Abstract

Climate change and its impact on the basin's hydrological processes can progressively assist in addressing the difficulties that water resource managers and planners will face in the future. Estimating Crop Water Requirement (CWR) and irrigation water demand in a changing climate is critical for long-term water resource development and planning. Therefore, this study examines the climate change impact on the water balance of the Kankai river basin, Nepal. The study used the CMIP6 (Coupled Model Inter comparison Project) model output to project future climatic variables from 2015 to 2100, the SWAT (Soil and Water Analysis Tool) model to set up the rainfall-runoff model, SWAT CUP for calibration validation, sensitivity analysis, and future stream flow projection and CROPWAT8.0 (Crop Water and Irrigation Requirements Program) is used to estimate CWR and Irrigation Water Requirement (IWR). Ten general circulation models under two climate change scenarios (middle road approach i.e. ssp245, and high emission scenario i.e. ssp585) were considered to examine the impact of climate change on water balance. Results revealed that the effects of climate change are reflected in future river flow and irrigation water demand in the Kankai river basin. It shows that the maximum temperature rises from 0.72°C to 3.28°C, the minimum temperature rises from 0.91°C to 4.55°C and the precipitation varies from -7.43 % to +14.68 % in the middle road approach and high emission scenarios. According to the findings, the Kankai basin will likely increase rainfall and temperature in the future. The impact of increased rainfall and rise in temperature is reflected in yearly river flow, which is expected to increase by 11.65–36.74% compared to historical data from 1980 to 2014. Despite this rise, predictions show that the Kankai irrigation system will continue to be a water deficit basin in future decades from February to March.

Keywords: Agriculture; Climate change; SWAT; CMIP6; Kankai river basin; Irrigation water requirement; GCM