Programme  OS1k IWRM and water allocation  abstract 238

Water allocation and climate change in a West African transboundary basin (Volta)

Author(s): Devaraj de Condappa, Anne Chaponnière, Jacques Lemoalle, I. Terrasson, I. Asamoah, B. Boubacar


Article: abs238_article.pdf
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Session: OS1k IWRM and water allocation
AbstractMost 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.

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