Application of the water accounting plus (WA+) framework for the assessment of water availability and consumption in the Zambezi River Basin (ZRB)

Abstract

Study region The Zambezi River Basin (ZRB) is a large transboundary basin in south-central Africa shared by eight countries. It provides vital water resources for hydropower, agriculture, ecosystems, and human use across the region. Study focus The remote sensing-based Water Accounting Plus (WA+) framework was applied to the ZRB from 2003 to 2023 to quantify its water balance. The WA + methodology was used to overcome sparse ground data by leveraging satellite-derived datasets such as precipitation ( P ), actual evapotranspiration ( ET a ) and land cover and use (LULC). New hydrological insights for the region The WA + water balance for the ZRB reveals that P (1280.5 km³/year) is the dominant inflow, while ET a (1095.6 km³/year) constitutes 85.5% of the gross inflow. This leaves a long-term mean surface water yield ( P–ET a ) of 184.9 km³ /year. A substantial portion of the inflow (115.9 km³/year) is lost to storage, suggesting significant basin-scale water-storage potential. The exploitable water averages 106.6 km³ /year, of which 19.9 km³ /year is reserved outflow and 0.2 km³ /year is non-utilisable outflow; thus, about 86.4 km³ /year remains available for use. Currently, 44.5 km³ /year is utilised flow, leaving 42.0 km³ /year that is still undeveloped. Overall, the basin sustains a net-positive water balance, though water availability declined over the study period, coinciding with a general downward tendency in P and elevated ET a in recent years; however, the basin-scale trends in P and ET a were not statistically significant.