Water scarcity footprint of hydropower based on a seasonal approach - Global assessment with sensitivities of model assumptions tested on specific cases.

According to ISO 14046 the quantification of the water scarcity footprint (WSFP) of hydropower reservoirs has to consider (1) the evaporation of water from the surface of the reservoir, (2) the baseline evaporation of water of the same area before the reservoir has been built, and (3) the water scarcity index of the location of the reservoir on a spatially and temporally explicit level. When a reservoir has a storing function, e.g., for irrigation in the dry season, monthly water scarcity indexes have to be used in order to calculate the WSFP, since storage in wet seasons and release in dry seasons can counteract water scarcity and lead to a reduction of overall water scarcity in the watershed. This paper builds on previous research regarding detailed hydropower modeling and extends the water scarcity assessment to include and advance new methods for identifying sensitivities in monthly WSFP of hydropower due to the choice of impact assessment methods. We applied the global analysis to 1473 hydropower plants covering >100 countries, and added a detailed assessment for a subset of important power plants to discuss the limitations of global assessments. We thereby provide the most complete WSFP of global hydropower with state-of-the-art methods, assess the robustness of the global model and different methodological choices, and provide new monthly average AWARE CFs on watershed level. The results show that water scarcity can often be mitigated if the net evaporation is compensated by the storage effects. The two water scarcity metrics applied lead to larger differences than expected, since the monthly dynamics of dams can lead to stronger differences than the differences in the applied water scarcity factors. The new insights help to better understand the WSFP of hydropower and its uncertainties.