Investigation of Total Nitrate Budget over a Sub Watershed in South India using Model Remote Sensing and Observational Data

Abstract

Global nitrate contamination in water, largely driven by human activities, poses a significant hazard. The Soil and Water Assessment Tool (SWAT) was used in this study to predict the nitrate concentrations in the Palar basin. Incorporating nitrate leaching dynamics, land use conditions, and conducting nitrogen budget estimation to identify sources and nitrate fluxes related to land use practices for establishing the nitrate-nitrogen budget. newlineThe study area is a poorly gauged river basin covering 17,818 km2, with a tropical climate, a slope of 0° to 60°, a dendritic and rectangular drainage network, an average annual rainfall of 875 mm, nine reservoirs, and numerous check dams. It receives moderate rainfall from the south-west monsoon and significant precipitation from the northeast monsoon. newlineThe evaluation of open-source products with SWAT simulated output carried out for surface runoff, water yield, evapotranspiration (ET), and potential evapotranspiration (PET) in the Palar River watershed, which includes a comparisons between the SWAT simulated runoff for the basin with the FLDAS and TerraClimate global runoff data. Additionally, comparisons were made between FLDAS Global model ET data with MODIS SSEBop and TerraClimate ET data with modelled SWAT ET data. The study also compared ERA5 reanalysis Hargreaves PET data with TerraClimate PET data and MERRA2 PET data with SWAT simulated PET data. Analysis of time series, seasonal, and yearly patterns from 2003 2021 revealed the highest monthly water yield observed during November December, with the peak annual yield at a maximum of 220 mm in 2010 and an average of 99 mm, which can be used to understand water resources for irrigation, drinking aspects, and net storage. The FLDAS and SWAT newlineix newlinesimulated surface runoff showed a resemblance in pattern and magnitude for the monthly and yearly time series of the average basin scenario. The monthly PET obtained from SWAT and ERA-5 showed a similar pattern for the entire basin and at the calibration site.