A review of the data used to validate groundwater recharge maps created with GIS techniques over the past two decades

Groundwater recharge maps developed using GIS techniques are important tools that aid the identification of recharge zones. This map must be validated with field data. This study reviewed 63 articles published between 2007 and 2024 to examine the data used to validate these maps and identify the appropriate data for validation. About 50 % of articles reviewed contain non-validated maps, suggesting that many researchers did not do map validation. A total of 12 types of data have been identified to validate groundwater recharge maps, including electrical conductivity, total dissolved solids, stable isotope, and the magnitude of groundwater level fluctuations. Moreover, this review shows that 50 % (n = 6) of the identified data have high uncertainty and are therefore inappropriate for validation, including groundwater level, nitrate concentration, well yield, and aquifer transmissivity. Data reflecting groundwater residence time are more appropriate for validation.