Groundwater Recharge Indicators at the European scale

One of the goals of the ERA4CS INDECIS project (http://www.indecis.eu/) is to use available climate datasets at the European scale to derive user-oriented indicators. In this framework, we adapted a methodology to compute the present and future groundwater recharge by precipitation at the European scale. This indicator of groundwater availability aims at supporting water resource management.

The scientific approach partly relies on two indexes related to precipitation infiltration at the watershed scale. The first one is the BaseFlow Index (BFI) which is considered as a fair approximation of the average infiltration coefficient for hydrogeological basins. The second one is the Network Development and Persistence Index (IDPR), a cartographic index calculated from the differences between the real river and the theoretical thalwegs networks. The IDPR provides a qualitative indication of infiltration versus runoff, and is now available at the European scale with a 50 m resolution. We computed the mean interannual BFI over the 1981 – 2010 period for more than 350 gauged and not influenced watersheds distributed over France, with various geological contexts and climates. These BFI values proved to be linearly correlated to the spatial average of the IDPR over these watersheds. The relationship between the two datasets established on these gauged basins was then applied to convert the European IDPR map into an effective precipitation infiltration ratio (EPIR) map.

The modelling process finally consisted in computing the effective precipitation at a daily time step on each cell of a mesh covering the European area. Three different water budget models were applied. The only parameter of these models is the soil water capacity provided by European Soil Data Centre. For the present period, the models were fed with the E-OBS datasets available on a 0.25 degree grid. Resulting time series were time-averaged and multiplied by the spatialized EPIR to provide a European map of annual potential recharge by precipitation infiltration. For the future periods, the same methodology can be applied. Ensemble simulations are in progress using EURO-CORDEX climate projections as input of the hydrological models.