Evaluating the impacts of land use/land cover change on soil moisture dynamics for sustainable water resources management in the Gojeb River sub-basin

Abstract

Land Use/Land Cover (LULC) change is a fundamental driver of hydrological process changes, yet its immediate impact on soil moisture dynamics in tropical highland basins remains uncertain. Building on previous research that documented striking LULC changes in the Gojeb River sub-basin between 2000 and 2024, this study investigated the consequent impacts on the spatiotemporal dynamics of surface soil moisture. Using a 2000, 2011, and 2024 time series of Landsat imagery, the Normalized Difference Moisture Index (NDMI) was applied as a suitable proxy for soil surface water and vegetation water content. The study revealed an extreme anthropogenic modification of the soil moisture regimes of the basin with a decline in its peak NDMI values by 35.5% and significant contraction of its dynamic hydrological range. These trends indicate a drastic reduction in the water retention capacity of the landscape and an eroding ecological resilience. The strong correlation between Normalized Difference Moisture Index (NDVI) and NDMI indicated that 83% to 89% of the variance in vegetation water content is explained by the variance in vegetation greenness and health, justifying NDVI as a reliable indicator of NDMI in the study area. Spatially, the most significant losses in moisture were closely associated with areas where natural vegetation and wetlands were converted into agricultural fields and settlements. The degradation of these natural ecosystems, which are key hydrological regulators, has reduced the water retention capacity of the soil in the basin. This depletion of soil moisture has serious consequences on agricultural productivity, groundwater recharge, and base flow sustainability, besides increasing surface runoff and erosion. These ultimately threaten the long-term function of the downstream Gibe III hydropower reservoir through increased sedimentation. The findings urge prompt soil moisture-sensitive land use planning and conservation strategies to contribute towards water security and improved sustainable watershed management in the region.