Comportamento do armazenamento de água subterrânea em bacias de cabeceira de Minas Gerais

Abstract

Changes in rainfall and temperature patterns impact aquifer recharge in river basins, affecting water availability, especially during drought periods when baseflow maintains the necessary flows to meet water demands. The objective of this thesis is to evaluate if climate change is affecting water production and storage in the main basins of the state of Minas Gerais, and if so, since when and at what rate of change this is occurring; and to simulate groundwater storage throughout the century in future climate change scenarios. In the first part of the study, river basins located in the headwater regions of the state of Minas Gerais were analyzed, namely the Jequitinhonha, Piracicaba, São Francisco, Grande, and Sapucaí River basins. Potential evapotranspiration was calculated using the Thornthwaite method, and groundwater storage was calculated using the Brutsaert methodology for these basins. The Mann-Kendall test and Sen's coefficient were used to assess trends in historical series. According to the Mann-Kendall test, the most studied sub-basins showed an upward trend in temperature and evapotranspiration, while a nonsignificant trend was found for annual precipitation in some sub-basins. Mean annual streamflow, minimum streamflow over seven consecutive days (Q7,min), and groundwater storage (S) showed downward trends in most sub-basins. The Jequitinhonha sub-basin is the closest hydrological unit to the pristine conditions, indicating that changes in climate have impacted its hydrological response. The São Francisco and Grande River sub-basins are the most anthropized and showed the lowest reduction rates, showing that these sub-basins have a relevant resilience to climate change. In the second part of the study, the Grande and Jequitinhonha River basins were analyzed based on streamflow sections in their respective headwater regions. The MHD-INPE hydrological model was used for hydrological simulation, with a simulation horizon up to the year 2099, using climate data from the global climate models HadGEM2-ES, MIROC5, CanESM2 and BESM regionalized with the ETA/CPTEC model, in the RCPs 4.5 and 8.5 scenarios. The minimum annual groundwater storage was obtained using the Brutsaert method. And the existence of trends in the simulated flow and groundwater storage series was analyzed using the Mann-Kendall test and the Sen's coefficient. The results obtained in the calibration and validation phases of the MHD model were satisfactory in both basins. Analyzing the simulated flow series, significant reduction trends were observed in all projections in both basins. Regarding the minimum annual groundwater storage, significant reduction trends were also observed in all projections in both basins. The results obtained can contribute to water resource management in Minas Gerais, as they indicate the basins most vulnerable to the impacts of climate change. Thus, the results can assist in decision-making and the use of water resource management tools to ensure water availability in these basins in the future.