Evaluation of the impact of climate and land use / land cover change on hydrological response in Gelna watershed

Abstract

Global climate change seriously impacts hydrological regimes, substantially impacting water resources and national food security. This study aimed to analyze the effect of climate and land use land cover (LULC) changes on catchment hydrological response for the Gelana River in Ethiopia. LULC images were developed through a supervised classification technique using the ERDAS platform, ArcGIS, and the cellular Automata-Markov model. The study highlighted significant land-use changes, with increased agriculture and built-up areas at the expense of forests and pasturelands. Coordinated regional downscaling experiment (CORDEX-AFRICA) datasets showed a decrease in rainfall (48.64% to 4.6%) and rising temperatures (minimum: 0.58–3.35˚C, maximum: 0.5–2.93˚C) under RCP 4.5 and 8.5 scenarios. Model calibration and validation were completed using monthly observed streamflow for the most sensitive parameters in the SWAT (Soil and Water Assessment Tool) Calibration of Uncertainty Program. The model performed well between actual and simulated streamflow, with R2, NSE, and PBIAS values of 0.84, 0.77, and -15.9 for calibration and 0.88, 0.8, and -14 for validation, respectively. Land-use changes resulted in reduced groundwater (0.81 to 0.7%) and potential evapotranspiration (61.5 to 54.4%), with moderate increases in surface runoff (6.39 to 9.4%), evaporation (23.19 to 27.2%), annual streamflow (3.22% to 23.82%), and water yield (8.1 to 11.7%). Climate change impacts showed higher potential evapotranspiration (23.49 to 29.13%), evaporation (23.69 to 27.35%), surface runoff (10.32 to 15.57%), and water yield (18.62 to 27.67%), but lower groundwater (24.49 to 20.87%) and annual streamflow (38.2% to 23.27%). The combined simulation showed the most significant hydrological shifts, including increased evaporation (2.79 to 17.79%), surface runoff (2.33 to 43.31%), and streamflow, water yield, and groundwater variability. Combined simulations reveal significant changes in water availability, posing long-term challenges for agriculture. Effective land-use planning and climate-resilient water management practices will be vital to risk management.