INVESTIGATION OF WATER RESOURCE AVAILABILITY AND IRRIGATION WATER DEMAND UNDER CLIMATE CHANGE IN DAWA RIVER BASIN, ETHIOPIA

Abstract

Climate change and its impact is the concerned issue that threatening the world wide especially east Africa including Ethiopia. Water resource availability is directly impacted by climate change, which is the outcome of change in climate variables like rainfall and temperature. Accordingly this study aimed to examine the response of water resource availability and irrigation water demand(IWD) to climate change in Dawa sub basin, Ethiopia, using ensemble of regional climate model (RCM) output from coordinated regional climate downscaling experiment (CORDEX) Africa under future medium and high climate change scenarios(RCP4.5 and RCP8.5).The bias corrected result showed that, the spatially averaged annual rainfall was projected to decline by - 17.95% and -19.66% under RCP 4.5 and RCP8.5 scenarios, respectively for the 2021-2050 time period. In the same way, the RCP4.5 and RCP8.5 scenarios, projected that the annual rainfall would decline by -12.9% and-22.4% respectively, in the time period 2051-2080. Mean annual maximum temperature was projected to increase by 1.6℃ and 2.3℃ under RCP4.5 and RCP8.5 of 2021-2050 and by 1.4℃ and 2.8℃ under RCP4.5 and RCP8.5 scenarios of 2051-2080 time interval. Accordingly the mean annual minimum temperature was projected to increase by1.6℃ and 3.5℃ under RCP4.5 and RCP8.5 scenarios of 2021-2050 and by 2.03℃ and 4.1℃ in 2051- 2080 under RCP4.5 and RCP8.5 scenarios respectively. To analysis water resource availability and irrigation water demand soil and water assessment tool (SWAT) and CROPWAT model were employed. SWAT was calibrated and validated on monthly base streamflow and performed well with statistical model performance measures of NSE=0.75 and R2=0.82 for calibration and NSE=0.71 and R2=0.77 for validation. In comparison to the baseline period, it is expected that the future annual streamflow will decline under RCP4.5 scenario by -31.3% to -52.9% and under RCP8.5 scenarios by -27.5 to -41.3%. CROPWAT estimate current and future irrigation water demand and results indicated that the averaged IWD would increase by 5.8% and 3% under RCP4.5 and by 12% and 9.2% under RCP8.5 scenarios. To sum up, this study looked into how the projected change in rainfall and temperature resulted in reduction of water resources availability and increment of irrigation water demand of maize in Dawa river basin. Thus sustainable and effective adaptive measures is crucial for future water resource management