Soil andWater Assessment Research Articles

An extensible schema for capturing environmental model metadata: Implementation in the HydroShare online data repository

Model metadata can be used to document the specifications, inputs, provenance, and other important attributes of an environmental modeling application. An open challenge in creating a general model metadata schema is addressing the diversity of environmental models in a way that provides flexibility and scalability while maintaining a standard core. This paper presents a new model metadata schema design aimed at addressing this challenge. Specifically, we present an extensible metadata schema for describing what we call a model instance: a specific application of an environmental model. We implement the schema in the HydroShare online data repository and demonstrate how the schema can be used for the Soil and Water Assessment (SWAT) model.

NSP variation on SWAT with high-resolution data: A case study

Abstract As a typical lake in the early stage of eutrophication, the non-point source pollution (NSP) in Erhai Lake was highly concerned. Since 2017, protection and rescue actions have been implemented in the Erhai Lake basin which significantly improved the water quality of Erhai Lake. But little attention has been paid to the interception effects of these actions on NSP. Based on high resolution datasets, including refinement land use/land cover (LU/LC) data, China Meteorological Assimilation Driving Database for the SWAT (CMADS), and Advanced Land Observing Satellite-1 (ALOS-12) data, the interception effects of ecological ponds newly built in 2018 on NSP was discussed with the support of the soil and water assessment (SWAT) model. These three high resolution datasets can meet the needs for simulating NSP by SWAT model, which was conductive to better reveal the interception effects of ecological ponds on NSP. Besides, the pollution load of shrubbery on Total nitrogen (TN)/Total phosphorous (TP), which has never been involved in similar research works in the Erhai Lake basin, was measured. Compared the temporal and spatial variations in TN/TP concentration before and after 2018, the interception effects of ecological ponds on NSP in the Erhai Lake basin were revealed by a sharp decrease in TN/TP concentration and a delayed presence of annual peak value about 1 month late in TN concentration before and after 2018. The interception intensity of NSP was determined by the number and volume of ecological ponds in each sub-basin and their corresponding upstream.

Adapting reservoir operation rules to hydrological drought state and environmental flow requirements

Negligence of environmental flow (e-flow) has severe adverse impacts on wetlands. Additionally, hydrological droughts, compounded by mismanagement of available water resources and anthropogenic activities, lead to water shortage and degrade wetland ecosystem. However, in dealing with reservoir operation/re-operation, a few studies have addressed inflow uncertainty and hydrological drought state to improve the monthly operation performance of an upstream reservoir in coordination with downstream wetland needs. Hence, the study objective is to adopt a linear/nonlinear reservoir operation rule to hydrological drought states and e-flow requirements. So, first, the soil and water assessment (SWAT) model is applied to simulate the natural daily flow regime by eliminating human impacts. Then, using the Tennant e-flow scheme, the intra/inter-annual variability of e-flow and the degree of alteration of the flow are measured. Afterward, using the Standardized Hydrological Drought Index (SHDI), the drought/wet severity and duration are determined. A linear/nonlinear simulation model adopted for the presentation of reservoir policies and the non-dominated sorting genetic algorithm-II (NSGA-II) was employed to determine the optimal monthly operation of the upstream reservoir. The simulated operation policies correspond to each hydrological drought state were evaluated with reliability, resilience, vulnerability, and water-deficit indices. Results indicated that incorporation of hydrological drought state could improve the overall system reliability by 23% over simply enforcing the monthly variable-parameter nonlinear decision rules. Also, the proposed methodology simultaneously maximized the downstream allocated water and e-flow of the terminal wetland. It also implicitly minimized the change in extreme flow metrics that are known to benefit ecosystem diversity. The proposed framework supports reservoir re-operation in regions subject to challenges in supplying water to different sectors while maintaining e-flow during drought periods.

Hydrological Extremes and Responses to Climate Change in the Kelantan River Basin, Malaysia, Based on the CMIP6 HighResMIP Experiments

This study introduces a hydro-climatic extremes assessment framework that combines the latest climate simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) HighResMIP with the Soil and Water Assessment (SWAT) model, and examines the influence of the different climate model resolutions. Sixty-six hydrological and environmental flow indicators from the Indicators of Hydrologic Alteration (IHA) were computed to assess future extreme flows in the Kelantan River Basin (KRB), Malaysia, which is particularly vulnerable to flooding. Results show that the annual precipitation, streamflow, maximum and minimum temperatures are projected to increase by 6.9%, 9.9%, 0.8 °C and 0.9 °C, respectively, by the 2021–2050 period relative to the 1985–2014 baseline. Monthly precipitation and streamflow are projected to increase especially for the Southwest Monsoon (June–September) and the early phase of the Northeast Monsoon (December) periods. The magnitudes of the 1-, 3-, 7-, 30- and 90-day minima flows are projected to increase by 7.2% to 8.2% and the maxima flows by 10.4% to 28.4%, respectively. Lastly, changes in future hydro-climatic extremes are frequently quite different between the high-resolution and low-resolution models, e.g., the high-resolution models projected an increase of 11.8% in mean monthly flow in November-December-January compared to 3.2% for the low-resolution models.

Assessing Climate Change Effects on Water Balance in a Monsoon Watershed

Understanding the changes on future water resources resulting from climate variations will assist in developing effective management strategies for a river basin. Our area of interest is the Osan watershed in South Korea, where the summer monsoon contributes approximately 60–70% of the annual runoff and precipitation for the country. We determined the effects that future climatic changes have on this area. To accomplish this, we made use of global climate models (GCMs). A total of 10 GCMs were downscaled with the help of climate information production tools. Coupled with the GCMs and the Soil and Water Assessment (SWAT) model, three periods were used to assess these climate impacts. The baseline, mid-century (MC), and end-century (EC) periods include 1993–2018, 2046–2065, and 2081–2099, respectively. The entire process was performed using two scenarios (4.5 and 8.5) from the representative concentration pathways (RCPs). Some of the statistical metrics used for model calibration and validation were p-factor, r-factor, percent bias, root-mean-square error (RMSE), and Nash–Sutcliffe model efficiency. Their respective values were 0.88, 0.88, 8.3, 0.91, and 0.91 for calibration, and 1.16, 0.85, 7.9, 0.88, and 0.87 for validation. For the MC and EC periods under both scenarios, we projected an increase in temperature and precipitation of approximately 2–5 °C and 15–30%, respectively. A predicted rise in precipitation, surface flow, lateral flow, and water yield were noted for the month of June. Subsequently, a decline in July followed during the summer monsoon season. Summer monsoon rains will fluctuate more sharply, with heavy rainfall in June, lower rainfall in July, and more rain in the late summer, leading to the possibility of both flooding and drought within a given period. Annual precipitation, surface flow, lateral flow, and water yield will increase whereas evapotranspiration would decrease in both periods under both scenarios during the summer monsoon period, which will lead to wetter conditions in the future.

Multi-Variable Sensitivity Analysis, Calibration, and Validation of a Field-Scale SWAT Model: Building Stakeholder Trust in Hydrologic and Water Quality Modeling

HighlightsSWAT can adequately simulate runoff, soil moisture, cotton and peanut yields, and nitrate at field scale.Muskingum routing and adjusting DIS_STREAM are important to simulate fields as watersheds rather than HRUs.Crop yield calibration is critical for improving SWAT model robustness in nutrient transport simulations and for building stakeholder trust.SWAT can quantify the impacts of different management scenarios at the field scale.Abstract. Multi-variable calibration of a field-scale Soil and Water Assessment (SWAT) model is critical for understanding the true impacts of irrigation and nutrient best management practices (BMPs) on hydrology, water quality, and agricultural productivity and for building stakeholder trust for eventual BMP implementation at the watershed scale. This study evaluated the ability of SWAT to simulate runoff, soil moisture, cotton and peanut yields, and nitrate in conventionally tilled and strip-tilled plots while also evaluating the differences in hydrological and nutrient simulation parameters for the two tillage practices. Modeling results showed that SWAT adequately simulated runoff, soil moisture, cotton and peanut yields, and nitrate at the field scale and that calibrated values for the curve number of operation (CNOP) were different for the conventionally tilled and strip-tilled plots and critical to runoff calibration. It was also important to change the routing method from variable storage to Muskingum and to adjust DIS_STREAM for runoff simulation if the field was to be simulated as a watershed rather than as an HRU. Sequential calibration of surface runoff, soil moisture, crop yield, and nitrate showed that crop yield can be an important consideration for improving SWAT model robustness in nutrient transport simulations. Soil moisture calibration did not have a significant effect on runoff simulations. Evaluation of the impacts of different management scenarios showed that soil moisture sensor-based irrigation, cover crop, and strip tillage had the highest potential for reducing nutrient loss and conserving water while maintaining agricultural productivity in southern Georgia. This study also demonstrated to stakeholders that the SWAT model can successfully quantify the impacts of different management scenarios on their farm fields. Keywords: Agricultural BMPs, Field-scale SWAT, Multi-variable calibration, SWAT, SWAT-CUP.

A comprehensive sensitivity and uncertainty analysis for discharge and nitrate-nitrogen loads involving multiple discrete model inputs under future changing conditions

Abstract. Environmental modeling studies aim to infer the impacts on environmental variables that are caused by natural and human-induced changes in environmental systems. Changes in environmental systems are typically implemented as discrete scenarios in environmental models to simulate environmental variables under changing conditions. The scenario development of a model input usually involves several data sources and perhaps other models, which are potential sources of uncertainty. The setup and the parametrization of the implemented environmental model are additional sources of uncertainty for the simulation of environmental variables. Yet to draw well-informed conclusions from the model simulations it is essential to identify the dominant sources of uncertainty. In impact studies in two Austrian catchments the eco-hydrological model Soil and Water Assessment Tool (SWAT) was applied to simulate discharge and nitrate-nitrogen (NO3--N) loads under future changing conditions. For both catchments the SWAT model was set up with different spatial aggregations. Non-unique model parameter sets were identified that adequately reproduced observations of discharge and NO3--N loads. We developed scenarios of future changes for land use, point source emissions, and climate and implemented the scenario realizations in the different SWAT model setups with different model parametrizations, which resulted in 7000 combinations of scenarios and model setups for both catchments. With all model combinations we simulated daily discharge and NO3--N loads at the catchment outlets. The analysis of the 7000 generated model combinations of both case studies had two main goals: (i) to identify the dominant controls on the simulation of discharge and NO3--N loads in the two case studies and (ii) to assess how the considered inputs control the simulation of discharge and NO3--N loads. To assess the impact of the input scenarios, the model setup, and the parametrization on the simulation of discharge and NO3--N loads, we employed methods of global sensitivity analysis (GSA). The uncertainties in the simulation of discharge and NO3--N loads that resulted from the 7000 SWAT model combinations were evaluated visually. We present approaches for the visualization of the simulation uncertainties that support the diagnosis of how the analyzed inputs affected the simulation of discharge and NO3--N loads. Based on the GSA we identified climate change and the model parametrization as being the most influential model inputs for the simulation of discharge and NO3--N loads in both case studies. In contrast, the impact of the model setup on the simulation of discharge and NO3--N loads was low, and the changes in land use and point source emissions were found to have the lowest impact on the simulated discharge and NO3--N loads. The visual analysis of the uncertainty bands illustrated that the deviations in precipitation of the different climate scenarios to historic records dominated the changes in simulation outputs, while the differences in air temperature showed no considerable impact.

Implications of water management representations for watershed hydrologic modeling in the Yakima River basin

Abstract. Water management substantially alters natural regimes of streamflow through modifying retention time and water exchanges among different components of the terrestrial water cycle. Accurate simulation of water cycling in intensively managed watersheds, such as the Yakima River basin (YRB) in the Pacific Northwest of the US, faces challenges in reliably characterizing influences of management practices (e.g., reservoir operation and cropland irrigation) on the watershed hydrology. Using the Soil and Water Assessment Tool (SWAT) model, we evaluated streamflow simulations in the YRB based on different reservoir operation and irrigation schemes. Simulated streamflow with the reservoir operation scheme optimized by the RiverWare model better reproduced measured streamflow than the simulation using the default SWAT reservoir operation scheme. Scenarios with irrigation practices demonstrated higher water losses through evapotranspiration (ET) and matched benchmark data better than the scenario that only considered reservoir operations. Results of this study highlight the importance of reliably representing reservoir operations and irrigation management for credible modeling of watershed hydrology. The methods and findings presented here hold promise to enhance water resources assessment that can be applied to other intensively managed watersheds.

Assessing model parameters sensitivity and uncertainty of streamflow, sediment, and nutrient transport using SWAT

The objectives of this study were to (1) simulate streamflow, total sediment (TS), total phosphorus (TP), and total nitrogen (TN) loads; and (2) use the sequential uncertainty fitting (SUFI-2) algorithm to quantify the model parameter sensitivity and uncertainty in simulating streamflow, TS, TP, and TN loads using Soil and Water Assessment (SWAT) model in Big Sunflower River watershed (BSRW). The model was calibrated from 1996 to 2003 and validated from 2004 to 2010 for daily streamflow, TS load, TP load, and TN load. The model performed well simulating daily streamflow (R2 = 0.58–0.75, NSE = 0.47–0.75), TS load (R2 = 0.50–0.72, NSE = 0.47–0.66), and TP load (R2 = 0.79–0.82, NSE = 0.73–0.77), and the model performance was slightly low for TN load (R2 = 0.13–0.31, NSE = −0.09 to 0.07). This study determined that parameter uncertainty was greatest for simulating TN load (p-factor = 0.48, r-factor = 1.25) and that parameter uncertainty was lowest for simulating streamflow (p-factor = 0.70–0.78, r-factor = 1.18–1.19). Output uncertainty was much greater during peak streamflow and peak pollutant loads compared to periods of low streamflow and low pollutant loads. The sensitivity analyses found that streamflow was most sensitive to Manning’s roughness coefficient for the main channel (CH_N2), TS load was most sensitive the peak rate adjustment factor for sediment routing in the tributary channels (ADJ_PKR), TP load was most sensitive to the Phosphorus enrichment ratio for loading with sediments (ERORGP), and TN load was most sensitive to the denitrification exponential rate coefficient (CDN). Uncertainty was found to be much greater during peak streamflow and peak pollutant loads compared to periods of low streamflow and low pollutant loads.

Multimodel assessment of climate change-induced hydrologic impacts for a Mediterranean catchment

Abstract. This work addresses the impact of climate change on the hydrology of a catchment in the Mediterranean, a region that is highly susceptible to variations in rainfall and other components of the water budget. The assessment is based on a comparison of responses obtained from five hydrologic models implemented for the Rio Mannu catchment in southern Sardinia (Italy). The examined models – CATchment HYdrology (CATHY), Soil and Water Assessment Tool (SWAT), TOPographic Kinematic APproximation and Integration (TOPKAPI), TIN-based Real time Integrated Basin Simulator (tRIBS), and WAter balance SImulation Model (WASIM) – are all distributed hydrologic models but differ greatly in their representation of terrain features and physical processes and in their numerical complexity. After calibration and validation, the models were forced with bias-corrected, downscaled outputs of four combinations of global and regional climate models in a reference (1971–2000) and future (2041–2070) period under a single emission scenario. Climate forcing variations and the structure of the hydrologic models influence the different components of the catchment response. Three water availability response variables – discharge, soil water content, and actual evapotranspiration – are analyzed. Simulation results from all five hydrologic models show for the future period decreasing mean annual streamflow and soil water content at 1 m depth. Actual evapotranspiration in the future will diminish according to four of the five models due to drier soil conditions. Despite their significant differences, the five hydrologic models responded similarly to the reduced precipitation and increased temperatures predicted by the climate models, and lend strong support to a future scenario of increased water shortages for this region of the Mediterranean basin. The multimodel framework adopted for this study allows estimation of the agreement between the five hydrologic models and between the four climate models. Pairwise comparison of the climate and hydrologic models is shown for the reference and future periods using a recently proposed metric that scales the Pearson correlation coefficient with a factor that accounts for systematic differences between datasets. The results from this analysis reflect the key structural differences between the hydrologic models, such as a representation of both vertical and lateral subsurface flow (CATHY, TOPKAPI, and tRIBS) and a detailed treatment of vegetation processes (SWAT and WASIM).

INFLUENCE OF LAND USE CHANGE ON SEDIMENT YIELD: A CASE STUDY OF THE SUB-MIDDLE OF THE SÃO Francisco River Basin

ABTSRACT Erosion risk mapping and assessment are important for planning of natural resource management tool. The objective of this study was to simulate different scenarios of land use in the Sub-Middle of the São Francisco River Basin using the Soil and Water Assessment (SWAT) model to analyze the effects of changes in sediment yield, making comparisons with the present land use classification. The scenario analysis was (i) vegetation type characteristic of the semiarid region, (ii) growing corn and (iii) bare soil. For calibration procedure, the first three years of time series from 1993 to 1994 were validated using data from 1995 to 2004. The SWAT model employs the Modified Universal Soil Loss Equation (MUSLE) to compute soil erosion data. The results of simulations for different land uses allowed the identification of areas with a high potential for erosion by water. The major impact produced by sediment inflow was in the bare soil scenario, corresponding to an increase of 93.7% over the current land use. The landscape management in river basins using SWAT model can help identify areas particularly susceptible to erosion process.

Impact of climate change on hydrology of Manjalar sub basin of river Vaigai in Tamil Nadu, India

This study evaluates the impacts of possible future climate change scenarios on the hydrology of the catchment area of the Manjalar sub basin of River Vaigai, Tamil Nadu, India carried out at the department of Soil and Water Conservation Engineering, Tamil Nadu Agricultural University during the period of 2011-2014 using Soiland Water Assessment Tool (SWAT). For the climate impact assessment the hydrological model was driven with output of bias corrected Earth System Models of the Coupled Model Intercomparison Project Phase 5 (CMIP5): HadGEM2. Climate scenarios were downscaled to a grid resolution of 0.22° x 0.22°. In this study RCP 4.5 and RCP 8.5 were included for future assessment with three future periods: 2012–2039, 2040–2069, and 2070–2098. The projected increase in maximum and minimum temperature for RCP 4.5 scenario is 0.8 to 2.3 ºC and 0.7 to 1.6 ºC and for RCP 8.5 scenario is 1.1 to 4.0 ºC and 1.0 to 3.1 ºC, respectively. Rainfall is projected to an increase between 9.2 to 15.2 per cent for RCP 4.5 scenario and an increase of 13.6 to 18.8 per cent for RCP 8.5 scenario during 21st century. The soil water storage and stream flow contribution to ground water are likely to increase in RCP 4.5 scenario and it would again decline for RCP 8.5 scenario during 21st century. The increase in annual rainfall evapotranspiration and surface runoff would be more in RCP 8.5 scenario compared to RCP 4.5 scenario. The possible changes projected by the study provide a useful input to effective planning of water resources of the study area.

Hydrologic model for design and constructed wetlands

The Trinity River Mitigation Bank was proposed to develop and use a mature, contiguous, diverse riparian corridor along the West Fork of the Trinity River near Dallas, Texas, USA. In the proposed wetland design, water would be diverted from Walker Creek as necessary to maintain wetland function. Therefore, assessment of the magnitude and continuity of the flow from Walker Creek was paramount to successful wetland operation. The Soil and Water Assessment (SWAT) model was used to assess whether the sustained flow (storm flow and base flow) from the Walker Creek Basin could maintain the proposed bottomland wetland ecosystem. For this study, SWAT was modified to allow ponded water within the prescribed wetland to interact with the soil profile and the shallow aquifer. The water budget was prepared for the wetland based on a three-step process. First, data required to run the model on Walker Creek, including soils, topographic, land-use, and daily weather data were assembled. Next, data required to validate the model were obtained. Since stream flow was not available at the proposed site, flow from a nearby watershed with similar soils, land use and topography were used. In the final step, the model was run for 14 years and compared to the measured water balance at the nearby watershed. The model results indicate that the wetland should be at or above 85 percent capacity over 60 percent of the time. The wetland did not dry up during the entire simulated time period (14 years) and reached 40 percent capacity less than one percent of the time during the simulation period. The advantages of the continuous simulation approach used in this study include (1) validation of wetland function (hydroperiod, soil water storage, plant water uptake) over a range of climatic conditions and (2) the ability to assess the long-term impact of land-use and management changes.