Rainfall-Runoff Modeling Under Changing Climate and Land Use Land Cover: A Case of Mille River Watershed, Lower Awash Sub-Basin, Ethiopia

Abstract

The rainfall-runoff model is a crucial and necessary tool for water resources management. Both climate change and land use land cover (LULC) dynamics are critical factors influencing hydrological processes by altering groundwater recharge and river flow. This study investigates the impacts of land use/land cover (LULC) changes and climate change on rainfall-runoff processes in the Mille River Watershed, Ethiopia, using the SWAT hydrological model. Historical LULC changes (2000, 2010, and 2020) were analyzed using remote sensing data, while future LULC scenarios for 2030 and 2050 were projected using the CA-Markov model. Past trends revealed significant agricultural expansion and settlement growth, which increased mean annual flow by 1.26%, wet-season flow by 2.68%, but decreased dry-season flow by 2.22%. Future LULC changes are projected to cause a 1.19% increase in mean annual flow, with wet-season flow rising by 2.9% and dry-season flow declining by 3.14%. Climate projections, derived from the CanESM5 model under SSP2-4.5 and SSP5-8.5 scenarios, indicate increases in mean annual precipitation by up to 15% and mean annual maximum temperature by 1.05°C (SSP5-8.5) by 2050. These changes are expected to increase mean annual flow by 7.63% (SSP2-4.5) and 8.13% (SSP5-8.5) in the near term (2025–2055), with slightly greater increases in the mid-term (2056–2085). The combined effects of LULC and climate change show a more pronounced increase in streamflow compared to their individual impacts. However, climate change emerges as the dominant driver due to its widespread and persistent alterations in precipitation patterns and temperature regimes, which directly influence the hydrological cycle beyond localized land cover changes. SWAT model calibration and validation yielded reliable performance metrics, with NSE = 0.78 and R² = 0.82 during calibration and NSE = 0.75 and R² = 0.79 during validation. The results highlight the need for integrated watershed management strategies to mitigate the risks of increased streamflow, flooding, and water scarcity. Sustainable land management, afforestation, soil conservation measures, and adaptive climate strategies are essential for ensuring long-term water security and resilience in the Mille River Watershed.