Anthropogenic and climate drivers of Blue and Green water dynamics in Uganda’s Aswa catchment

Effective water resources management is essential in regions experiencing land-use change and climate variability. This study investigated the spatiotemporal dynamics of Blue Water (BW) and Green Water (GW) in Uganda's Aswa 1 sub-catchment from 1990 to 2024 using the Soil and Water Assessment Tool Plus (SWAT+) and satellite-derived land use/land cover (LULC) data. Landsat imagery and NASA POWER climate data were used to assess land-use transitions, climate variability, and hydrological responses across seven sub-basins and 282 Hydrological Response Units (HRUs). Trends were analysed using the Mann–Kendall test and Sen's slope estimator. The SWAT+ model showed satisfactory performance, with calibration results of NSE = 0.76 and R² = 0.77 (PBIAS = −.63%) and validation results of NSE = 0.86 and R² = 0.86 (PBIAS = −.43%). Green Water remained relatively stable, whereas Blue Water was highly sensitive to precipitation and temperature variations. Agricultural expansion reduced soil water retention and increased surface runoff. Sub-basins 2 (Abim), 6 (Alebtong and Otuke), and 7 (Lira and Pader) were identified as hydrological hotspots due to significant changes in water yield and evapotranspiration sensitivity. The findings highlight the need for integrated watershed planning and climate-resilient water governance in climate-sensitive regions.