Hydroclimatology of the Volta River Basin in West Africa: Trends and variability from 1901 to 2002

Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

“…These results concern four small basins located in a coastal area with a sub-equatorial regime (with two rainy seasons) covering 23,000 km 2 (the Bia, Tano, Ankobra and Pra Rivers basins; Figure 3), with annual rainfall amounts ranging from 1500 to 2000 mm. In the Volta River basin, downstream from the Akosombo dam featuring one of the largest reservoir in the world, Oguntunde et al [61] noticed that, between the 1931-1960 and the 1970-1998 periods, discharges of the Volta River decreased by 16%, for a 10% reduction of rainfall in the whole basin. This trend matches with the Great Drought, but also with the dam building, and the creation of the Volta Lake, which constitutes a big evaporation pan.…”

“…Damming significantly influenced the water balance of only the greater basins, such as the Volta [61], the Senegal [21,22] and the Niger. However, by comparing the dam-equipped basin of the Mono River (Benin) with the unequipped one of the Couffo River (in Togo), Amoussou et al [27] observed (in relatively small basins) an annual excess of stream flow in 37% of the Mono River after 1988 for a small increase in rainfall (+2%), while they did not observe any modification in the "natural" Couffo River basin.…”

“…Figure 5. Classification of rivers basins according to the five described types (Volta River was added, despite the biases introduced by Akosombo dam, in Type 1, as the literature well describes its behavior); Sokoto is type 2, since an increase in RC is observed, but data are very sparse [2,3,15,49,61,63,64,68,72]; Komadugu has the same behavior as the Sahelian Basin (personal communication with Pierre Genthon, IRD). Figure 5.…”

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“…The largest change was reported by 97 mm increase for the western USA in a warm season during past 45 years [57]. Likewise, increasing trends were reported in Israel [3], Brazil [4], eastern Asia [5], western Africa [6], and Iran [7]. In Turkey, [34] reported a decreasing trend while [35] reported both decreasing and increasing trends in different regions.…”

“…Increasing trends in evaporation were reported in Israel [3], Brazil [4], eastern Asia including Tibetan Plateau, China and Japan [5], western Africa [6] and Iran [7]. On the other hand, decreasing trends were also reported in the USA [8], the USA and former Soviet Union [9], Italy [10], Australia [11], Japan [12], China [13][14], Thailand [15][16], Canada [2], and India [1,17].…”