Inter-basin water transfers under changing climate and land use: Assessing water security and hydropower in the Paraíba do Sul River basin, Brazil

The intensification of climate extremes and land uses poses a major challenge for water managers, especially in heavily populated basins with large reservoirs, multiple uses, and inter-basin transfers. In this study, we analyzed water security in the Paraiba do Sul River basin, responsible for supplying a significant fraction of the needs of Brazil's two largest metropolitan areas through water transfer. Unless existent studies emphasize aspects of water scarcity disregarding other competitive water use, we considered the impacts on hydropower generation in a fully integrated modeling framework, which includes reservoir operation rules. To achieve this, we integrated future projections of land uses, global climate change (RCP 4.5 and RCP 8.5), and water demand for the period 2016-2055. Most of the climate change scenarios suggested a reduction in the frequency of both high and low flows, by nearly 25%, which resulted in an increase in flow regularization in the main basin's reservoirs. An undesirable consequence of those trends was the reduction of hydropower generation. Regarding water supply to the metropolis outside the basin, results indicated a possibility of a more contentious water governance scenario. The long-term sustainability of the basin's water resources will require implementing policies to enhance water use efficiency and reuse, in combination with other renewable energy sources.