Understanding the hydrological drought processes in the Paraná River Basin.

Brazil has endured the worst droughts in recorded history over the last decade, resulting in severe socioeconomic and environmental impacts. The country relies heavily on water resources, with 77.7% of water consumed for agriculture (irrigation and livestock), 9.7% for industry, and 11.4% for human supply. Hydropower plants generate about 64% of all electricity consumed. One of the most impacted basins was the Paraná River basin It concentrates a third of the Brazilian population in urban centres such as São Paulo, the largest city in Latin America, thus it is the river basin with the greatest demand in the country. This basin is also the most important in hydropower generation, by the highest install capacity for hydropower; 57 reservoirs in the main steam and its tributaries (Grande, Paranaíba, Tietê, Paranapanema and Iguaçu Rivers), with Itaipu having the largest installed capacity (14,000 MW). This study aimed to advance the state of knowledge regarding hydrological drought patterns in the Paraná River Basin for improved monitoring and forecasting.

Droughts, like all hydrometeorological processes, are multivariate processes, that is, they are the result of the interaction of multiple hydrometeorological, climatic, and anthropogenic variables, among others. Therefore, several studies have shown the need to consider a multivariate approach to analysis and modelling drought events, which allows a better evaluation of the characteristics and conditions of its.

In this study we applied: i) well know univariate drought index: SPI, SPEI and SSFI; ii) a multivariate index, obtained through the Copulas Theory and; iii) potential soil moisture conditions obtained through the Normalized Terrain Model HAND, to understand and characterized hydrological droughts in the Paraná River Basin and Subbasins. We used rainfall data from CHIRPS, streamflow data obtained from the Brazilian National Electrical System Operator (ONS) and the National Water and Sanitation Agency (ANA), the SPEI global drought monitor dataset and HAND MERIT dataset (90 m spatial resolution).

The results show that the hydrological droughts in the last decade of 1981–2021, were the most severe and intense. Among the indices, SPEI, SSFI and the multivariate index, presented the strongest evidence, at time scales of 12, 24, 36 and 48 months. The multivariate index together with HAND information allow us to understand better the process of developing, duration, and recovery of drought events.