Aplicação do Índice Padronizado de Precipitação (SPI) e de Vazão (SSI) para análise de eventos de seca na bacia do Rio Suaçuí Grande/MG

Abstract

Fresh water is essential in all aspects of life and sustainable development; however, pressure on water resources has intensified and climate change has caused changes in the frequency and intensity of extreme weather events, such as floods and droughts. The Suaçuí Grande river basin, object of this study, is located in Minas Gerais state, having approximately 12,413 km² and facing critical situations of water scarcity. In order to study the current drought situation in the region, two indices were analyzed: the Standardized Streamflow Index (SSI) and the Standardized Precipitation Index (SPI), using observed flow and precipitation data from fluviometric and pluviometric stations, respectively, for the period from January 1985 to December 2019. To study the future projections, the SPI was analyzed, for the RCP8.5 scenario, through simulated precipitation data from the regionalized climate model Eta-HadGEM2-ES, for the period from 2025 to 2055. Analysis of duration, severity, intensity and frequency of drought events were carried out. Maps of the drought events frequency were also prepared to contribute to the spatial analysis. In addition, an assessment of the existing correlation between the SSI and the SPI was performed. From the analyses, it was possible to identify that, from mid-2010, more prolonged, frequent and intense drought events began to occur in the Suaçuí Grande river basin, and, from mid-2015, these drought events are more noticeable, presenting longer durations or recurrences. Rainfall stations located in municipalities with higher altitudes showed lesser intense negative values of SPI-12 since 2010. Through the SSI-12 it is possible to verify the occurrence of drought events even more intense than those identified through the SPI-12, especially from 2015 until the end of the historical series. It was observed that the correlations between the SPI and the SSI gradually increase according to the time scale, possibly indicating that changes in the rainfall regime strongly impact water availability in watercourses and reservoirs of the basin. When the historical drought events, simulated using the ETA-HadGEM2-ES model, are evaluated, it appears that the model identifies the most intense and lasting events that started in mid-2010, although it overestimates them and have difficulty to distinguish the stations located at higher altitudes. Regarding the projection of future drought, the model identifies that the predominance of drought events, that started from 2010, will extend until 2028. Regarding the frequency of extreme and exceptional drought events, it was found that these increase in the Malacacheta, São João Evangelista and Rio Vermelho stations, with the latter presenting the highest frequencies for these events, both in the observed dataset and for future projections. Regarding exceptional droughts, these will be more frequent in the future in almost the entire basin (87.5% of the seasons), especially in the southeast and southwest portions, with the exception of Água Boa.