Fractured and porous aquifer recharge in semiarid regions and the relevance of soil covers: A review for Caetité area, Bahia, Brazil

Groundwater is a valuable natural resource in areas susceptible to arid and semiarid climates. In this research, the phreatic surface dynamics of shallow fractured and porous aquifers of Caetité, state of Bahia, Central Brazil, was investigated. Water level position was assessed by GRACE satellite data and 28 monitoring wells for the period from 2003 to 2024. Phreatic surface trends for all datasets are coherent to rainfall patterns described by precipitation moving averages and the Standardized Precipitation Index (SPI), respectively. The use of GRACE, however, is best applicable to soil hosted aquifers rather than to fractured systems. Recharge estimations considered the Water Table Fluctuation RISE methodology and vary depending on aquifer type. The annual storage variations obtained based on satellite and instruments installed in porous media (weathered rock and soil) suggests that 19–27 % of the year rainfall (130–177 mm/year) are annually converted into effective recharge. In systems composed solely of fresh fractured rocks rates drop to 3 % (24 mm/year). A relevant finding is the two-way effects of soil thickness in the recharge process. While pedon favors recharge on wetter conditions, it may diminish or equate annual storage variations to settings where no or thin soil covers are present. Data corroborates that aquifer recharge under semiarid conditions are sensitive to minor precipitation variations. Finally, it is proposed that geological setting must be considered when evaluating climate change impacts on groundwater, as infiltration is impacted by precipitation, evapotranspiration, and physiographical properties (relief pattern, geology, soil type and climate).