Annual amount of water evaporated from artificial lakes and reservoirs. The evaporation to take into account is the net evaporation (evaporation - precipitation). A portion of flow generated internally is not entirely collected by the hydrological system. With regard to the evaluation of resources, evaporation from wetlands, natural lakes and rivers is a reducing factor of the entire flow generated. However this reduction of runoff should not be considered entirely as a loss"" because it corresponds partly to the needs of nature, specifically those needs of aquatic systems.