Evaluating Best Management Practices (BMPs) in watersheds using hydrologic and water quality models can help to establish an effective watershed water management. Soil and Water Assessment Tool (SWAT) was applied to Big Sunflower River Watershed (BSRW) and the Stovall Sherard Watershed (SSW) to evaluate BMP’s impact at watershed and field scale watersheds respectively. SWAT was calibrated and validated for streamflow, sediment yield, total nitrogen (TN), and total phosphorous (TP) at outlets of three sub-basins of the BSRW, and within the SSW. BMP scenarios of check-dam, tail water pond, vegetative filter strips (VFS), nutrient management, and tillage management were evaluated for their efficacy in reducing streamflow, sediment yield, and nutrient loads at field and watershed scales. The VFS was determined as the most effective BMP in decreasing sediment yield, TN, and TP at both field and watershed scales. At field scale, reduction of sediment yield, TN, and TP by VFS ranged from 8 to 12%, 71% to 98%, and 72% to 99% respectively and at watershed scale, reduction of sediment yield, TN, and TP by VFS ranged from 12 to 38%, 29% to 87%, and 42% to 99% respectively. The application of conservation and zero tillage operation showed reduction in sediment yield by 1% to 2% respectively but increased TN and TP by 2% to 25% at field and watershed scale watersheds. This study will help in managing water at field and watershed scale watersheds regarding BMPs selection and implementation. Graphical Abstract

Evapotranspiration (ET) provides important information for hydrological studies, including estimating plant water requirements which can be derived from remote sensing data or simulated using hydrological models. In this study, ET derived from the Moderate Resolution Imaging Spectrometer (MODIS) was compared with ET simulated by the calibrated and validated Soil and Water Assessment Tool (SWAT) model for the Big Sunflower River watershed (BSRW) in Mississippi. The comparisons were made based on 8-day, 1-month, seasonal, and annual timescales. The coefficients of variation (COVs) for the 8-day, 1-month, seasonal, and annual ET simulated by SWAT were 0.42, 0.40, 0.32, and 0.04, respectively, whereas the COVs for the ET derived from MODIS were 0.06, 0.12, 0.08, and 0.01 for the respective time scales. Lower COVs for the ET derived from MODIS indicated lower sensitivity to crop growth in the field. SWAT-simulated ET was the highest during crop growing season and lowest during dormant season, but MODIS-derived ET did not vary considerably according to crop growing or harvesting seasons. As MODIS-derived ET accounts for only climatic conditions and vegetation cover, SWAT-simulated ET is recommended for the short-term estimation of crop water requirements because it accounts for climatic, land use, soil, and slope conditions.