Groundwater recharge and associated uncertainty estimation combining multi-method and multi-scale approaches

Groundwater resource assessment is a major concern for water managers who have to balance water demands and resources at a basin or territory scale. One operational way to address this question is often to estimate only the part of recharge which is linked to precipitation. Many methods to estimate groundwater recharge are described in the literature, varying in terms of time scale and the nature of the data they treat. They do not always provide a suitable estimate of uncertainty. To obtain both a realistic estimation of groundwater recharge and a confidence interval at the hydrogeological basin scale, we propose a multi-method approach combined to a gridded water budget approach at the system scale. Firstly, ESPERE a recharge estimation tool combining several analytical methods has been developed and then applied to nine French hydrogeological case studies. The methods implemented in ESPERE are based either on climate data, discharges or piezometric levels time-series processing. This first approach addresses uncertainties linked to the estimation methods themselves. It also highlights the variability of recharge due to the interannual variability of meteorological data. Then, a spatialized approach was applied, in order to address spatial variability of meteorological data and parameters that control the water infiltration toward the aquifer. It relies on numerical treatments chaining cartographic data processing and water budget calculation with a resolution of 8 km. The combination of both approaches allows providing recharge time series at the systems scale, homogeneous recharge maps at the regional scale and uncertainty estimation associated to the calculation methods.