Scenario-based analysis of upstream land use Land Cover Changes (LULC) in the Densu River Basin (DRB) on catchment hydrology including the Weija Reservoir, Ghana

Study region: Densu River Basin (DRB) in Ghana. Study focus: Urbanization, agricultural expansion, and population growth are transforming land use across West Africa, impacting hydrological regimes and ecosystem resilience. This study assesses land use and land cover (LULC) changes in Ghana’s Densu River Basin (DRB) using the Soil and Water Assessment Tool (SWAT). The model, calibrated (2012–2019) and validated (1990–2011) with streamflow data, showed strong performance (NSE = 0.79; R² = 0.85). Three LULC scenarios – agriculture-, forest-, and urban-dominated – were simulated using satellite imagery from 1990 to 2019. The 2018 Landsat baseline map, validated with 91.5% accuracy, showed the urban scenario increased surface runoff (>50% of water yield) and sediment load (>83,000 metric tons/year), while the forest scenario enhanced percolation and groundwater recharge. Sedimentation in the Weija Reservoir, a key water source for Greater Accra, deposits ∼47,500 m³ annually, posing long-term risks to reservoir capacity and water security. These findings highlight tropical catchment's vulnerability to land use changes and support scenario-based hydrological modelling for river basin planning in rapidly urbanizing, data-scarce sub-Saharan Africa.

研究区域：加纳登苏河流域（Densu River Basin, DRB）。研究重点：西非地区的城市化、农业扩张与人口增长正在重塑土地利用格局，对水文节律与生态系统韧性造成显著影响。本研究借助土壤与水评估工具（Soil and Water Assessment Tool, SWAT），对加纳登苏河流域的土地利用/土地覆被（Land Use and Land Cover, LULC）变化开展评估。该模型以径流量数据进行率定（2012–2019年）与验证（1990–2011年），模拟性能优异（纳什效率系数NSE=0.79；决定系数R²=0.85）。研究基于1990至2019年的卫星影像，模拟了农业主导、森林主导与城市主导三类土地利用覆被情景。经91.5%精度验证的2018年Landsat基准影像分析结果显示：城市主导情景下地表径流占产水量比例超50%，年泥沙负荷增量超83000公吨；而森林主导情景则提升了土壤渗透量与地下水补给量。作为大阿克拉地区关键水源的韦贾水库（Weija Reservoir），年泥沙淤积量约47500立方米，对水库库容与水安全构成长期威胁。本研究结果凸显了热带流域对土地利用变化的脆弱性，同时可为快速城市化、数据匮乏的撒哈拉以南非洲地区的流域规划提供基于情景的水文建模支撑。