Jacques Lemoalle

A decision-support tool for water allocation in the Volta Basin

The first version of a decision-support tool (DST) for the management of the transboundary water resource of the Volta Basin is presented in this article. The DST coupled a hydrologic model with the Water Evaluation and Planning (WEAP) water‐allocation model. It was calibrated and validated by reproducing observed river flows and water stored in the hydropower reservoirs, respectively. It considered the impact of possible future climate changes (potentially critical) and the development of upstream small reservoirs (leading to upstream–downstream trade-offs) on the Akosombo hydropower scheme. This DST may foster transboundary dialogue for the integrated management of the basins water resources.

Cross-basin comparisons of water use, water scarcity and their impact on livelihoods: present and future.

We compare water availability, water use, water productivity and poverty across the diverse river basins studied by the CGIAR Challenge Program on Water and Food. Water productivity tends to be higher in drier areas and where livestock grazing is integrated with rainfed crop production. We find that links among water, food security and poverty are best understood within a historical perspective. We identify opportunities to reduce poverty through water-related interventions. The way in which water-related investments affect poverty is influenced by changes in demography, climate, and rural society. In most basins, these trends involve trade-offs that require good governance at local, regional and basin scales.

Farming systems and food production in the Volta Basin

The predominantly rural population in the Volta Basin depends on rainfed crops, a practice which becomes increasingly risky as the rainfall decreases from south to north and rural poverty increases. Yields are low throughout because of drought and dry spells within the growing season, infertile soils, low inputs, poor infrastructure, and low labour productivity. Water-related diseases are widespread and half of all rural households depend on low-quality water. Fertilizer and small-scale irrigation can improve the yields of rainfed crops and alleviate poverty, but the duality between the legal state and the traditional hierarchy complicates land tenure by hindering investment. Small-scale irrigation has little effect on hydropower dams downstream.

Modèle hydrologique du Lac Tchad

Résumé Le Lac Tchad est modélisé par un bilan de volume donnant ses niveaux et superficies de plans deau en fonction dapports et pertes: débit des tributaires; pluie; évaporation; infiltration. Il est représenté par trois réservoirs (cuvette nord et archipel connectés à la cuvette sud) dont les niveaux de plan deau, distincts en période dapports déficitaires (situation actuelle), sont confondus en période excédentaire (situation avant 1973). Suite aux observations de terrain, la cuvette nord est représentée avec un “réservoir sol” devant être rempli pour que leau puisse apparaître en surface. Le modèle utilise sept paramètres optimisés: intensité dinfiltration; profondeur du “réservoir sol”; quatre paramètres d’échange entre réservoirs; niveau de fond de larchipel. Grâce aux données mesurées au sol ou par satellite (débits, précipitations, évaporation, niveaux et superficie de plans deau) il est calé sur la période 1970–1996 et validé sur la période 1956–2008. Citation Bader, J.-C., Lemoalle, J. & Leblanc, M. (2011) Modèle hydrologique du Lac Tchad. Hydrol. Sci. J. 56(3), 411–425.

Yields and water productivity of rainfed grain crops in the Volta Basin, West Africa

The observed water productivity (WP, kilograms of crop per cubic metre of rain) of cereals is very low in the Volta Basin: mean WP barely reaches 0.15 kg/m3 for maize (±0.05), with a mean yield of 1.25 t/ha (±0.58). We sought to explain these observations by using simulation modelling to develop a frequency analysis along a 9° transect on the meridian of Ouagadougou, that is about the whole gradient of rainfall in the basin. At both plot and basin scale, the model indicated that fertilizers would allow much higher yields and thus better WP.

Lake Chad: A Changing Environment

In closed lakes, an equilibrium water level is reached when the surface area allows for an evaporation that balances the rain and stream flow into the lake. As these inflows are closely associated with rainfall over the basin, such water bodies are highly sensitive to the climate variability, and have been described as amplifier lakes. In natural conditions, they are good indicators of climate changes, but they also react rapidly to man-made changes in their water budget. An analysis of the hydrological and ecological functioning of some closed lakes experiencing modifications to their water budget may provide some pointers to future management strategies for water resources in endoreic basins subject to global climatic change. The recent evolution of Lake Chad is presented here in this context.