MODELING THE IMPACT OF LAND USE/LAND COVER AND CLIMATE CHANGE ON THE HYDROLOGICAL BEHAVIOR OF ANDASA RIVER CATCHMENT BY USING SWAT

Abstract

Andasa River Catchment is one of the tributary of Abay River located in Upper Blue Nile Basin. In the catchment climate change and land use impacts were not well studied and quantified yet. Hydrological modeling of catchments is essential for future water resource development programs to provide information for decision makers and planners. For hydrological model Simulation SWAT model was used after calibrating and validating the sensitive parameters of the catchment. The calibration, validation and uncertainty estimation were done by SWAT-CUP in particular by SUFI2 project. The model has very good performances to use for the catchment and further, the model is capable to simulate climate change impacts and land use scenarios. Following SWAT model setup, future climate change scenarios were developed for the catchment and their subsequent impact on the water balance were estimated. This study used HadCM3 GCM model from fourth assessment report of the IPCC under A2 (high) and B2 (low) emission scenarios and CanESM2 model from fifth assessment report of the IPCC under RCP4.5 and 8.5 representing the maximum and minimum condition of CO2 emissions. The coarse GCM resolution was down-scaled by Statistical Downscaling Model (SDSM). The model used to downscale the station level weather variables temperature (minimum and maximum) and rain fall called predictand with the coarse GCM predictors by the principle of multiple regression for the future till 2099 /2100. The future downscaled weather variables were divided into 3 periods; 2013-2042, 2043-2072, and 2073-2099. The change in temperature (˚C) and rain fall (%) is calculated for the three periods in comparison to the base period (1993-2012). The climate projection result indicated increasing monthly temperature and decreasing tendency of rain fall under all scenarios. However, all scenarios agreed in increasing temperature and decreasing rain fall trends in the three periods while averaged. The change in temperature (˚C) and rain fall (%) is introduced to SWAT to simulate the water balances. Based on SWAT model simulation significant reduction of stream flow was observed under almost all scenarios in all future periods. Moreover land use scenarios were developed for the base period (1991-2012) and for future period (2013-2042). Best case scenario (afforestation and conservation) were developed for the two periods. Agricultural land expansions considered as worst case scenario. And their respective hydrological simulation indicated that in best case scenario significant increase in infiltration was observed. Hence, it enhances base flow and maintains stable dry season flow in comparison to worst case scenario