Sensitivity analysis of groundwater balance terms as a function of uncertainty in groundwater recharge

The Pampa del Tamarugal Aquifer (PTA) is one of the most important sources of water in northern Chile. Situated in the Atacama Desert, the estimation of the 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, random values of the recharge were generated, and simulated using a groundwater model. Results show that evaporation and groundwater outflows are insensitive to the uncertainties in the recharge, while storage is very sensitive. Considering projections of groundwater abstractions and random recharges, it is unlikely that the cumulative discharge 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 recharge are more noticeable in certain areas, likely explaining the anomalies in the observed groundwater heads in these areas.