Investigating the Impacts of Future Climate and Land use/Land cover Change on River Discharge in the Manafwa River Basin

Abstract

Land use/land cover (LULC) and climate are the most crucial drivers that shape the hydrological cycle, influencing infiltration, evapotranspiration, runoff generation, and groundwater recharge. While previous studies have provided valuable literature about the impacts of these drivers on river discharge, most assessments remain limited to historical and present conditions, leaving the future impacts of climate and LULC underexplored. Consequently, the lack of understanding of future river discharge behaviour hinders informed decision-making in water resource management and disaster preparedness. Guided by the main objective of investigating the impacts of future climate and land use/land cover on river discharge, this study applied the Soil and Water Assessment Tool (SWAT), which integrates historical analysis and future scenario assessment. Specifically, the study sought to determine LULC change in the Manafwa River Basin from 2000 to 2040 and to examine how projected climate and LULC conditions influence river discharge under different future scenarios. Historical LULC maps for 2000, 2010, and 2020 were generated using Random Forest classifier and projected to 2030 and 2040 using TerrSet’s Land Change Modeler based on historical LULC maps and drivers of change. Climate data was obtained from the NEX-GDDP-CMIP6 dataset and three Global Circulation Models (GCMs) were used to create an ensemble of three models, from which past and future climate were obtained. The SWAT model was then parameterized/calibrated and validated with observed stream flow data. Thereafter, scenario simulations were carried out using the separation method. Results indicate that LULC changes alone substantially modify basin hydrology, with mean discharge projected to increase by 4.49% (from 12.70 m³/s to 13.275 m³/s) between 2000 and 2040, alongside rising peak flows and reduced minimum flows due to vegetation loss and agricultural expansion. However, climate change scenarios greatly amplify hydrological extremes, with mean discharge projected to 14.01 m³/s (10.31%) by 2030 and 14.45 m³/s (13.78%) by 2040 under high emission pathways SSP2 and SSP5 respectively, peak flows were exceeding 20 m³/s, and minimum flows increasing to 6.507 m³/s. These findings indicate that, while climate change emerges as the dominant driver of future river discharge variability, LULC