Evaluation of loss models and effect of LULC changes on surface runoff in Subarnarekha River Basin in India

Precipitation is essential to understand rainfall-runoff phenomenon for estimation of water availability. The main focus of study is to compute the surface runoff and to assess the impact of Land Use Land Cover Changes (LULCC) with the help of hydrological model (ArcSWAT) in Subarnarekha River Basin (SRB) over a period of 1999-2014. For runoff simulation, two different loss models were considered: SCS-CN (Soil Conservation Services-Curve Number) model and Green-Ampt model (GA). Different maps like drainage map, elevation map, land use/land cover map, slope map and soil map of the watershed are prepared using remote sensing and GIS approaches as an input data to the model. Runoff has been simulated at six observing stations located at Adityapur, Jamshedpur, Ghatsila, Jamsholaghat, Fekoghat and Rajghat. During this period, runoff is found to increase by 6.06% due to decrease in infiltration rate.The comparison between the observed and estimated data shows the Nash-Sutcliffe efficiency (NSE) is 0.86 and 0.85 and Coefficient of determination (R2) values are 0.89 and 0.87 in SCS-CN and GA methods respectively. Thus SCS model was found to do well than GA model in Subarnarekha River Basin. Calibration and validation of the model were performed with soil and water assessment tool-calibration uncertainty programs (SWAT-CUPs) with sequential uncertainty fitting (SUFI-2) algorithm. The sensitivity analysis of basin parameters has been analyzed in order to improve the runoff simulation efficiency of the model. For monthly stream flows the NSE and R2 values were 0.86 and 0.88 during calibration period (2002-2009) and 0.88 and 0.89 during validation period (2010-2014) respectively. However, the number of days of high intensity rainfall has increased over decade which along with the land use changes explains for the increase in streamflow. The end result of this study could be useful in runoff simulation and flood forecasting for extreme rainfall events in Subarna rekha River basin and beneficiary for the watershed development.