Evaluation of climate change Impact on stream flow of Mille watershed

Abstract

Climate change manifests itself primarily through changes in average temperature and precipitation, which affects in overall flow magnitude. This study evaluated the impact of climate change on stream flow of Mille watershed, which is situated in the North-East part of Ethiopia. Climate change is likely to affect the hydrology of the watershed. The study aims to assess the change of climate variables (precipitation and temperature) and stream flow of the study area. Different materials and methods were used to arrive at the stated objectives. Downscaled future climate projections of precipitation and temperature were developed from Hadley Global Environment Model 2-Earth System (HADGEM2- ES) under two radiative forcing scenarios (RCP4.5 and RCP8.5). These climate scenarios were bias corrected for each selected stations and areal rainfall over the catchment was determined. In this study, the period 1976-2005 was used as the baseline period, while 2041-2070 (2050’s) and 2071-2100 (2080’s) as the middle-future and the far-future respectively. As temperature projected the climate would become warmer for both scenarios in the future. The future projection of climate variable showed an increasing in minimum temperature by 1.4oC and 1.3oC for RCP4.5 and 1.5oC and 1.8oC for RCP8.5 in 2050’s and 2080’s respectively. As Rainfall projected the climate would become drier under RCP8.5, which showed a decrease in Rainfall by 8.05% and 8.73%, while under RCP4.5 Rainfall decrease by 3.87% in 2050’s but it become rise by 4.64% in 2080’s. The Soil and Water Assessment Tool (SWAT) model was calibrated and validated for stream flow simulation. The climate change variables used an input to SWAT model to simulate the future stream flow. The result showed a change in stream flow by -6.37% and 5.8% for RCP4.5, -13.9% and -26.3% for RCP8.5 in the period of 2050’s and 2080’s respectively. Results of this study are expected to arouse the serious concern about water resource availability in the Mille watershed under the continuously warming climate. Therefore, there is a need to minimize the sensitivity to climate change by making stringent climate polices