[Show abstract][Hide abstract] ABSTRACT: Hydrologic interaction between surface and subsurface water systems has a significant impact on water quality, ecosystems and biogeochemistry cycling of both systems. Distributed models have been developed to simulate this function, but they require detailed spatial inputs and extensive computation time. The SWAT model is a semi-distributed model that has been successfully applied around the world. However it has not been able to simulate the two way exchanges between surface water and groundwater. In this study, the SWAT-LU model – based on a catena method that routes flow across three landscape units (the divide, the hillslope and the valley) – was modified and applied in the floodplain of the Garonne River. The modified model was called SWAT-LUD. Darcy's equation was applied to simulate groundwater flow. The algorithm for surface water level simulation during flooding periods was modified and the influence of flooding on groundwater levels was added to the model. Chloride was chosen as a conservative tracer to test simulated water exchanges. The simulated water exchange quantity from SWAT-LUD was compared with the output of a 2D distributed model, 2SWEM. The results showed that simulated groundwater levels in the LU adjoining the river matched the observed data very well. Additionally, SWAT-LUD model was able to reflect the actual water exchange between the river and the aquifer. It showed that river water discharge has a significant influence on the surface-groundwater exchanges. The main water flow direction in the river/groundwater interface was from groundwater to river, water flowed in this direction accounted for 65 % of the total exchanged water volume. The water mixing occurs mainly during high hydraulic periods. Flooded water was important for the SW-GW exchange process, it accounted for 69 % of total water flowed from the river to the aquifer. The new module also provides the option of simulating pollution transfer occurring at the river/groundwater interface at the catchment scale.
Full-text · Article · Jun 2016 · Hydrological Processes
[Show abstract][Hide abstract] ABSTRACT: SWAT, a watershed modeling tool has been proposed to help quantify ecosystem services. The concept of ecosystem services incorporates the collective benefits natural systems provide primarily to human beings. It is becoming increasingly important to track the impact that human activities have on the environment in order to determine its resilience and sustainability. The objectives of this paper are to provide an overview of efforts using SWAT to quantify ecosystem services, to determine the model’s capability examining various types of services, and to describe the approach used by various researchers. A literature review was conducted to identify studies in which SWAT was explicitly used for quantifying ecosystem services in terms of provisioning, regulating, supporting, and cultural aspects. A total of 44 peer reviewed publications were identified. Most of these used SWAT to quantify provisioning services (34%), regulating services (27%), or a combination of both (25%). While studies using SWAT for evaluating ecosystem services are limited(approximately 1% of SWAT’s peered review publications), and usage (vs. potential) of services by beneficiaries is a current model limitation, the available literature sets the stage for the continuous development and potential of SWAT as a methodological framework for quantifying ecosystem services to assist in decision-making.
[Show abstract][Hide abstract] ABSTRACT: Soil erosion threatens both soil and water resources and has increased globally due to the removal of natural vegetation and the intensification of existing agriculture. Brazil is privileged by a large proportion of natural vegetation and abundant freshwater. Recently, modifications of the Brazilian Forest Act (BFA) have been approved that offer landowners that had committed illegal riparian deforestation in the past amnesty from reforestation, and further reductions of riparian protected areas are currently discussed. Here, we used the Soil and Water Assessment Tool (SWAT) to simulate river discharge and sediment exports in a typical human-impacted Brazilian catchment, the Rio das Mortes catchment. By restoring the riparian vegetation according to the BFA and ignoring amnesties to land owners, the current annual sediment export of the catchment of 0.830 t ha−1 was reduced by 29.4% according to our model. Further, simulated reforestation twice the size demanded by the BFA resulted in a 31.4% reduction of the current sediment export. However, reforestation of 5 m homogeneous riparian corridor only, as currently discussed in the Federal Brazilian State of São Paulo, reduced sediment exports by only 23.8%, not considering expected additional erosion due to deforestation outside the simulated reforested 5 m corridor. Our study is the first catchment-wide assessment of the role of riparian vegetation in preventing soil erosion in Brazil. Its results support intensive reforestation efforts of the riparian zone and point to substantial negative effects of further reductions of the protected riparian corridor width and amnesties from reforestation to land owners.
[Show abstract][Hide abstract] ABSTRACT: The Soil and Water Assessment Tool (SWAT) is one of the most widely used watershed models for simulating hydrology in response to agricultural management practices. However, limited studies have been performed to evaluate the SWAT model's ability to estimate daily and monthly evapotranspiration (ET) in semiarid regions. ET values were simulated using ArcSWAT 2012 for a lysimeter field managed under dryland conditions at the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas, and compared with measured lysimeter values from 2000 to 2010. Two scenarios were performed to compare SWAT's performance: (1) use of default plant leaf area index (LAI) values in the embedded plant database and (2) adjusted LAI values. Scenario 1 resulted in an "unsatisfactory" Nash-Sutcliffe efficiency (NSE) of 0.42 and 0.38 for the calibration and validation periods, respectively. Scenario 2 resulted in a "satisfactory" NSE value for the calibration period while achieving a "good" NSE of 0.70 for the validation period. SWAT generally underestimated ET at both the daily and monthly levels. Overestimation during fallow years may be due to the limitations of the pothole function used to simulate furrow diking. Users should be aware of potential errors associated with using default LAI parameters. Inaccuracies in ET estimation may also stem from errors in the plant stress functions, particularly when evaluating water management practices for dryland watersheds.
Full-text · Article · Jan 2016 · Journal - American Water Works Association
[Show abstract][Hide abstract] ABSTRACT: Failure to set up a large-scale hydrological model correctly may not allow proper calibration and uncertainty analyses, leading to inaccurate model prediction. To build a model with accurate accounting of hydrological processes, a data discrimination procedure was applied in this study. The framework uses a hydrological model of Alberta built with the Soil and Water Assessment Tool (SWAT) program. The model was used to quantify the causes and extents of biases in predictions due to different types of input data. Data types represented different sources of errors, including input data (e.g., climate), conceptual model (e.g., potholes, glaciers), and control structure (e.g., reservoirs, dams). The results showed that accounting for these measures leads to a better physical accounting of hydrological processes, significantly improving the overall model performance. The procedure used in this study helps to avoid unnecessary and arbitrary adjustment of parameters to compensate for the errors in the model structure.
Full-text · Article · Dec 2015 · Environmental Modelling and Software
[Show abstract][Hide abstract] ABSTRACT: The Missouri River Basin (MRB) is the largest river basin in the U. S. and is one of the most important agricultural regions in the world. Three decadal climate variability (DCV) phenomena - the Pacific Decadal Oscillation (PDO), the tropical Atlantic sea-surface temperature (SST) gradient variability (TAG for brevity), and the West Pacific Warm Pool (WPWP) SST variability – substantially influence hydro-meteorology in the MRB. We report on a simulation study with the Soil and Water Assessment Tool (SWAT) to estimate impacts on water availability in response to realistic values of PDO, TAG, and WPWP indices in approximately 13,500 hydrologic unit areas covering the MRB. SWAT, driven by hydro-meteorological anomalies associated with positive and negative phases of PDO and TAG, indicated major impacts on water yields and streamflows, as much as ±40% of the average in many locations. Impacts of the WPWP index variability were smaller. Consistent with observations during 1949 to 2010, SWAT showed water flow increases of as much as 80% of the average causing very wet periods when the positive phase of the PDO and the negative phase of the TAG at extreme amplitudes were superposed. Water flows decreased by a similar amount resulting in severe to extreme droughts when the negative phase of the PDO and the positive phase of the TAG at extreme amplitudes were superposed. Thus, the combined and cumulative effects of these DCV phenomena on water flows, droughts, and wet periods in the MRB can be dramatic with important consequences for all water-consuming sectors as well as for feedbacks to the climate system.
No preview · Article · Nov 2015 · Journal of Hydrometeorology
[Show abstract][Hide abstract] ABSTRACT: Assessment of long-term anthropogenic impacts on agro-ecosystems requires comprehensive modelling capabilities to simulate water interactions between the surface and groundwater domains. To address this need, a modelling framework, called " SWATmf " , was developed to link and integrate the Soil Water Assessment Tool (SWAT), a widely used surface watershed model with the MODFLOW, a groundwater model. The SWATmf is designed to serve as a project manager, builder, and model performance evaluator, and to facilitate dynamic interactions between surface and groundwater domains at the watershed scale, thus providing a platform for simulating surface and groundwater interactions. Using datasets from the Fort Cobb Reservoir experimental watershed (located in Oklahoma, USA), the SWATmf to facilitate linkage and dynamic simulation of SWAT and MODFLOW models. Simulated streamflow and groundwater levels generally agreed with observations trends showing that the SWATmf can be used for simulating surface and groundwater interactions.
Full-text · Article · Nov 2015 · Environmental Modelling and Software
[Show abstract][Hide abstract] ABSTRACT: Water harvesting systems have improved productivity in various regions in sub-Saharan Africa. Similarly, they can help retain water in landscapes, build resilience against droughts and dry spells, and thereby contribute to sustainable agricultural intensification. However, there is no strong empirical evidence that shows the effects of intensification of water harvesting on upstream–downstream social–ecological systems at a landscape scale. In this paper we develop a decision support system (DSS) for locating and sizing water harvesting ponds in a hydrological model, which enables assessments of water harvesting intensification on upstream–downstream ecosystem services in meso-scale watersheds. The DSS was used with the Soil and Water Assessment Tool (SWAT) for a case-study area located in the Lake Tana basin, Ethiopia. We found that supplementary irrigation in combination with nutrient application increased simulated teff (Eragrostis tef, staple crop in Ethiopia) production up to three times, compared to the current practice. Moreover, after supplemental irrigation of teff, the excess water was used for dry season onion production of 7.66 t/ha (median). Water harvesting, therefore, can play an important role in increasing local- to regional-scale food security through increased and more stable food production and generation of extra income from the sale of cash crops. The annual total irrigation water consumption was ~ 4%–30% of the annual water yield from the entire watershed. In general, water harvesting resulted in a reduction in peak flows and an increase in low flows. Water harvesting substantially reduced sediment yield leaving the watershed. The beneficiaries of water harvesting ponds may benefit from increases in agricultural production. The downstream social–ecological systems may benefit from reduced food prices, reduced flooding damages, and reduced sediment influxes, as well as enhancements in low flows and water quality. The benefits of water harvesting warrant economic feasibility studies and detailed analyses of its ecological impacts.
Full-text · Article · Oct 2015 · Science of The Total Environment
[Show abstract][Hide abstract] ABSTRACT: The Upper Trinity River Basin (TRB) is the most populated river basin and one of the largest water suppliers in Texas. However, sediment and nutrient loads are reducing the capacity of reservoirs and degrading water quality. The objectives of this study are to calibrate and validate the Soil and Water Assessment Tool (SWAT) model for ten study watersheds within the Upper TRB in order to assess nutrient loads into major reservoirs in the basin and to predict the effects of point source elimination and urbanization on nutrient loads through scenario analyses. SWAT performed reasonably well for the current condition except for two out of five tributaries in the Eagle Mountain watershed and total phosphorous in Richland-Chambers. The impacts of simulated scenarios varied within watersheds. Point-source elimination achieved reductions ranging from 0.3% to 24% in total phosphorus and 1% to 56% in total nitrogen received by the reservoirs. Population and development projections were used to examine the impacts of urbanization on each watershed. Projected urbanization in 2030 had large effects on simulated total phosphorus loads in some watersheds, ranging from a reduction of 1% to an increase of 111%. Projected urbanization also affected simulated total nitrogen loads, from a reduction of 3% to an increase of 24%. One limitation of this study is the lack of long-term, up-to-date water quality data due to discontinued water-quality monitoring stations. Although careful considerations were given to the adjustment of parameter values reflecting various aspects of the nutrient processes, further data collection will enhance modeling study for assessment of these watersheds' water resources and environmental problem.
[Show abstract][Hide abstract] ABSTRACT: Here, we compared grid precipitation data–Climate Forecast System Reanalysis (CFSR) and WATCH Forcing Data methodology applied to ERA-Interim (WFDEI) data–with Brazilian Weather Bureau (INMET) and Brazilian Water Agency (ANA) rain gauge data (n = 2027) for the period 1980–2010 in order to evaluate which grid data set better represents precipitation, and is thus more suitable for hydrological modelling of Brazilian water resources. We found that WFDEI outperformed CFSR according to three statistical indicators. We then applied and interpolated a simple bias correction to further improve WFDEI data before we used these data to model river discharge of the Tocantins catchment with the Soil and Water Assessment Tool (SWAT). Calibration (validation in parentheses; weighted averages of all gauges) had satisfactory statistical metrics: p-factor = 0.52 (0.47); r-factor = 0.84 (0.99); R2 = 0.78 (0.71); bR2 = 0.68 (0.47); NS = 0.70 (0.66); Pbias = −4.5 (4.0). Finally, the calibrated SWAT model was used to assess the spatial distribution of the catchment's water resources. Annual green water flow (evapotranspiration) increased from the south-east (640–840 mm yr−1) to north-west (1140–1440 mm) of the Tocantins catchment, while green water storage (soil water content) increased from south (330–1070 mm) to north (2180–3290 mm). Blue water (water yield) had a less clear pattern, with lower values in the south and the central borders of the catchment (20–560 mm) and higher values along the central axis and the north (920–1460 mm). Our analysis suggested that WFDEI was an accurate representation of Brazilian precipitation. For large catchments, we therefore recommend the use of WFDEI instead of sparse and often missing rain gauge data in modelling Brazilian water resources. This article is protected by copyright. All rights reserved.
Full-text · Article · Oct 2015 · Hydrological Processes
[Show abstract][Hide abstract] ABSTRACT: The Soil and Water Assessment Tool (SWAT) model has been applied widely in many types of environment with different goals. The purpose of this paper is to assess the ability of SWAT to simulate hydrological processes in the Aixola watershed. Electrical conductivity (EC) was used to estimate water contribution from the two main sub-watersheds. Streamflow contribution from the sub-watersheds varies throughout the year; the larger of the two contributes greater flow in wetter seasons, while the smaller one has more regulation capacity and contributes more in summer. The data obtained from EC were used to calibrate the model, simulating this variability satisfactorily and even more-so when the model was forced during calibration. Additionally, EC measured at the outlet of the watershed was used to make a decomposition of the hydrograph (surface runoff – base flow), comparing the data obtained with those simulated by SWAT. The results showed that the model performed well and identified the source of uncertainties in modelling this watershed. When additional data is included in the calibration, this made it possible to obtain a more realistic hydrological simulation of the Aixola watershed.
No preview · Article · Jun 2015 · Journal of Hydrology
[Show abstract][Hide abstract] ABSTRACT: Soil erosion threatens both soil and water resources and has increases globally due to changes in land use, mainly the substitution of natural vegetation by agricultural crops and pasture, or the intensification of existing agriculture. Brazil is privileged by a large proportion of natural vegetation and abundant freshwater. Recently, a new Brazilian Forest Act (BFA) has been approved that offers landowners that had committed illegal riparian deforestation in the past amnesty from reforestation, and further reductions of riparian protected areas are currently discussed. Here. we used the Soil and Water Assessment Tool (SWAT) to simulate river discharge and sediment exports in a typical human-impacted Brazilian catchment, the Rio das Mortes Basin in the Federal State of Minas Gerais. Our model simulated different scenarios of riparian zone reforestation and their benefits in reducing sediment exports. By restoring the riparian vegetation according to the BFA ignoring amnesties to land owners (i.e. 44.8% of the 200 km2 legal riparian corridor of the river, with a corridor width of 30-50 m), the current annual sediment yield of the catchment of 0.819 t ha-1 was reduced in 34%. Further, simulated reforestation twice the size demanded by the BFA (60-100 m corridor width) resulted by 34.8% reduction of the current sediment yield. However, reforestation of 5 m homogeneous riparian corridor only, as currently discussed in the Federal Brazilian State of São Paulo, reduced sediment exports by 28%, not considering expected additional erosion due to deforestation outside the simulated reforested 5 m corridor. Our study is the first basin-wide assessment of the role of riparian vegetation in preventing soil erosion in Brazil. Its results support intensive reforestation efforts of the riparian zone and point to substantial negative effects of further reductions of the protected riparian corridor width and amnesties from reforestation to land owners.
[Show abstract][Hide abstract] ABSTRACT: Impact of climate change on the water resources of the United States exposes the vulnerability of feedstock-specific mandated fuel targets to extreme weather conditions that could become more frequent and intensify in the future. Consequently, a sustainable biofuel policy should consider: (a) how climate change would alter both water supply and demand; and (b) in turn, how related changes in water availability will impact the production of biofuel crops; and (c) the environmental implications of large scale biofuel productions. Understanding the role of biofuels in the water cycle is the key to understanding many of the environmental impacts of biofuels. Therefore, the focus of this study is to model the rarely explored interactions between land use, climate change, water resources and the environment in future biofuel production systems. Results from this study will help explore the impacts of the US biofuel policy and climate change on water and agricultural resources. We used the Soil and Water Assessment Tool (SWAT) to analyze the water quantity and quality consequences of land use and land management related changes in cropping conditions (e.g., more use of marginal lands, greater residue harvest, increased yields), plus management practices due to biofuel crops to meet the Renewable Fuel Standard target on water quality and quantity.
[Show abstract][Hide abstract] ABSTRACT: The acquisition of adequate weather data is the most challenging task when setting up a hydrologic model. While vegetation, soil and topographic information can be newly assessed if not available, weather data are needed as extensive time series. In our study, we analysed CFSR and WFDEI precipitation data in comparison to rain gauges in the Brazilian territory (n = 2027) for the period 1980-2010 to evaluate which weather reanalysis better represented precipitation in Brazil. Further, we used monthly-based interpolations (and historic monthly averages to fill gaps in time series) to further improve the best data set to measured precipitation. We then applied the interpolated precipitation in the river discharge modelling of the Tocantins Basin with the Soil and Water Assessment Tool (SWAT). Both reanalyses showed better statistics for monthly series than for daily and annual series. WFDEI better represented Brazilian precipitation than CFSR with higher coefficient of determination (R2 = 0.76 vs. 0.50; medians), coefficient of determination multiplied by the coefficient of the regression (bR2 = 0.70 vs. 0.39) and Nash-Sutcliffe coefficient (NS = 0.72 vs. 0.21), but equal percentages of bias (Pbias = 6.9 vs. 3.4). We applied interpolated WFDEI precipitation data in the hydrologic model of the Tocantins Basin with SWAT using 7 river gauges and 3 reservoirs, with an NS > 0.60 for 6 out of 10 stations (NS = 0.19, 0.38, 0.39 and 0.44 for the other 4 stations). Green water flow increased from South-East (640-840 mm) to North-West (1140-1440 mm), while green water storage increased from South (330-1070 mm) to North (2180-3290 mm). Blue water had a less clear pattern, with lower values in the South and central borders of the basin (20-560 mm) and higher values in the central axis and the North (920-1460 mm). Our analysis suggested that WFDEI was an accurate representation of Brazilian precipitation and allowed for the use of reanalysis weather data instead of observational data in hydrologic modelling.