IMPACT OF CLIMATE CHANGE ON SOIL WATER AVAILABILITY AND MAIZE WATER NEEDS IN KESEM SUBBASIN, MIDDLE AWASH, ETHIOPIA

Abstract

synthetic systems. Accordingly, this study strives to quantify the climatic change impact of the study area, the likely change of rainfall and temperatures from the base period by near and mid future century using ensemble of CORDEX Africa RCM model output under two alternative scenarios, and the corresponding possible implications of those changes on soil water availability and crop water needs of Maize in Kesem subbasin, middle Awash, Ethiopia. Based on the result obtained from the bias corrected of future scenarios, the rainfall was projected to be increased by 2020s and 2050s for RCP4.5 and RCP8.5 scenarios. Concerning seasonal change, it was projected that Kiremt rain would likely to be increased by about 1.8% by 2020s and 20% by 2050s for RCP4.5 scenario and 6% by 2020s and 21.73% by 2050s for RCP8.5 scenario. The mean maximum temperature was predicted to be from +0.95 to 1.98oC by 2020s and 2050s for RCP4.5 and +1.38 to 2.83oC by 2020s and 2050s for RCP8.5 scenario respectively. Minimum temperature also predicted for the future period. Accordingly, it will be increased from 1.04 to 3.02oC by 2020s and 2050s for RCP4.5 scenario. In case of RCP8.5 scenario the corresponding increase of minimum temperature would be from 0.03 to 5.13oC by 2020s and 2050s. Beside climate change, land use/cover data were used as input of SWAT in baseline scenario with climate change on soil water availability and shows increasing trend in Agricultural land, bare land, settlement and decreasing in shrub and Acacia land in the sub basin. The LULC was simulated using CLUE-S model to project the land use changes under current baseline scenarios and revealed an increase in Agricultural land and decline in Acacia and shrub land. The calibrated SWAT model was used for nine years of baseline period and performed well for simulation of monthly stream flow. Statistical model performance measure, R2 of 0.84 and ENS of 0.78 for monthly calibration and R2 of 0.78 and ENS of 0.73 for monthly validation respectively, indicated well to very good performance of the model simulation. After an intensive model calibration and validation for sensitive flow parameters, comparison of monthly simulated soil water in baseline period shows increasing trend by about 3.6mm and decreasing by -0.95mm for 1984-1998 and 1999-2013 years respectively. Relative to base period, the soil water availability in the kiremt season reduced by 6.02% and 5.22% for RCP4.5 and 2.21% and 2.36% for RCP8.5 respectively for first and second fifteen years of 2020s. For reliable Maize production in terms of water demand, determination of onset, offset and LGP is crucial and assessed using INSTAT climate guide. Anchored in the bias corrected future climate scenarios, ETO and CWN were estimated. Overall, 0.04, 1.02% for RCP4.5 of 2020s and 2050s and 21.24, 24.29% change in ETO for RCP8.5 of 2020s and 2050s were predicted from base period. Crop water need have been predicted to increase by 8.16% and 10.39% for RCP4.5 and by 9.45% and 10.94% for RCP8.5 scenarios of 2020s and 2050s from the base period for the same level of production. The study investigate that due to combined effect of projected variation in rainfall and temperature and then affect soil water availability there will be increment of Maize water needs in Kesem subbasin.