Assessment of groundwater recharge variability in the Usangu Plains under projected climate scenarios (2021–2050) for RCP 4.5 and RCP 8.5

ABSTRACT In the Usangu Plains of Tanzania, groundwater plays a crucial role in maintaining surface water as well as meeting domestic and agricultural water needs. This study aims to evaluate the influence of future climate projections on the water budget components, namely surface runoff (SR), actual evapotranspiration (AET), and groundwater recharge, using the WetSpass model. Under RCP 4.5, recharge varied from −205.66 to 7.6 × 10−6 mm, 0 to 2973.96 mm, and 0 to 2,968.91mm during the dry, wet seasons and annually, respectively. Under RCP 8.5, recharge ranged from −205.66 to 6.25 mm, 0 to 2,985.18 mm, and 0 to 2,988.49 mm in dry, wet periods and annually, respectively. Recharge is expected to be low in central region, high in southern and some southwestern regions, and moderate elsewhere. Results indicate high SR and AET, while recharge declines in magnitude and spatial distribution. The recharge decline will affect surface water within the area due to hydrological interconnections, leading to reduced water availability for agricultural, domestic, and economic needs. Therefore, proactive engagement from water users and stakeholders is essential for ensuring sustainable water planning and management. Strategies to minimize SR and AET are recommended to enhance both focused and diffuse recharge across the Usangu Plains.