Vol. 34, No. 7, 2016 2245 Estimation of Runoff for Aji basinusing SWAT model based on SCS-CN method National Academy of Agricultural Science (NAAS) Rating : 3. 03 © Serials Publications Estimation of Runoff for Aji basinusing SWAT model based on SCS-CN method Vithlani N. S.* 1 , Rank H.D. 2 and Prajapati G.V. 3 Abstract: Runoff is a very important factor in hydrological cycle and it is relevant for the watershed management programme for conservation and development or natural resources and its management. And Water resource planning and management is important and critical issue in arid and semi-arid regions.And availability of accurate information on runoff is very rare. Here three different bias corrected data scenarios are there (1961-2000), (2046-2064) and (2081- 2100). Soil and Water Assessment Tool (SWAT) is a physical based model developed for predict the runoff, erosion, sediment and nutrient transport from the watershed Runoff from a watershed affected by several geo-morphological parameters and for a particular watershed land use change can affect the runoff volume and runoff rate significantly. Here bias corrected data applied in SWAT model and SCS-CN method. Present study was undertaken to estimate surface runoff in the Aji basin situated in Rajkot, Gujarat, India using SWAT model and SCS-CN method. The Weight curve number for the Aji basin is 72.00. The coefficient of determination (R 2 ) for the daily and monthly runoff was obtained according to the SCS-CN and SWAT model are 0.852 and 0.947 respectively during 1961-2000. 0.88 and 0.964 respectively for the 2046-2064.Similarly 0.98 and 0.95 respectively for the 2081-2100.In this study found that SCS-curve number method along with SWAT MODEL can be used successfully in semi-arid region to simulate rainfall runoff and to estimate total surface water. Keywords:Hydrological modeling, Bias correction, Arc GIS, SWAT model, Runoff estimation, Curve number. 1 Research Associate, Centre of Excellence on Soil & Water Management, RTTC, Junagadh Agricultural University, Email: vithlaninipa@gmail.com 2 Head of Department of Soil and Water Engineering, College of Agricultural Engineering and Technology, Junagadh Agricultural University, 3 Assistance Research Scientist, Centre of Excellence on Soil & Water Management, RTTC, Junagadh Agricultural University, Junagadh, Email: prajapti_girish@jau.in INTRODUCTION Water is a transparent fluid which forms the streams, lakes, ocean and rain and is one of the major constituents of the fluids of living beings. Hydrological research deals with the distribution and circulation of water with environment. Agricultural systems in India need improved management strategies to increase their level of self- sufficiency in terms of food production. An increase in food production can only come from four sources such as capturing local rain, horizontal expansion of agriculture, food imports, or lower calories diets [9] . The SWAT is a semi-physically distributed hydrological model, operated on daily time step to simulate runoff and sediment at watershed scale [1, 2, 6] . The Soil and Assessment tool (SWAT) with Arc GIS interface can used for estimating the surface runoff. Different studies have shown that climate change significantly affects the hydrologic cycle and alters runoff regimes and water availability in different regions across the nation.The term ‘bias correction’ describes the process of re-scaling climate model output to reduce the effects of systematic errors in the climate models [10] . Future climate