Thesis (M.Eng.) - Asian Institute of Technology, 2018

The requirements for the degree of Master of Engineeing in Water Engineering and Management

Future climate data for temperature and precipitation obtained from climate models were bias corrected using the linear scaling method. Maximum and minimum temperatures and precipitation were projected for three future periods: Near future (2018-2040),MF (2041-2070) and FF (2070-2099)against the baseline period of 1980-2005. The mean annual temperature in the basin is projected to increase by 1.1°C, 2.2°C and 3.2°C in near future, mid future and far futurerespectively. The mean annual precipitation is projected to increaseexcept in mid future under RCP4.5whereas monthly precipitation is expected to increase and decrease according to the months for the whole river basin, under RCP 4.5 and RCP 8.5scenarios, by 2100. Thecalibration of the spatially distributed hydrological models is complex due to the lack of reliable data, uncertainty in representing the physical features of a river catchment, and the implementation of hydrological processes in a simulation model. In this research, calibration of the Soil and Water Assessment Tool (SWAT) model is done by incorporation of remote sensing-MODIS AETand monthly discharge data at sub-basin.The calibration result showed good performance with Nash coefficientof 0.73during calibration period and 0.75during validation with AET. Similarly with monthly discharge in one of the sub-catchment Nashcoefficient is 0.75 for calibration period and 0.84 for validation period.Results show that the annual average precipitation, actual evapotranspiration (ET) and net water yields of the whole basin were 2,010millimeters (mm), 746mm and 1,219mm, respectivelyfor the baseline period. Due to the climate change, the result showed increase in net water yield, with slight decreasing trend in actual evapotranspiration. In addition, high flows in the basin are expected to increase which indicates that flood risk can increase whereas, increase in low flow can be taken as opportunity. So, the ministries and departments should consider the impact accordingly. From the Aqua crop model, it was estimated that cereal yield (rice, wheat and maize) were increasing for all future period. Adaptation strategies {u2013}such as increasing FYM application, and other management practices that will improve soil fertility will be important in enhancement ofcrop production and taking advantage of beneficial changes in climate.