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Global Assessment of Water Stress in Karst Regions in a Changing World (GloW)

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Tunde Olarinoye
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Analysis of karst spring recession hydrographs is essential for determining hydraulic parameters, geometric characteristics and transfer mechanisms that describe the dynamic nature of karst aquifer systems. The extraction and separation of different fast and slow flow components constituting karst spring recession hydrograph typically involve manual and subjective procedures. This subjectivity introduces bias, while manual procedures can introduce errors to the derived parameters representing the system. To provide an alternative recession extraction procedure that is automated, fully objective and easy to apply, we modified traditional streamflow extraction methods to identify components relevant for karst spring recession analysis. Mangin’s karst-specific recession analysis model was fitted to individual extracted recession segments to determine matrix and conduit recession parameters. We introduced different parameters optimisation approaches of the Mangin’s model to increase degree of freedom thereby allowing for more parameters interaction. The modified recession extraction and parameters optimisation approaches were tested on 3 karst springs in different climate conditions. The results show that the modified extraction methods are capable of distinguishing different recession components and derived parameters reasonably represent the analysed karst systems. We recorded an average KGE >0.7 among all recession events simulated by recession parameters derived from all combinations of recession extraction methods and parameters optimisation approaches. While there are variability among parameters estimated by different combinations of extraction methods and optimisation approaches, we find even much higher variability among individual recession events. We provide suggestions to reduce the uncertainty among individual recession events and to create a more robust analysis by using multiple pairs of recession extraction method and parameters optimisation approach.
Andreas Hartmann
added a research item
Comprehensive management of karst water resources requires sufficient understanding of their dynamics and karst-specific modeling tools. However, the limited availability of observations of karstic groundwater dynamics has been prohibiting the assessment of karst water resources at regional to global scales. This paper presents the first global effort to integrate experimental approaches and large-scale modeling. Using a global soil-moisture monitoring program and a global database of karst spring discharges, the simulations of a preliminary global karstic-groundwater-recharge model are evaluated. It is shown that soil moisture is a crucial variable that better distinguishes recharge dynamics in different climates and for different land cover types. The newly developed dataset of karst spring discharges provides first insights into the wide variability of discharge volumes and recharge areas of different karst springs around the globe. Comparing the model simulations with the newly collected soil-moisture and spring-discharge observations, indicates that (1) improvements of the recharge model are still necessary to obtain a better representation of different land cover types and snow processes, and (2) there is a need to incorporate groundwater dynamics. Applying and strictly evaluating these improvements in the model will finally provide a tool to identify hot spots of current or future water scarcity in the karst regions around the globe, thus supporting national and international water governance.
Andreas Hartmann
added 6 research items
Karst systems are characterized by a high subsurface heterogeneity, and their complex recharge processes are difficult to characterize. Experimental methods to study karst systems mostly focus on analysing the entire aquifer. Despite their important role in recharge processes, the soil and epikarst receive limited attention, and the few available studies were performed at sites of similar latitudes. In this paper, we describe a new monitoring network that allows for the improvement of the understanding of soil and epikarst processes by including different karst systems with different land-cover types in different climate regions. Here, we present preliminary data form the network and elaborate on their potential to answer research questions about the role of soil and epikarst on karstic water flow and storage. The network measures soil moisture at multiple points and depths to understand the partitioning of rainfall into infiltration, evapotranspiration, and groundwater recharge processes. We installed soil moisture probes at five different climate regions: Puerto Rico (tropical), Spain (Mediterranean), the United Kingdom (humid oceanic), Germany (humid mountainous), and Australia (dry semi-arid). At each of the five sites, we defined two 20 m×20 m plots with different land-use types (forest and grassland). At each plot, 15 soil moisture profiles were randomly selected and probes at different depths from the topsoil to the epikarst (in total over 400 soil moisture probes) were installed. Covering the spatio-temporal variability of flow processes through a large number of profiles, our monitoring network will allow researchers to develop a new conceptual understanding of evapotranspiration and groundwater recharge processes in karst regions across different climate regions and land-use types, and this will provide the base for quantitative assessment with physically based modelling approaches in the future.
Hydrological research is often focused at the catchment scale; but there are significant benefits from taking a broader spatial perspective (i.e. comparative hydrology) to advance understanding of hydrological processes, especially in the context of global change. Indeed, many of the recently described ‘unsolved problems in hydrology’ (Blöschl et al., 2019) refer to either global-scale processes (e.g. climate change), the hydrology of major physiographic zones (e.g. semi-arid or snowmelt regions) or require extensive comparisons across catchments. Moving beyond the catchment-scale frequently provides more holistic insights into the varying spatio-temporal response of hydrological systems to climate variability and change, as well as to the myriad of other anthropogenic influences on water. This knowledge is key for both mitigation of, and adaption to, hazards under an increasingly changed water cycle (Abbot et al., 2019). Moreover, a large-scale viewpoint is essential to inform appropriate water management towards socio-economic development, water-food-energy security and ecosystem health (e.g. WWAP, 2019). Here we contest that taking a large-scale perspective can bring significant benefits to understanding hydrological processes under change. After making the case for a need for large-scale hydrology, we then explain the benefit of a large-scale hydrology approach for investigating global change, its causes, as well as water management in the present day and into the future. We conclude by identifying challenges and opportunities to advance research in large-scale hydrology and hydrological process understanding beyond the individual catchment.
The shallow subsurface of karst systems (soil and epikarst) plays an important role in karst recharge processes. However, only a little research that directly characterized this zone has been conducted. In this paper, we review previous studies that focus on the soil and epikarst recharge processes, in particular on diffuse recharge processes. The literature is categorized by processes, methods and controlling factors, summarized in an overview table, and discussed in detail. Finally, new directions to advance research toward a better understanding of the hydrological dynamics in the karstic shallow subsurface are derived.
Andreas Hartmann
added a research item
Substantial changes of climate and land use are projected in many karst regions in the world for the next decades. Despite these projections, only few studies have been performed to quantify the impact of climate change and land use change on karst water resources. This is mainly due to a lack of observations of the karstic recharge and groundwater dynamics, which is prohibiting the development large-scale karst simulation models. Here we present the advances of the first global effort to develop a simulation tool to support (inter)national governance of karst water resources. Using a global soil moisture monitoring program and a global database of karst spring discharges, we evaluate the simulations of a preliminary global karstic groundwater recharge model. We show that soil moisture is a crucial variable to better distinguish recharge dynamics in different climates and for different land cover types. Analyzing the global dataset, we find that mean discharge volumes, their variability and the recharge areas are showing similar variability for a large range of altitudes. Comparing the model simulations with the newly collected observations, indicates that (1) improvements of the recharge model are still necessary to obtain a better representation of different land cover types and snow processes, and (2) there is a need to incorporate groundwater dynamics. Applying and strictly evaluating these improvements in the model will finally provide a tool to identify hot spots of current or future water scarcity in the karst regions around the globe thus supporting national to international water governance.
Andreas Hartmann
added a research item
Groundwater pollution threatens human and ecosystem health in many areas around the globe. Shortcuts to the groundwater through concentrated recharge are known to transmit short-lived pollutants into carbonate aquifers endangering water quality of around a quarter of the world population. However, the large-scale impact of such concentrated recharge on water quality remains poorly understood. Here we apply a continental-scale model to quantify the danger of groundwater contamination by degradable pollutants through concentrated recharge in carbonate rock regions. We show that in regions where concentrated recharge takes place, the percentage of non-degraded pollutants in groundwater recharge increases from <1% to around 10-50%. In those regions, pollutants like Glyphosate can exceed their permissible concentrations by up to 19 times when reasonable application rates are assumed. Our results imply that in times of continuing industrial agricultural productivity, shortcuts to the groundwater may result in a widespread and substantial reduction of usable groundwater volumes.
Andreas Hartmann
added a research item
Karst groundwater constitutes a considerable fraction of drinking water in many regions in the world. Understanding its recharge processes is important for a sustainable water resource management. Experimental approaches to study karst aquifers mostly focus on the characterization of the entire aquifer using the disintegration of its output signal measured at the spring. Despite the important role of the soil and epikarst for recharge processes, limited attention has been given to this specific part of the systems. In our study, we present the first results of a soil monitoring program at five representative locations across the globe. We use a large number of soil moisture observations to understand the partitioning of rainfall into infiltration, storage, evapotranspiration, and groundwater recharge at five contrasting climates and two different land use types (forest & grassland).
Andreas Hartmann
added a research item
Karst aquifers provide drinking water for 10% of the world’s population, support agriculture, groundwater-dependent activities, and ecosystems. These aquifers are characterised by complex groundwater-flow systems, hence, they are extremely vulnerable and protecting them requires an in-depth understanding of the systems. Poor data accessibility has limited advances in karst research and realistic representation of karst processes in large-scale hydrological studies. In this study, we present World Karst Spring hydrograph (WoKaS) database, a community-wide effort to improve data accessibility. WoKaS is the first global karst springs discharge database with over 400 spring observations collected from articles, hydrological databases and researchers. The dataset’s coverage compares to the global distribution of carbonate rocks with some bias towards the latitudes of more developed countries. WoKaS database will ensure easy access to a large-sample of good quality datasets suitable for a wide range of applications: comparative studies, trend analysis and model evaluation. This database will largely contribute to research advancement in karst hydrology, supports karst groundwater management, and promotes international and interdisciplinary collaborations.
Tunde Olarinoye
added 2 research items
The hydrodynamics of karst aquifer depend largely on its strong heterogeneity which controls the flow signal of karstic springs. While there is much research in karst hydrology that focusses on local and catchment scales, comparative knowledge about the hydrodynamic behaviour of karst systems in different regions of the world and the understanding to parameterise karstification in ungauged basins remains limited. Finding an accurate descriptor of aquifer heterogeneity, its variation across different scales and regions of the world is still an open question in karst research. Springs enter undoubtedly well into the study of dynamic nature of karst aquifers because their flow behaviour reflects an integration of processes of what is happening within the entire karst groundwater basin. The characteristic behaviour of springs can be evaluated with global methods such as recession analysis that may provide quantitative information about the degree of karstification. Such quantitative measure would be of high value to compare karst spring behaviour at different catchment across the globe and reveal important information on factors that control the variability among karst systems under different climatic and physiographic conditions. This poster presents an overview of available data set, initial approach to the analysis, prospect methods and an outlook to the future applications of outcomes of this research.