Modeling Rainfall-Runoff Relationship and Effects of Land Use Land Cover Dynamics on Hydrological Process in Mille Watershed, Lower Awash Basin, Ethiopia

Water resources are vital renewable resources that are the basis for the existence and development of a society. The response of hydrologic circulation is closely related to land use planning and management. Natural resource degradation resulting from inappropriate land use and subsequent hydrological change is one of the key problems threatening environmental welfare and sustainable development. The main objective of this study was to model the rainfall-runoff relationship and assess the effects of land use land cover (LULC) dynamics on hydrological processes in the Lower Awash Basin, Ethiopia using the Geographic and Information System (GIS) Soil and Water Assessment Tool (SWAT) model. GIS was used to generate land use and cover maps from Landsat TM and Sentinel-2 acquired, respectively, in 2000, 2010, and 2020. The land cover maps were generated using the Maximum Likelihood Algorithm of Supervised Classification. The accuracy of the classified maps was assessed using Confusion Metrics and Kappa Coefficient. The result of this analysis showed that, over two decades, cropland increased from 26.73% to 33.74%, while shrubland and forest declined from 30.56% to 22.70% and 2.72% to 1.35%, respectively, due to agricultural expansion and deforestation. They achieved overall accuracies of 85.56% (2000), 87.53% (2010), and 88.82% (2020), meeting the minimum reliability threshold of 85% for LULC mapping. Fifteen flow parameters were identified to be sensitive to the stream flow of the study area and used for model calibration. The SWAT model was calibrated and validated using monthly observed stream flow data for the baseline year (2000) and performed well (NSE ≥ 0.77 and R² greater than 0.73). An overall increase in the amount of surface runoff and actual evapotranspiration of 9.87% and 0.14% were observed in 2020 compared with the baseline year (2000). We conclude that the observed increase in surface runoff driven by LULC changes has significant impacts on environmental sustainability and water resource development. It is recommended to develop an appropriate land use planning and management strategy, along with implementing sustainable water resources management (WRM) techniques, to effectively address the challenges in the affected areas<br>