CLIMATE CHANGE IMPACT ASSESSMENT ON RUNOFF POTENTIAL IN UPPER AWASH BASIN: A CASE STUDY OF LEGEDADI - DIRE CATCHMENT

Abstract

Climate change is a global challenge. It is known regional hydrology is influenced by global climate change, through changes in patterns of precipitation temperature, runoff and other hydrologic variables. This has serious consequences on societal development and the costs of achieving adequate levels of water security. In this study climate change impacts on runoff water potential at catchment scale for the two selected catchment in Upper Awash Basin have been assessed. The two catchments included in the study were Legedadi (205 Km 2 ) and Dire (77.56 Km 2 ) catchments. A 0.44° resolution data of Coupled Model Inter-comparison Phase5 (CMIP5) global climate models (GCMs) output of precipitation and temperature (max& min) for 2020’s (2016-2035), 2050’s (2046-2065) and 2080’s (2081-2100) under (RCP 4.5) were applied to assess the climate change scenarios. Bias correction was applied to these forcing variables. Moreover, a hydrological model, Arc-SWAT, was utilized to simulate runoff in the study area. Sensitivity analysis result shown that Curve Number (CN) factor are the most sensitive parameters affecting the hydrology of the catchments. The model was calibrated from 1988-1997 and validated from 1998-2003 at the estimated outlet of Legedadi and Dire catchment. In terms of hydrological modeling performance, at both catchments (NSE) indices are greater than 0.8 and 0.85 for calibration and validation period respectively. Future projections results as compared to base period (1986-2005) have shown that, the annual precipitation exhibit an increasing trend. Maximum increment is observed for 2050s projection with +11.9% at Legedadi and 11.3% at Dire. The seasonal rainfall increment is more pronounced at 2050`s than 2020s and 2080s at both catchments, higher increment is observed on season (JJAS) at 2050s, decrement is on season FMAM at Legedadi and ONDJ at Dire it ranges (+18.5% & -13.1% at Legedadi) and (18.6% and -68.1% at Dire) at 2080s. The mean daily temperature increases for future periods (2020`s, 2050’s, and 2080`s) with maximum increment of +17.7% in 2080s. In general in both study catchments; the impact of climate change may cause an increase in annual runoff for future periods. It may rise up to 14.3% in Legedadi and 17% in Dire catchments in the 2050s.High Seasonal mean runoff may be observed at Kiremt season and high radiation may be observed on Bulge season. It ranges (+20%and -32% Legedadi) (+23.9% & -51.9% Dire). The sensitivity analysis has shown that both catchments are more sensitive to rainfall. The increase in runoff magnitude may probably have positive impacts in meeting the water supply demands to Addis Ababa city.