts and drivers across regional to global scales have been lacking. A new assessment of inter-regional freshwater salinisation demonstrates the importance of irrigation as a driver of salinisation.
Water resource management (WRM) practices, such as abstractions and discharges, may impact baseflow. Here the CAMELS-GB large-sample hydrology dataset is used to assess the impacts of such practices on baseflow index (BFI) using statistical models of 429 catchments from Great Britain. Two complementary modelling schemes, multiple linear regression (LR) and machine learning (random forests, RF), are used to investigate the relationship between BFI and two sets of covariates (natural covariates only and a combined set of natural and WRM covariates). The LR and RF models show good agreement between explanatory covariates. In all models, the extent of fractured aquifers, clay soils, non-aquifers, and crop cover in catchments, catchment topography and aridity are significant or important natural covariates in explaining BFI. When WRM terms are included, groundwater abstraction is significant or the most important WRM covariate in both modelling schemes and discharge to rivers is also identified as significant or influential, although natural covariates still provide the main explanatory power of the models. Surface water abstraction is a significant covariate in the LR model but of only minor importance in the RF model. Reservoir storage covariates are not significant or are unimportant in both the LR and RF models for this large-sample analysis. Inclusion of WRM terms improves the performance of some models in specific catchments. The LR models of high BFI catchments with relatively high levels of groundwater abstraction show the greatest improvements, and there is some evidence of improvement in LR models of catchments with moderate to high discharges. However, there is no evidence that the inclusion of the WRM covariates improves the performance of LR models for catchments with high surface water abstraction or that they improve the performance of the RF models. These observations are used to formulate a conceptual framework for baseflow generation that incorporates WRM practices. It is recommended that information on WRM, particularly groundwater abstraction, should be included where possible in future large-sample hydrological data sets and in the analysis and prediction of BFI and other measures of baseflow.
In the humid, temperate Delaware River Basin (DRB) where water availability is generally reliable, summer low flows can cause competition between various human and ecological water uses. As temperatures continue to rise, population increases and development expands, it is critical to understand historical low flow variability to anticipate and plan for future flows. Using a sample of 325 U.S. Geological Survey gages, we evaluated spatial patterns in several low flow metrics, the biophysical and climatic drivers of these metrics, and trends in low flows for two periods: 1950-2018 and 1980-2018. We calculated the annual 7-day low flow and date, low flow deficit as the departure below a long-term daily flow threshold and the number of discrete low flow periods below this threshold. We also aggregated several climate metrics to watershed scale and used existing watershed properties quantifying land cover, topography, soils, geology, and human activity. Random forest models were used to assess the hierarchy of variable importance in explaining mean-annual low flow variability for each low flow metric using all gages. We find muted regional patterns in mean-annual low flow and low flow variability, likely due to the myriad of anthropogenic, landscape, and flow modifications that obscure flow regimes from their natural characteristics. In contrast, individual years show markedly different spatial patterns in low flow magnitude and severity. Coincident with increases in precipitation, 7-day low flows have generally increased and low flow deficits decreased for both 1950-2018 and 1980-2018 periods. However, 7-day low flows have decreased in the Coastal Plain physiographic province where water use and impervious area have increased in recent decades, highlighting the effects of land and water management on low flows. With continued change expected in the DRB, additional research needs are highlighted to enable estimation of future low flows and to plan for periods of prolonged low flow.
Baseflow has become an important source of nitrate nonpoint source pollution in many intensive agricultural watersheds. Uncertainties in baseflow nutrient load separation are caused by the effects of hydrometeorological factors on both baseflow recession and baseflow nutrient load recession. These uncertainties have not been addressed well in the existing separating algorithms, which are based on simple baseflow rate–load relationships. In the present study, a recursive tracing source algorithm (RTSA) was developed based on a nonlinear reservoir algorithm and hydrometeorology‐corrected baseflow nutrient load recession parameter. This approach was used to reduce the uncertainty of baseflow nitrate load estimation caused by variations in different load recessions under varying climate conditions. RTSA validation in a typical rainy agricultural watershed yielded Nash‐Sutcliffe efficiency (NSE), root mean square error‐observation standard deviation ratio (RSR), and R2 values of 0.91, 0.30, and 0.91, respectively. The baseflow nitrate–nitrogen (N‐NO3–) loads from 2003 to 2012 in the Changle River watershed of eastern China were estimated with the RTSA. The results indicated that baseflow nitrate export accounted for 62.0% of the mean total annual N‐NO3– loads (18.0 kg/ha). The total baseflow N‐NO3– export was highest in spring (3.6 kg/ha), followed by summer (3.2 kg/ha), winter (2.3 kg/ha), and autumn (2.1 kg/ha). The contribution of baseflow to total nitrate in the stream decreased in the order of winter (69.88%) > spring (66.59%) > autumn (60.36%) > summer (54.04%). The monthly baseflow N‐NO3– loads and flow‐weighted concentrations greatly increased during the research period (Mann‐Kendall test, Zs > 2.56, p < 0.01). Without proper countermeasures, baseflow nitrate may represent a serious long‐term risk for water surfaces in the future.
We develop a new large-scale hydrological and water resources model, the Community Water Model (CWatM), which can simulate hydrology both globally and regionally at different resolutions from 30 arcmin to 30 arcsec at daily time steps. CWatM is open source in the Python programming environment and has a modular structure. It uses global, freely available data in the netCDF4 file format for reading, storage, and production of data in a compact way. CWatM includes general surface and groundwater hydrological processes but also takes into account human activities, such as water use and reservoir regulation, by calculating water demands, water use, and return flows. Reservoirs and lakes are included in the model scheme. CWatM is used in the framework of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP), which compares global model outputs. The flexible model structure allows for dynamic interaction with hydro-economic and water quality models for the assessment and evaluation of water management options. Furthermore, the novelty of CWatM is its combination of state-of-the-art hydrological modeling, modular programming, an online user manual and automatic source code documentation, global and regional assessments at different spatial resolutions, and a potential community to add to, change, and expand the open-source project. CWatM also strives to build a community learning environment which is able to freely use an open-source hydrological model and flexible coupling possibilities to other sectoral models, such as energy and agriculture.
During the past decades, human water use has more than doubled, yet available freshwater resources are finite. As a result, water scarcity has been prevalent in various regions of the world. Here, we present the first global assessment of past development of water stress considering not only climate variability but also growing water demand, desalinated water use and non-renewable groundwater abstraction over the period 1960–2001 at a spatial resolution of 0.5°. Agricultural water demand is estimated based on past extents of irrigated areas and livestock densities. We approximate past economic development based on GDP, energy and household consumption and electricity production, which are subsequently used together with population numbers to estimate industrial and domestic water demand. Climate variability is expressed by simulated blue water availability defined by freshwater in rivers, lakes, wetlands and reservoirs by means of the global hydrological model PCR-GLOBWB. We thus define blue water stress by comparing blue water availability with corresponding net total blue water demand by means of the commonly used, Water Scarcity Index. The results show a drastic increase in the global population living under water-stressed conditions (i.e. moderate to high water stress) due to growing water demand, primarily for irrigation, which has more than doubled from 1708/818 to 3708/1832 km<sup>3</sup> yr<sup>−1</sup> (gross/net) over the period 1960–2000. We estimate that 800 million people or 27% of the global population were living under water-stressed conditions for 1960. This number is eventually increased to 2.6 billion or 43% for 2000. Our results indicate that increased water demand is a decisive factor for heightened water stress in various regions such as India and North China, enhancing the intensity of water stress up to 200%, while climate variability is often a main determinant of extreme events. However, our results also suggest that in several emerging and developing economies (e.g. India, Turkey, Romania and Cuba) some of past extreme events were anthropogenically driven due to increased water demand rather than being climate-induced.
In regions with frequent water stress and large aquifer systems groundwater is often used as an additional water source. If groundwater abstraction exceeds the natural groundwater recharge for extensive areas and long times, overexploitation or persistent groundwater depletion occurs. Here we provide a global overview of groundwater depletion (here defined as abstraction in excess of recharge) by assessing groundwater recharge with a global hydrological model and subtracting estimates of groundwater abstraction. Restricting our analysis to sub-humid to arid areas we estimate the total global groundwater depletion to have increased from 126 (±32) km3 a−1 in 1960 to 283 (±40) km3 a−1 in 2000. The latter equals 39 (±10)% of the global yearly groundwater abstraction, 2 (±0.6)% of the global yearly groundwater recharge, 0.8 (±0.1)% of the global yearly continental runoff and 0.4 (±0.06)% of the global yearly evaporation, contributing a considerable amount of 0.8 (±0.1) mm a−1 to current sea-level rise.
To sustain growing food demand and increasing standard of living, global
water withdrawal and consumptive water use have been increasing rapidly.
To analyze the human perturbation on water resources consistently over a
large scale, a number of macro-scale hydrological models (MHMs) have
been developed over the recent decades. However, few models consider the
feedback between water availability and water demand, and even fewer
models explicitly incorporate water allocation from surface water and
groundwater resources. Here, we integrate a global water demand model
into a global water balance model, and simulate water withdrawal and
consumptive water use over the period 1979-2010, considering water
allocation from surface water and groundwater resources and explicitly
taking into account feedbacks between supply and demand, using two
re-analysis products: ERA-Interim and MERRA. We implement an irrigation
water scheme, which works dynamically with daily surface and soil water
balance, and include a newly available extensive reservoir data set.
Simulated surface water and groundwater withdrawal show generally good
agreement with available reported national and sub-national statistics.
The results show a consistent increase in both surface water and
groundwater use worldwide, but groundwater use has been increasing more
rapidly than surface water use since the 1990s. Human impacts on
terrestrial water storage (TWS) signals are evident, altering the
seasonal and inter-annual variability. The alteration is particularly
large over the heavily regulated basins such as the Colorado and the
Columbia, and over the major irrigated basins such as the Mississippi,
the Indus, and the Ganges. Including human water use generally improves
the correlation of simulated TWS anomalies with those of the GRACE
observations.
Water used by irrigated crops is obtained from three sources: local precipitation contributing to soil moisture available for root water uptake (i.e., green water), irrigation water taken from rivers, lakes, reservoirs, wetlands, and renewable groundwater (i.e., blue water), and irrigation water abstracted from nonrenewable groundwater and nonlocal water resources. Here we quantify globally the amount of nonrenewable or nonsustainable groundwater abstraction to sustain current irrigation practice. We use the global hydrological model PCR-GLOBWB to simulate gross crop water demand for irrigated crops and available blue and green water to meet this demand. We downscale country statistics of groundwater abstraction by considering the part of net total water demand that cannot be met by surface freshwater. We subsequently confront these with simulated groundwater recharge, including return flow from irrigation to estimate nonrenewable groundwater abstraction. Results show that nonrenewable groundwater abstraction contributes approximately 20% to the global gross irrigation water demand for the year 2000. The contribution of nonrenewable groundwater abstraction to irrigation is largest in India (68 km 3 yr -1) followed by Pakistan (35 km 3 yr -1), the United States (30 km 3 yr -1), Iran (20 km 3 yr -1), China (20 km 3 yr -1), Mexico (10 km 3 yr -1), and Saudi Arabia (10 km 3 yr -1). Results also show that globally, this contribution more than tripled from 75 to 234 km 3 yr -1 over the period 1960-2000.
During the past decades, human water use more than doubled, yet available freshwater resources are finite. As a result, water scarcity has been prevalent in various regions of the world. Here, we present the first global assessment of past development of water scarcity considering not only climate variability but also growing water demand, desalinated water use and non-renewable groundwater abstraction over the period 1960-2001 at a spatial resolution of 0.5°. Agricultural water demand is estimated based on past extents of irrigated areas and livestock densities. We approximate past economic development based on GDP, energy and household consumption and electricity production, which is subsequently used together with population numbers to estimate industrial and domestic water demand. Climate variability is expressed by simulated blue water availability defined by freshwater in rivers, lakes and reservoirs by means of the global hydrological model PCR-GLOBWB. The results show a drastic increase in the global population living under water-stressed conditions (i.e., moderate to high water stress) due to the growing water demand, primarily for irrigation, which more than doubled from 1708/818 to 3708/1832 km3 yr-1 (gross/net) over the period 1960-2000. We estimate that 800 million people or 27 % of the global population were under water-stressed conditions for 1960. This number increased to 2.6 billion or 43 % for 2000. Our results indicate that increased water demand is the decisive factor for the heightened water stress, enhancing the intensity of water stress up to 200 %, while climate variability is often the main determinant of onsets for extreme events, i.e. major droughts. However, our results also suggest that in several emerging and developing economies (e.g., India, Turkey, Romania and Cuba) some of the past observed droughts were anthropogenically driven due to increased water demand rather than being climate-induced. In those countries, it can be seen that human water consumption is a major factor contributing to the high intensity of major drought events.
Surface fresh water (i.e., blue water) is a vital and indispensable resource for human water use in the agricultural, industrial, and domestic sectors. In this paper, global water availability is calculated by forcing the global hydrological model PCR-GLOBWB with daily global meteorological fields for the period 1958-2001. To represent blue water availability, a prognostic reservoir operation scheme was included in order to produce monthly time series of global river discharge modulated by reservoir operations. To specify green water availability for irrigated areas, actual transpiration from the model was used. Thus, the computed water availability reflects the climatic variability over 1958-2001 and is contrasted against the monthly water demand using the year 2000 as a benchmark in the companion paper. As the water that is withdrawn to meet demand directly interferes with blue water availability along the drainage network, this paper evaluates model performance for three regimes reflecting different degrees of human interference: natural discharge, discharge regulated by reservoirs, and modified discharge. In the case of modified discharge, the net blue water demand for the year 2000 is subtracted directly from the regulated discharge, taking water demand equal to consumptive water use. Results show that model simulations of monthly river discharge compare well with observations from most of the large rivers. Exceptions are basins subject to large extractions for irrigation purposes, where simulated discharge exceeds the observations even when water demand is taken into account. Including the prognostic reservoir operation scheme results in mixed performance, with a poorer approximation of peak flows but with a marginally better simulation of low flows and persistence. A comparison of simulated actual evapotranspiration with that from the ERA-40 reanalysis as a proxy for observed rates shows similar patterns over nonirrigated areas but substantial deviations over major irrigated areas. As expected, assimilated actual evapotranspiration over these areas includes water from alternative sources, whereas the simulations with PCR-GLOBWB are limited by soil moisture, i.e., green water availability. On the basis of this evidence we conclude that the simulation provides adequate fields of water availability to assess water stress at the monthly scale, for which a separate validation is provided in the companion paper.
The sensitivity to spatial scale of runoff produced by the variable infiltration capacity (VIC) macroscale hydrologic model is investigated by implementing the model over the Columbia and Arkansas-Red River basins at spatial resolutions from one-eighth to 2° latitude by longitude. At lower resolutions the meteorological, topographical, and land cover data at the highest spatial resolution are averaged spatially. Simulated mean annual streamflow at lower resolutions is as much as 18 and 12% lower for the Arkansas-Red and Columbia River basins, respectively, as compared to the one-eighth degree implementation. When the VIC model subgrid parameterization for spatial precipitation variability is implemented, the model's sensitivity to spatial scale decreases slightly in the Arkansas-Red River basin, where total runoff at lower resolutions decreases by up to 14% relative to the high-resolution runs. In the Columbia River basin, total runoff is only 4% lower at 2° resolution than at one-eighth degree resolution when precipitation variation with elevation is reparameterized at lower resolutions in a manner that replicates mean annual precipitation in the corresponding higher-resolution cells.
Agricultural water use accounts for around 70% of the total water that is withdrawn from surface water and groundwater. We use a new, gridded, global-scale water balance model to estimate interannual variability in global irrigation water demand arising from climate data sets and uncertainties arising from agricultural and climate data sets. We used contemporary maps of irrigation and crop distribution, and so do not account for variability or trends in irrigation area or cropping. We used two different global maps of irrigation and two different reconstructions of daily weather 1963–2002. Simulated global irrigation water demand varied by ∼30%, depending on irrigation map or weather data. The combined effect of irrigation map and weather data generated a global irrigation water use range of 2200 to 3800 km3 a−1. Weather driven variability in global irrigation was generally less than ±300 km3 a−1, globally (
This paper assesses global water stress at a finer temporal scale compared to conventional assessments. To calculate time series of global water stress at a monthly time scale, global water availability, as obtained from simulations of monthly river discharge from the companion paper, is confronted with global monthly water demand. Water demand is defined here as the volume of water required by users to satisfy their needs. Water demand is calculated for the benchmark year of 2000 and contrasted against blue water availability, reflecting climatic variability over the period 1958–2001. Despite the use of the single benchmark year with monthly variations in water demand, simulated water stress agrees well with long‐term records of observed water shortage in temperate, (sub)tropical, and (semi)arid countries, indicating that on shorter (i.e., decadal) time scales, climatic variability is often the main determinant of water stress. With the monthly resolution the number of people experiencing water scarcity increases by more than 40% compared to conventional annual assessments that do not account for seasonality and interannual variability. The results show that blue water stress is often intense and frequent in densely populated regions (e.g., India, United States, Spain, and northeastern China). By this method, regions vulnerable to infrequent but detrimental water stress could be equally identified (e.g., southeastern United Kingdom and northwestern Russia).
Groundwater is a life-sustaining resource that supplies water to billions of people, plays a central part in irrigated agriculture and influences the health of many ecosystems. Most assessments of global water resources have focused on surface water, but unsustainable depletion of groundwater has recently been documented on both regional and global scales. It remains unclear how the rate of global groundwater depletion compares to the rate of natural renewal and the supply needed to support ecosystems. Here we define the groundwater footprint (the area required to sustain groundwater use and groundwater-dependent ecosystem services) and show that humans are overexploiting groundwater in many large aquifers that are critical to agriculture, especially in Asia and North America. We estimate that the size of the global groundwater footprint is currently about 3.5 times the actual area of aquifers and that about 1.7 billion people live in areas where groundwater resources and/or groundwater-dependent ecosystems are under threat. That said, 80 per cent of aquifers have a groundwater footprint that is less than their area, meaning that the net global value is driven by a few heavily overexploited aquifers. The groundwater footprint is the first tool suitable for consistently evaluating the use, renewal and ecosystem requirements of groundwater at an aquifer scale. It can be combined with the water footprint and virtual water calculations, and be used to assess the potential for increasing agricultural yields with renewable groundwaterref. The method could be modified to evaluate other resources with renewal rates that are slow and spatially heterogeneous, such as fisheries, forestry or soil.
ERA-Interim is the latest global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The ERA-Interim project was conducted in part to prepare for a new atmospheric reanalysis to replace ERA-40, which will extend back to the early part of the twentieth century. This article describes the forecast model, data assimilation method, and input datasets used to produce ERA-Interim, and discusses the performance of the system. Special emphasis is placed on various difficulties encountered in the production of ERA-40, including the representation of the hydrological cycle, the quality of the stratospheric circulation, and the consistency in time of the reanalysed fields. We provide evidence for substantial improvements in each of these aspects. We also identify areas where further work is needed and describe opportunities and objectives for future reanalysis projects at ECMWF.
1] This study quantifies, spatially explicitly and in a consistent modeling framework (Lund-Potsdam-Jena managed Land), the global consumption of both ''blue'' water (withdrawn for irrigation from rivers, lakes and aquifers) and ''green'' water (precipitation) by rainfed and irrigated agriculture and by nonagricultural terrestrial ecosystems. In addition, the individual effects of human-induced land cover change and irrigation were quantified to assess the overall hydrological impact of global agriculture in the past century. The contributions to irrigation of nonrenewable (fossil groundwater) and nonlocal blue water (e.g., from diverted rivers) were derived from the difference between a simulation in which these resources were implicitly considered (IPOT) and a simulation in which they were neglected (ILIM). We found that global cropland consumed >7200 km 3 year À1 of green water in 1971–2000, representing 92% (ILIM) and 85% (IPOT), respectively, of total crop water consumption. Even on irrigated cropland, 35% (ILIM) and 20% (IPOT) of water consumption consisted of green water. An additional 8155 km 3 year À1 of green water was consumed on grazing land; a further $44,700 km 3 year À1 sustained the ecosystems. Blue water consumption predominated only in intensively irrigated regions and was estimated at 636 km 3 year À1 (ILIM) and 1364 km 3 year À1 (IPOT) globally, suggesting that presently almost half of the irrigation water stemmed from nonrenewable and nonlocal sources. Land cover conversion reduced global evapotranspiration by 2.8% and increased discharge by 5.0% (1764 km 3 year À1), whereas irrigation increased evapotranspiration by up to 1.9% and decreased discharge by 0.5% at least (IPOT, 1971–2000). The diverse water fluxes displayed considerable interannual and interdecadal variability due to climatic variations and the progressive increase of the global area under cultivation and irrigation.
We describe the construction of a 10′ latitude/longitude data set of mean monthly surface climate over global land areas, excluding Antarctica. The climatology includes 8 climate elements-precipitation, wet-day frequency, temperature, temperature, diurnal temperature range, relative humidity, sunshine duration, ground frost frequency and windspeed-and was interpolated from a data set of station means for the period centred on 1961 to 1990. Precipitation was first defined in terms of the parameters of the Gamma distribution, enabling the calculation of monthly precipitation at any given return period. The data are compared to an earlier data set at 0.5° latitude/longitude resolution and show added value over most regions. The data will have many applications in applied climatology, biogeochemical modelling, hydrology and agricultural meteorology and are available through the International Water Management Institute World Water and Climate Atlas (http://www.iwmi.org) and the Climatic Research Unit (http://www.cru.uea.ac.uk).
The future adequacy of freshwater resources is difficult to assess, owing to a complex and rapidly changing geography of water supply and use. Numerical experiments combining climate model outputs, water budgets, and socioeconomic information along digitized river networks demonstrate that (i) a large proportion of the world's population is currently experiencing water stress and (ii) rising water demands greatly outweigh greenhouse warming in defining the state of global water systems to 2025. Consideration of direct human impacts on global water supply remains a poorly articulated but potentially important facet of the larger global change question.
The authors describe the construction of a 0.5°lat-long gridded dataset
of monthly terrestrial surface climate for the period of 1901-96.
The dataset comprises a suite of seven climate elements: precipitation,
mean temperature, diurnal temperature range, wet-day frequency, vapor
pressure, cloud cover, and ground frost frequency. The spatial coverage
extends over all land areas, including oceanic islands but excluding
Antarctica. Fields of monthly climate anomalies, relative to the
1961-90 mean, were interpolated from surface climate data. The anomaly
grids were then combined with a 1961-90 mean monthly climatology
(described in Part I) to arrive at grids of monthly climate over
the 96-yr period. The primary variables-precipitation, mean temperature,
and diurnal temperature range-were interpolated directly from station
observations. The resulting time series are compared with other coarser-resolution
datasets of similar temporal extent. The remaining climatic elements,
termed secondary variables, were interpolated from merged datasets
comprising station observations and, in regions where there were
no station data, synthetic data estimated using predictive relationships
with the primary variables. These predictive relationships are described
and evaluated. It is argued that this new dataset represents an advance
over other products because (i) it has higher spatial resolution
than other datasets of similar temporal extent, (ii) it has longer
temporal coverage than other products of similar spatial resolution,
(iii) it encompasses a more extensive suite of surface climate variables
than available elsewhere, and (iv) the construction method ensures
that strict temporal fidelity is maintained. The dataset should be
of particular relevance to a number of applications in applied climatology,
including large-scale biogeochemical and hydrological modeling, climate
change scenario construction, evaluation of regional climate models,
and comparison with satellite products. The dataset is available
from the Climatic Research Unit and is currently being updated to
1998. The authors describe the construction of a 0.5° lat-long gridded
dataset of monthly terrestrial surface climate for the period of
1901-96. The dataset comprises a suite of seven climate elements:
precipitation, mean temperature, diurnal temperature range, wet-day
frequency, vapor pressure, cloud cover, and ground frost frequency.
The spatial coverage extends over all land areas, including oceanic
islands but excluding Antarctica. Fields of monthly climate anomalies,
relative to the 1961-90 mean, we interpolated from surface climate
data. The anomaly grids were then combined with a 1961-90 mean monthly
climatology (described in Part I) to arrive at grids of monthly climate
over the 96-yr period. The primary variables - precipitation, mean
temperature, and diurnal temperature range - were interpolated directly
from station observations. The resulting time series are compared
with other coarser-resolution datasets of similar temporal extent.
The remaining climatic elements, termed secondary variables, were
interpolated from merged datasets comprising station observations
and, in regions where there were no station data, synthetic data
estimated using predictive relationships with the primary variables.
These predictive relationships are described and evaluated. It is
argued that this new dataset represents an advance over other products
because (i) it has higher spatial resolution than other datasets
of similar temporal extent, (ii) it has longer temporal coverage
than other products of similar spatial resolution, (iii) it encompasses
a more extensive suite of surface climate variables than available
elsewhere, and (iv) the construction method ensures that strict temporal
fidelity is maintained. The dataset should be of particular relevance
to a number of applications in applied climatology, including large-scale
biogeochemical and hydrological modeling, climate change scenario
construction, evaluation of regional climate models, and comparison
with satellite products. The dataset is available from the Climatic
Research Unit and is currently being updated to 1998.
Aquifers are the primary source of drinking water for up to two billion people. To avoid overexploitation, lengthy renewal periods of some aquifers must be taken into account.
About 70% of global human water withdrawal from rivers, reservoirs, and aquifers is for irrigation of agricultural land, and about one third of global food production relies on irrigation water. Irrigation systems, however, are usually rather ineffective; much of the withdrawn water is lost before it reaches the plants that require the water for optimal growth. The efficiency of irrigation often is lower than half of the optimum (depending e.g. on climate and irrigation system), such that the accuracy of modelled efficiency may have strong effects on the simulated water cycle and the distribution, seasonal phenology, and productivity (yields) of crop types. Therefore, it is crucial to estimate irrigation efficiencies as detailed as possible in any (large-scale) irrigation assessment. In this study, generic irrigation functional types (IFTs) have been developed for a better representation of irrigation in the dynamic global vegetation and water balance model including managed land, LPJmL (Bondeau et al., 2006). LPJ is a model of intermediate complexity, representing the intra- and interannual dynamics of terrestrial vegetation (both natural and agricultural) and the associated biophysical and biogeochemical processes (e.g. carbon and water fluxes). Irrigation of agricultural vegetation is one important option of land and water management in this model. The IFTs developed here improve the way in which irrigation efficiencies have been considered in the pilot version of LPJmL. With the introduction of IFTs into LPJmL together with the recently implemented discharge accumulation along a global river topology (Jachner et al., submitted), water flows on agricultural land are represented in a more precise manner. The present country-scale IFT classification was derived from the dominant irrigation method (surface, sprinkler, or micro-irrigation), irrigation field size, and the associated management system, based on an extensive review of literature and data archives. We determine an overall irrigation project efficiency for each country. This overall efficiency is comprised by a combination of individual (partial) efficiencies that capture water losses a) from the conveyance systems (conveyance efficiency), b) when the irrigation water is brought to the field (field application efficiency), and c) a management factor determined by the irrigation system size, which is a substitute of distribution efficiency (the unequal distribution of irrigation water across the fields). The effectiveness in terms of timeliness of delivery is represented by application of scheduling rules. The dominant irrigation method is used to assign the respective IFT to each country; for a few countries where relevant data were not available, a statistical assignment procedure based on socio-economic and climatic information was employed. The resulting country-scale irrigation efficiencies are tabulated and presented in global maps. Our efficiencies compare well with earlier values that had been derived for larger regions; yet, the present study provides more detailed and consistent estimates of irrigation efficiencies, which owing to their generic nature are suited for application in any large-scale model that represents agricultural water use.
ERA-40 is a re-analysis of meteorological observations from September 1957 to August 2002 produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) in collaboration with many institutions. The observing system changed considerably over this re-analysis period, with assimilable data provided by a succession of satellite-borne instruments from the 1970s onwards, supplemented by increasing numbers of observations from aircraft, ocean-buoys and other surface platforms, but with a declining number of radiosonde ascents since the late 1980s. The observations used in ERA-40 were accumulated from many sources. The first part of this paper describes the data acquisition and the principal changes in data type and coverage over the period. It also describes the data assimilation system used for ERA-40. This benefited from many of the changes introduced into operational forecasting since the mid-1990s, when the systems used for the 15-year ECMWF re-analysis (ERA-15) and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis were implemented. Several of the improvements are discussed. General aspects of the production of the analyses are also summarized.
A new digital map of the lithology of the continental surfaces is proposed in vector mode (n ≈ 8300, reaggregated at 0.5° × 0.5° resolution) for 15 rock types (plus water and ice) targeted to surficial Earth system analysis (chemical weathering, land erosion, carbon cycling, sediment formation, riverine fluxes, aquifer typology, coastal erosion). These types include acid (0.98% at global scale) and basic (5.75%) volcanics, acid (7.23%) and basic (0.20%) plutonics, Precambrian basement (11.52%) and metamorphic rocks (4.07%), consolidated siliciclastic rocks (16.28%), mixed sedimentary (7.75%), carbonates (10.40%), semi- to un-consolidated sedimentary rocks (10.05%), alluvial deposits (15.48%), loess (2.62%), dunes (1.54%) and evaporites (0.12%). Where sediments, volcanics and metamorphosed rocks are too intimately mixed, a complex lithology (5.45%) class is added. Average composition is then tabulated for continents, ocean drainage basins, relief types (n = 7), 10° latitudinal bands, geological periods (n = 7), and exorheic versus endorheic domain and for formerly glaciated regions. Surficial lithology is highly heterogeneous and major differences are noted in any of these ensembles. Expected findings include the importance of alluvium and unconsolidated deposits in plains and lowlands, of Precambrian and metamorphic rocks in mid-mountain areas, the occurrence of loess, dunes and evaporites in dry regions, and of carbonates in Europe. Less expected are the large occurrences of volcanics (74% of their outcrops) in highly dissected relief and the importance of loess in South America. Prevalence of carbonate rocks between 15°N and 65°N and of Precambrian plus metamorphics in two bands (25°S–15°N and north of 55°N) is confirmed. Asia and the Atlantic Ocean drainage basin, without Mediterranean and Black Sea, are the most representative ensembles. In cratons the influence of ancient geological periods is often masked by young sediments, while active orogens have a specific composition.
Fresh water is a renewable resource, but it is also finite. Around the world, there are now numerous signs that human water use exceeds sustainable levels. Groundwater depletion, low or nonexistent river flows, and worsening pollution levels are among the more obvious indicators of water stress. In many areas, extracting more water for human uses jeopardizes the health of vital aquatic ecosystems. Satisfying the increased demands for food, water, and material goods of a growing global population while at the same time protecting the ecological services provided by natural water ecosystems requires new approaches to using and managing fresh water. In this article, I propose a global effort (1) to ensure that freshwater ecosystems receive the quantity, quality, and timing of flows needed for them to perform their ecological functions and (2) to work toward a goal of doubling water productivity. Meeting these challenges will require policies that promote rather than discourage water efficiency, as well as new partnerships that cross disciplinary and professional boundaries.
Anthropogenic activities have been significantly perturbing global freshwater flows and groundwater reserves. Despite numerous advances in the development of land surface models (LSMs) and global terrestrial hydrological models (GHMs), relatively few studies have attempted to simulate the impacts of anthropogenic activities on the terrestrial water cycle using the framework of LSMs. From the comparison of simulated terrestrial water storage with theGravity Recovery and Climate Experiment (GRACE) satellite observations it is found that a process-based LSM, the Minimal Advanced Treatments of Surface Interaction and Runoff (MATSIRO), outperforms the bucket-model-based GHM called H08 in simulating hydrologic variables, particularly in water-limited regions. Therefore, the water regulation modules of H08 are incorporated into MATSIRO. Further, a new irrigation scheme based on the soil moisture deficit is developed. Incorporation of anthropogenic water regulation modules significantly improves river discharge simulation in the heavily regulated global river basins. Simulated irrigation water withdrawal for the year 2000 (2462 km 3 yr -1) agreeswell with the estimates provided by the Food and Agriculture Organization (FAO). Results indicate that irrigation changes surface energy balance, causing a maximum increase of ̃50 W m -2 in latent heat flux averaged over June-August. Moreover, unsustainable anthropogenic water use in 2000 is estimated to be ̃450 km 3 yr -1, which corresponds well with documented records of groundwater overdraft, representing an encouraging improvement over the previousmodeling studies.Globally, unsustainablewater use accounts for̃40%of blue water used for irrigation. The representation of anthropogenic activities in MATSIRO makes the model a suitable tool for assessing potential anthropogenic impacts on global water resources and hydrology.
Humans have strongly impacted the global water cycle, not only water flows but also water storage. We have performed a first global-scale analysis of the impact of water withdrawals on water storage variations, using the global water resources and use model WaterGAP. This required estimation of fractions of total water withdrawals from groundwater, considering five water use sectors. According to our assessment, the source of 35% of the water withdrawn worldwide (4300 km3/year during 1998–2002) is groundwater. Groundwater contributes 42%, 36% and 27% of water used for irrigation, households and manufacturing, respectively, while we assume that only surface water is used for livestock and for cooling of thermal power plants. Consumptive water use was 1400 km3/year during 1998–2002. It is the sum of the net abstraction of 250 km3/year of groundwater (taking into account evapotranspiration and return flows of withdrawn surface water and groundwater) and the net abstraction of 1150 km3/year of surface water. Computed net abstractions indicate, for the first time at the global scale, where and when human water withdrawals decrease or increase groundwater or surface water storage. In regions with extensive surface water irrigation, such as Southern China, net abstractions from groundwater are negative, i.e. groundwater is recharged by irrigation. The opposite is true for areas dominated by groundwater irrigation, such as in the High Plains aquifer of the central USA, where net abstraction of surface water is negative because return flow of withdrawn groundwater recharges the surface water compartments. In intensively irrigated areas, the amplitude of seasonal total water storage variations is generally increased due to human water use; however, in some areas, it is decreased. For the High Plains aquifer and the whole Mississippi basin, modeled groundwater and total water storage variations were compared with estimates of groundwater storage variations based on groundwater table observations, and with estimates of total water storage variations from the GRACE satellites mission. Due to the difficulty in estimating area-averaged seasonal groundwater storage variations from point observations of groundwater levels, it is uncertain whether WaterGAP underestimates actual variations or not. We conclude that WaterGAP possibly overestimates water withdrawals in the High Plains aquifer where impact of human water use on water storage is readily discernible based on WaterGAP calculations and groundwater observations. No final conclusion can be drawn regarding the possibility of monitoring water withdrawals in the High Plains aquifer using GRACE. For the less intensively irrigated Mississippi basin, observed and modeled seasonal groundwater storage reveals a discernible impact of water withdrawals in the basin, but this is not the case for total water storage such that water withdrawals at the scale of the whole Mississippi basin cannot be monitored by GRACE.
A database of monthly climate observations from meteorological stations is constructed. The database includes six climate elements and extends over the global land surface. The database is checked for inhomogeneities in the station records using an automated method that refines previous methods by using incomplete and partially overlapping records and by detecting inhomogeneities with opposite signs in different seasons. The method includes the development of reference series using neighbouring stations. Information from different sources about a single station may be combined, even without an overlapping period, using a reference series. Thus, a longer station record may be obtained and fragmentation of records reduced. The reference series also enables 1961–90 normals to be calculated for a larger proportion of stations.
The station anomalies are interpolated onto a 0.5° grid covering the global land surface (excluding Antarctica) and combined with a published normal from 1961–90. Thus, climate grids are constructed for nine climate variables (temperature, diurnal temperature range, daily minimum and maximum temperatures, precipitation, wet-day frequency, frost-day frequency, vapour pressure, and cloud cover) for the period 1901–2002. This dataset is known as CRU TS 2.1 and is publicly available (http://www.cru.uea.ac.uk/). Copyright
Drawing upon a variety of existing maps, data and information, a new Global Lakes and Wetlands Database (GLWD) has been created. The combination of best available sources for lakes and wetlands on a global scale (1:1 to 1:3 million resolution), and the application of Geographic Information System (GIS) functionality enabled the generation of a database which focuses in three coordinated levels on (1) large lakes and reservoirs, (2) smaller water bodies, and (3) wetlands. Level 1 comprises the shoreline polygons of the 3067 largest lakes (surface area ≥50 km2) and 654 largest reservoirs (storage capacity ≥0.5 km3) worldwide, and offers extensive attribute data. Level 2 contains the shoreline polygons of approx. 250,000 smaller lakes, reservoirs and rivers (surface area ≥0.1 km2), excluding all water bodies of level 1. Finally, level 3 represents lakes, reservoirs, rivers, and different wetland types in the form of a global raster map at 30-second resolution, including all water bodies of levels 1 and 2.In a validation against documented data, GLWD proved to represent a comprehensive database of global lakes ≥1 km2 and to provide a good representation of the maximum global wetland extent. GLWD-1 and GLWD-2 establish two global polygon maps to which existing lake registers, compilations or remote sensing data can be linked in order to allow for further analyses in a GIS environment. GLWD-3 may serve as an estimate of wetland extents for global hydrology and climatology models, or to identify large-scale wetland distributions and important wetland complexes.