Analysis of indicators of climate extremes and projection of groundwater recharge in the northern part of the Rio de Janeiro state, Brazil

Climate change can affect directly the hydrological cycle and influence groundwater availability due to the direct or indirect impact on recharge and discharge processes. The present investigation focuses on groundwater recharge processes in a fluvial-deltaic aquifer in the northern part of the Rio de Janeiro state (Brazil), a region that relies on groundwater resources and where meteorological data indicate a shift from tropical humid climatic conditions to semiarid. The main objective is to understand how groundwater resources respond to the consequences of climate change on groundwater recharge, in order to improve groundwater management practices and guarantee quantitative and qualitative good status. Climate models' data and projections were used as a tool to provide a better understanding of how climate change can modify the dynamics in the studied groundwater system. The present climate indices for extreme temperature and precipitation (1961-1990) were examined in order to establish the current climatology for the study area, and the Thornthwaite-Mather hydrometeorological balance (TMHB) was used to calculate inputs to the aquifer. Projections for annual rainfall and air temperature for the period 2041-2070 obtained from Eta5km_HadGEM2-ES outputs for the Intergovernmental Panel on Climate Change scenarios RCP4.5 and RCP8.5 were used to estimate recharge to the aquifer using the hydrological code Visual Balan v2.0. Results revealed a tendency to air temperature increase and decrease in precipitation rate for the period of study. Consequently, there was a reduction of recharge in both IPCC scenarios used for the estimation, indicating a decrease in the groundwater resources stored in the region. These results place new challenges to guarantee sustainable groundwater management and the achievement of new aquifer system equilibrium to adapt to climate change impacts.