Total annual gross water loss through evaporation from hydropower reservoirs

Dam-induced impoundment of water in hydropower reservoirs usually causes enlarged water surfaces compared to the waterbody extent prior to dam construction (with the exception of reservoirs constrained by geomorphologic features, i.e. canyons). The annual gross water loss from reservoirs is determined by the reservoir surface area, annual evaporation and a shared use allocation factor in the case of multi-purpose reservoirs. Consequently, an enlarged reservoir surface area leads to a significant increase of water losses, depending on location’s climate regime and shared uses of reservoir water. This map shows the country-aggregated yearly gross water loss (mcm/year) from hydropower reservoirs in Africa, as of 2016. Water losses from waterbody surfaces prior to dam construction are not considered in the estimates.