The Water – Energy Nexus Of Hydropower. Are The Trade-Offs Between Electricity Generation And Water Supply Negligible?

Abstract:

Hydropower ranks first among renewable sources of power production and provides globally about 16% of electricity. While it is praised for its low greenhouse gas emissions, it is accused of its large water consumption which surpasses that of all conventional and most renewable energy sources (except for bioenergy) by far. Previous studies mostly applied a gross evaporation approach where all the current evaporation from the plant’s reservoir is allocated to hydropower. In contrast, we only considered net evaporation as the difference between current evaporation and actual evapotranspiration before the construction of the reservoir. In addition, we take into account local water stress, its monthly fluctuations and storage effects of the reservoir in order to assess the impacts on water availability for other users. We apply the method to a large dataset of almost 1500 globally distributed hydropower plants (HPPs), covering ~43% of global annual electricity generation, by combining reservoir information from the Global Reservoir and Dam (GRanD) database with information on electricity generation from the CARMA database. While we can confirm that the gross water consumption of hydropower is generally large (production-weighted average of 97 m³/GJ), other users are not necessarily deprived of water. In contrast, they also benefit in many cases from the reservoir because water is rather stored in the wet season and released in the dry season, thereby alleviating water stress. The production-weighted water scarcity footprint of the analyzed HPPs amounts to -41 m³ H₂O_e/GJ. It has to be noted that the impacts among individual plants vary a lot. Larger HPPs generally consume less water per unit of electricity generated, but also the benefits related to alleviating water scarcity are lower. Overall, reservoirs promote both, energy and water security. Other environmental impacts such as flow alterations and social impacts should, however, also be considered, as they can be enormous.