STREAM FLOW AND WATER AVAILABILITY FOR CROP PRODUCTION UNDER CLIMATE CHANGE SCENARIO; CASE STUDY OF WOYBO CATCHMENT, ETHIOPIA

Abstract

Climate change has a significant impact on water availability and agriculture water demand due to high evapotranspiration. This study aimed to evaluate the future surface water availability under the RCP scenario for crop production in the Woybo catchment. Six climate models were obtained from CORDEX Africa under the RCP4.5 and 8.5 scenarios, and the projection analysis was done from 2041–2070 and the 2071-2100 period. After evaluating its performance through statistical indices, the rainfall-runoff HEC-HMS model was used to simulate future stream flow. The CROPWAT 8.0 model was also used to determine the current and future crop water demand. The model revealed that it acceptably reproduced the volume and pattern of the observed hydrograph with a value of NSE = 0.66 & RVE = 1.57 for the calibration period and NSE = 0.56 & RVE = 9.75 for the validation period. The trend of selected climate variables was evaluated by Mann-Kendall’s tests and Sen’s slope estimators at a 5% significance level. Under the RCP4.5 and 8.5 scenarios, projections of both mid- and long-term annual rainfall showed decreasing and increasing trends, respectively. Under the RCP4.5 and 8.5 scenarios, the projections of both mid- and long-term annual rainfall showed decreasing and increasing trends. However, the potential evapotranspiration and maximum and minimum temperatures predict an increasing trend in all RCM models. The amount of annual stream flow will decrease by 17.29% to 4.87%, with a likely increase in annual potential evapotranspiration of 0.21–8.9% over the catchment. According to the result, the impact is season-dependent, with increased stream flow in the main rainy season but lower flow in the short rainy season and dry seasons. Future crop water requirements and irrigation water requirements are expected to increase for the maize crop due to increased rainfall and higher evapotranspiration in all climate models. This increased crop water demand and aggravated the soil moisture deficit in the catchment. The mid-growth stage had the highest incremental CWR and IWR, while the early and late stages had low CWR and IWR. Because the leaf area index (LAI) and plant height increased regularly from the initial to mid-season stages, increasing transpiration. As a result, this research contributes to increased crop yield and the development of adaptive strategies for the proper management of water resources