Groundwater storage trend in headwater basins: shreds of evidence from the last decades in Minas Gerais state, Brazil

Changes in rainfall and temperature patterns can impact water security, mainly in tropical and subtropical regions. This study aimed to assess if climate change in Minas Gerais state, Brazil has impacted groundwater storage. Headwaters of four representative basins with minimum land use change were selected to quantify the effects of atmospheric forcing. Daily streamflow time series were used to assess changes in groundwater storage using the Brutsaert method. The Mann–Kendall and Sen tests were applied to evaluate the trends and determine the rate of change. 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 (Q_{7, 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. In contrast, at the Piracicaba sub-basin and Sapucaí sub-basin, it was not clear that climate changes can exclusively explain the decreasing trend in groundwater storage due to the changes in land use from native forest (Atlantic Forest and Cerrado) to pasture. 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 as their geomorphological aspects, i.e., soils, topography, soil-vegetation relationship, and hydrogeology, play a fundamental role in buffering the hydrological impacts. Our results can contribute to water resource management in Minas Gerais state, supporting decision-makers actions to minimize the effects.