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

Abstract

In this study climate change impacts on surface 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 by 0.44 degree resolution data of Coupled Model Inter-comparison Phase5 (CMIP5) global climate models (GCMs) output of precipitation and temperature (maximum and minimum) for 2020‟s (2016-2035), 2050‟s (2046-2065) and 2080‟s (2081-2100) under mid-range Representative Concentration Pathway (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 catchment s. 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 Nash-Sutcliffe (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% for Legedadi and 11.3% for Dire. For the coming 90 years, the mean monthly precipitation may both increase and decrease, high decrement may observe during (October to January ) months and, the increment may observe on (June to September) months. Legedadi has a range between (- 27% and +25%), Where as Dire‟s range is between (-63% and +32%). The mean daily temperature increases for future periods (2020`s, 2050‟s, and 2080`s) with maximum increment of +17% 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% in Legedadi and 17% in Dire catchments in the 2050s. Average monthly runo ff increases during Kermit months (wet month) and decrease in Bega months (dry month), ranging in between (+28% and -33%) in Legedadi and (+29% and -78%) in Dire catchments. High Seasonal mean flow may be observed at Kiremt season and high radiation may be observed on Bega season. 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.