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Abstract

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 agricultural
development and renewable energy, among other sectors. Irrigated agriculture, feeding millions of
people, and hydropower, generating clean electricity, depend on water availability and compete for
the resource. In the Volta basin, the planned 105 000 ha of irrigated land in Burkina Faso and
Ghana could feed hundreds of thousands of people. However, irrigation in the dry season depends
on upstream dams that change the river’s flow regime from intermittent to permanent, and at the
same time irrigation water is no longer available for hydropower generation. Using an integrated
eco-hydrological and water management model, we investigated the water demand and supply of
three planned irrigation projects and the impacts of the planned Pwalugu multi-purpose dam on
the hydropower potentials and water availability in the entire Volta basin. We found that future
irrigation withdrawals would reduce the hydropower potential in the Volta basin by 79 GWh a−1
and the operation of Pwalugu by another 86 GWh a−1. Hence, Pwalugu contributes only about 101
GWh a−1 of its potential of 187 GWh a−1. Under climate change simulations, using an ensemble of
eight bias-adjusted and downscaled GCMs, irrigation demand surprisingly did not increase. The
higher evaporation losses due to higher temperatures were compensated by increasing
precipitation while favouring hydropower generation. However, water availability at the irrigation
site in Burkina Faso is clearly at its limit, while capacity in Ghana is not yet exhausted. Due to
hydro-climatic differences in the Volta basin, the cost of irrigating one hectare of land in terms of
lost hydropower potential follows a north-south gradient from the hot and dry north to the humid
south. Nevertheless, food production should have priority over hydropower, which can be
compensated by other renewables energies.