Land use and land cover (LULC) change is a major driver of hydrological alteration in tropical river basins, with significant implications for water resources sustainability. This study assessed the influence of historical (1991-2021) and projected (2021-2041) LULC dynamics on the hydrological response of the Kilombero River Catchment (KRC) using the Soil and Water Assessment Tool (SWAT). The model was calibrated and validated against observed streamflow at the Swero (1KB17) gauging station, demonstrating satisfactory and moderate performance, respectively. Results indicated that expansion of cultivated land and grassland at the expense of forests, woodlands, and wetlands has increased surface runoff and sediment yield while reducing groundwater recharge and dry season flows. Between 1991 and 2021, surface runoff increased by approximately 14%, accompanied by a decline in groundwater contribution to streamflow of more than 8%. Future LULC scenarios project further amplification of these trends, with dry season flows falling below recommended e-flow requirements. The findings highlight that unmanaged LULC transformation is progressively weakening hydrological regulation and flow resilience in KRC. Integrating land use planning, ecosystem conservation, and environmental flow considerations into basin-scale water resources management is therefore essential to safeguard long-term hydrological and ecological sustainability.
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