Combining Water Accounting Plus (WA+) and Hydrological Modelling for Water Resource Reporting under Climate Change in the Volta Basin

Informed water management critically relies on timely quantified and reliable information, which allows decision makers to design and implement sound policies to cope with water scarcity and sustain water security. Water accounting frameworks are useful tools for reporting on water resources availability and uses. Here, we combine the Water Accounting Plus (WA+) framework with hydrological modelling and climate change scenarios to quantify current and future conditions of water resources in the Volta River basin located in West Africa. Hydrological processes derived from the fully distributed mesoscale Hydrologic Model (mHM) are fed into the WA+ framework to provide a comprehensive report on the current state and future trends of water resources. mHM is used to predict water fluxes, stocks and flows for the historical period 1999-2020 and the near future (2021-2050). Climate change projection datasets are obtained from a large ensemble of nine global climate models (GCMs) and four regional climate models (RCMs) under the emission scenario RCP8.5. The WA+ report shows that the long-term net inflow in the basin over the period 1991-2020 is 389 km3/year and is projected to increase by 5% in the near future. However, only 8% of the net inflow is exploitable as “blue water”, while the remainder is consumed as “green water”, mainly in non-managed lands. The available water for various water uses in the basin amounts to 15 km3/year, of which 79% is utilized, while the remainder 21% is utilizable but not consumed. Only 42% of water use is beneficial for the intended purposes, with agriculture responsible for 35% of the beneficial water consumption. Future projections show an increase of 20% in the exploitable water fraction, while the available water fraction is expected to decrease by 5%. These findings show that climate change could disproportionally affect the exploitable and the available water, thereby calling for adaptation measures by the local authorities in the Volta River basin.