IMPACT OF CLIMATE AND LAND USE LAND COVER CHANGE ON STREAMFLOW: A CASE STUDY OF YADOT RIVER WATERSHED, GENALE DAWA BASIN, ETHIOPIA

Abstract

Both climate and land use land cover (LULC) change are the main factors that influence hydrological regimes by altering the magnitude of ground water recharge and river flow. Thus, for predicting future stream flow both climate and LULC changes projection should be accounted. In this study, Cellular Automata (CA)-Markov in IDRISI software was used to predict the future LULC scenarios and the ensemble mean of three regional climate models (RCMs) in the coordinated regional climate downscaling experiment (CORDEX)-RCM daily precipitation and temperature for Ethiopia under RCP 4.5 (medium emission scenarios) and RCP 8.5(higher emission scenarios) were used for the future climate scenarios. Power transformation and variance scaling method were used to correct bias the RCMs outputs, with respect to the observed precipitation and temperature. The separate and combined impact of climate and LULC change on stream flow was analyzed using SWAT hydrological model. The calibrated and validated for stream flow simulation using SWAT-CUP with a method of SUFI2.The performance of the model was assessed through calibration and validation process and resulted R2 = 0.8 and ENS = 0.73 during calibration and R2 = 0.83 and ENS = 0.77 during validation on monthly base simulation. The results of the ensemble mean of the three RCMs (CCLM4.8, RACMO22T and EC-EARTH) output show parallel precipitation and temperature increasing trends in the future under RCP4.5 and RCP8.5 scenarios but vary on monthly basis. The increases in mean annual maximum and minimum temperatures are higher for higher emission scenarios than medium emission scenarios. The LULC results showed that both in the past and future period, agricultural and settlement are significantly increased while forest land and scrub/bush lands continuously declined conversely grass/range lands and wood land show decline in the past and increased from 2015 to 2035 and again decreased from 2035 to 2055 in the future period. The past LULC caused an increased mean annual flow by 1.26%, and wet season flow by 2.68% but dry season flow decreased by 2.22% while the future LULC 2015 to 2055 will cause mean annual flow increased by 1.19%, and wet season flow by 2.9% but by decreased for dry season flow by 3.14%. The mean annual flow is projected to increase under both climate and combined scenarios by 7.63% (8.13%) and 5.76% (6.26%) in the near (2021-2050), while in the midterm (2051 – 2080) flow increased by 5.76% (6.26) and 6.07% (6.72%) at the outlet of the watershed under RCP4.5 and RCP8.5 scenarios, respectively. Generally, results of future stream flow projection indicated that the combined change of climate and LULC have relatively higher than the climate changed alone. Such studies enhance better understanding of the various impacts of climate and LULC change scenarios on stream flow, which can be used for better adaptation and mitigation of water resources management problem in the watershed by Appling different water and soil conservation measures.