Origin and type of rainfall for recharge of a karstic aquifer in the western Mediterranean: a case study from the Sierra de Gador-Campo de Dalias (southeast Spain)

Isotope signatures in precipitation from the Global Network for Isotopes in Precipitation around the Mediterranean basin and literature data are compared with isotopic data from a large karstic aquifer in southeast Spain to explain the origin and type of the precipitation events dominating recharge. Analysis of the deuterium excess d at the scale of the Mediterranean basin and at the regional scale allows us to understand the isotopic context of the study area: Campo de Dalias and the Sierra de Gador (Almerfa province). The origin of precipitation can be determined from its d value. The d value changes as a function of the initial evaporation condition. It depends on the relative humidity and temperature during the evaporation producing the water vapour of the clouds. The water vapour, which dominates the study area, is generated in two areas: the Atlantic Ocean (d = 10 parts per thousand) and the western Mediterranean basin (d = 15 parts per thousand). With increasing precipitation volume, the western Mediterranean character dominates. These heavier storms contribute mainly to recharge, as illustrated by the d value of 13.6 parts per thousand in deep groundwater of the Campo de Dalias. Weighted d values increase with the volume of precipitation, giving a significant relationship for the southern and eastern coasts of the Iberian Peninsula. This selectivity of d to monthly precipitation was used to estimate the return period of precipitation leading to aquifer recharge at 0.9-4.9 years. Moderate rainfall, which occurs more frequently, still represents similar to 60-90% of the total precipitation. One of the challenges to meet ever-growing water demands is to increase recharge from moderate events yielding intermediate quantities per event, but forming the bulk of the annual precipitation. Copyright (c) 2006 John Wiley & Sons, Ltd.