Climate change impacts on hydrologic components and occurrence of drought in an agricultural watershed
The study on potential acceleration of future hydrologic cycle due to change in precipitation and increase in temperature are essential for managing natural resources and setting policy. The impact of future climate change on hydrologic components of Goodwater Creek Experimental Watershed (GCEW) and experimental field (Field1) were assessed using climate datasets from the Coupled Model Intercomparison Project Phase 5 (CMIP5), Soil and Water Assessment Tool (SWAT) and Agricultural Policy Environmental Extender (APEX). SWAT and APEX models were setup and calibrated for watershed and field scale using observed hydrology data at their respective outlets. The study identified future (2016-2075) occurrence of meteorological, hydrological, agricultural droughts, and extreme events based on projections of future climate in the GCEW and SWAT simulations. Standardized Precipitation Index, Standardized Streamflow Index, and Soil Moisture Index were used to represent the three types of drought. CMIP5 data were downscaled to watershed and field scale using quantile mapping for precipitation and delta method for temperature. Historical and future ensembles of downscaled precipitation and temperature, and modeled water yield, surface runoff, and evapotranspiration were compared. At the watershed scale, ensemble SWAT simulated results indicated increased springtime precipitation, water yield, surface runoff and a shift in evapotranspiration peak one month earlier in the future. At field scale, two management system business-As-Usual (BAU) and Aspirational (ASP) management system were compared to access the environmental benefits of improved management system using APEX model. Simulated results indicated that the change in management alone from BAU to ASP during historic period resulted in 25% (162 mm to 120 mm) reduction in surface runoff. The simulated average annual runoff loss was reduced by 16.5% (192 mm to 160 mm) and 18.8% (203 mm to 165 mm) in ASP scenario compared to BAU for ensemble of RCP 8.5 for near and far future respectively. The average ensemble annual soluble nitrogen loss was 8 kg/ha for BAU compared to 3.9 kg/ha for ASP management for baseline historic period. Result indicated the inclusion of no-till and winter cover crop resulted in increased subsurface flow. The result indicates the environmental benefit of crop rotation and cover crop with reduction in runoff and nutrient losses. The ASP management provides surface cover all year round and improves soil quality resulting in lower runoff.
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