Impact of regional climate change on water availability in the Volta basin of West Africa
The impact of climate change on the temporal and spatial distribution of precipitation, temperature, evapotranspiration and surface runoff in the Volta Basin (400 000 km2) of West Africa is investigated. Trend analysis shows clear positive trends with high levels of significance for temperature time series. Precipitation time series show both positive and negative trends, although most significant trends are negative. In the case of river discharge, a small number of (mostly positive) significant trends for the wet season are observed. High resolution regional climate simulation using explicit dynamic downscaling of the IS92a ECHAM4 global climate scenario indicates a slight increase in total annual precipitation of 5%, but also a significant decrease (up to 70%) of precipitation in April, which marks the transition from the dry season to the rainy season. The total duration of the rainy season is shortened. The simulated dry season temperature increase is around 1°C, while in the rainy season an increase of up to 2°C is projected. Expected temperature increase is smallest in the coastal areas and increases towards the north of the basin. An increase in mean annual surface runoff by 18% is anticipated. Predicted changes in precipitation, temperature, evapotranspiration and surface runoff show strong regional differences.