Stochastic analysis of the recharge uncertainty of a regional aquifer in extreme arid conditions

The Pampa del Tamarugal Aquifer (PTA) is an important source of groundwater in northern Chile. Since the study area is situated in the Atacama Desert, the estimation of groundwater recharge based on conventional hydrological methods is subject to large uncertainties. To account for variations in the groundwater balance, caused by uncertainties in the average recharge rates, randomly generated recharge values with different levels of uncertainty are simulated using a groundwater flow model. Results show that evaporation and groundwater outflows are insensitive to the recharge uncertainty, while the storage terms can vary considerably. Considering current groundwater abstraction and random recharge rates, it is unlikely that the cumulative discharged volume from the aquifer, after a 45 years simulation period, will be larger than 12% of the estimated groundwater reserve. Simulated groundwater heads fluctuations due to uncertainties in the average recharge rates are more noticeable in certain areas. These fluctuations could explain anomalies in the observed groundwater heads in these areas.