Recent and future developments in the Volta River basin from a Nexus perspective: Synergies and trade-offs between different water uses under climate change

To feed the growing population, achieve the Sustainable Development Goals, and fulfil the commitments of the Paris Agreement, West African countries need to invest in agriculture and renewable energy, among other sectors. Irrigated agriculture, feeding millions of people, and hydropower, which generates clean electricity, both depend on the availability of water. We have investigated the extent to which synergies and trade-offs exist between simulated water demand and supply of three planned irrigation sites in the Volta basin and the hydropower potential at four dams using an eco-hydrological model. The impacts in terms of changes in the water balance and availability were attributed to single projects (irrigation site or dam).

We found that without upstream reservoirs, the naturally intermittent flow regime of the Black and White Volta Rivers either limits or makes dry-season irrigation impossible, depending on the location (climate) in the basin. The planned additional irrigated area of 104,000 ha could feed about half a million people but relies on upstream dams transforming the intermittent to a permanent flow regime. Irrigation withdrawals would be at the expense of hydropower potential, which decreased by 139 GWh/a. The 182 GWh/a of the planned Pwalugu dam thus contribute only 24% of its potential. Moreover, our process-based simulations revealed that solely the transformation from intermittent to permanent flow regime caused accumulating transmission losses downstream, which can be substantial.

Simulated future crop water requirements did not increase under climate change projections using an ensemble of 8 bias-adjusted global climate models, because the higher evaporative demand was outbalanced by increasing precipitation.