Isotopic and Remote Sensing-Based Characterisation of a Rainfall Event over Western Sierra de Gádor (Spain): Implications for Carbonate Aquifer Recharge

Abstract

Stable water isotopes are widely recognised as essential tools to trace processes within the hydrological cycle and to disentangle complex phenomena, such as regional–local atmospheric patterns, infer water balances or characterise the aquifer recharge. In this work, we characterised two post-summer precipitation events over the western sector of Sierra de Gádor through the analysis of the rainwater δ18O and δ2H ratios, ionic composition and, complementarily, remote sensing products to define the atmospheric circulation during the rainfall episodes. This information enabled us to discern the moisture source, formation conditions and orographic influence on the rain episodes, and to better define the origin of the groundwater recharge and its dynamics in the study area. Although the samples share a common moisture source (W Mediterranean), they display substantial differences in their isotopic compositions. Such differences are attributable to sub-cloud evaporation processes that mask their Mediterranean origin, and to the strong influence of the orography on the hydrochemical and isotopic characteristics of the rainfall at the local level. The groundwater presents a very stable isotopic content and is strongly depleted in heavy isotopes, evidencing that most of the aquifer recharge takes place at very high altitudes and primarily during winter, when the influence of evaporation is attenuated.