Programme OS1k IWRM and water
Water allocation and climate change in a West African transboundary
Author(s): Devaraj de Condappa, Anne Chaponnière, Jacques Lemoalle, I. Terrasson, I. Asamoah, B.
Session: OS1k IWRM and water
Most of the Volta basin (83 % of
a total of 417000 km2) lies in Ghana and Burkina Faso, while Benin, Togo, Côte-d’Ivoire and Mali share the
remaining 17 %. Although the part of Togo is a small fraction of the basin (6.4 %), it covers a significant part of the
country itself (47 %).
To the contrary to most river basins, the upper part of the basin lies in semi-arid areas and
the rivers, more of them being seasonal, flow toward the more humid lower basin and the Guinean Gulf. There is thus
a tendency to develop water conservation, with numerous small dams and some medium size reservoirs in the upper
basin, while the Akosombo/Kpong hydroelectric compound, with Lake Volta, the biggest reservoir in Africa, lies in
the lower part of the basin, only 90 km from the ocean. If hydropower is high priority on Ghana’s agenda, it’s not on
Burkina’s agenda. These different uses of water in different parts of the basin set the scene for the need of some
concertation for water allocation in a context of climate change and increasing population at a rate of 2.5 to 3 % per
year. Concerns are rising on the ability of the resources to face the demands which are sometimes competing
between riparian countries but also among countries themselves.
A hydrological model of the surface hydrology of
the Volta basin has been developed to feed a water allocation model (the Water Evaluation And Planning system,
developed by the Stockholm Environment Institute). The scenarios for 2025 and 2050 include climatic and socio-
economic variables. The rainfall scenarios consider three hypotheses: no change relative to present, a decrease of
180 mm/y and an increase of 180 mm/y. The latter increase would broadly correspond to the pre 1970 rainfall in the
basin. In the socioeconomic scenarios, we have included the development of formal and small scale irrigation (a 30%
increase in 2050), and of total basin population from the present 17.2 million to 63 million in 2050, with a sharp
increase in the urban/rural ratio.
In this paper we are first presenting the Volta basin: water supplies (rivers,
aquifers, reservoirs, dams), and demand sites. The implementation of WEAP for the basin is illustrated along with the
assumptions made and the outputs of the model for the current situation are discussed. A second part presents the
population growth and climate change scenarios selected and implemented together with their simulated impacts on
the basin water resources situation. The last part is discussing these results and the way forward.