Estimating groundwater recharge uncertainty for a carbonate aquifer in a semi-arid region using the Kessler's method

Abstract Groundwater recharge is an important hydrological parameter for the quantification of water budgets in order to better achieve a sustainable groundwater management. Such management is paramount in the southern region of Portugal because groundwater represents more than 75% of the public water supply, the water demand for irrigated agriculture and tourism industries is rapidly growing, and the region is severely threatened by droughts and extreme dryness. Nevertheless, the estimation of recharge to carbonate aquifers in semi-arid regions remains challenging. Uncertainty analyses are still scarce and the natural variability of recharge is unknown in most cases. The present work aims at estimating the recharge rate in carbonate aquifers of southern Portugal based on the Kessler method, identifying the confidence interval with known variability and reduced uncertainty. The outcome is a cost-free graphical tool that calculates an annual recharge rate per year, proving to be a reliable tool for annual recharge estimation and allowing to overcome the limitations of the chronological variability and data acquisition associated with other current methods. Acknowledging the confidence intervals of the annual recharge estimations can improve greatly the decision making process for the regional sustainable groundwater resources management.