Abstract
Groundwater recharge quantification is essential for sustainable groundwater resources management, but typically limited to local and regional scale estimates. A high-resolution (1 km × 1 km) dataset consisting of long-term average actual evapotranspiration, effective precipitation, a groundwater recharge coefficient, and the resulting groundwater recharge map has been created for all of Europe using a variety of pan-European and seven national gridded datasets. As an initial step, the approach developed for continental scale mapping consists of a merged estimate of actual evapotranspiration originating from satellite data and the vegetation controlled Budyko approach to subsequently estimate effective precipitation. Secondly, a machine learning model based on the Random Forest regressor was developed for mapping groundwater recharge coefficients, using a range of covariates related to geology, soil, topography and climate. A common feature of the approach is the validation and training against effective precipitation, recharge coefficients and groundwater recharge from seven national gridded datasets covering the UK, Ireland, Finland, Denmark, the Netherlands, France and Spain, representing a wide range of climatic and hydrogeological conditions across Europe. The groundwater recharge map provides harmonised high-resolution estimates across Europe and locally relevant estimates for areas where this information is otherwise not available, while being consistent with the existing national gridded datasets. The Pan-European groundwater recharge pattern compares well with results from the global hydrological model PCR-GLOBWB 2. At country scale, the results were compared to a German recharge map showing great similarity. The full dataset of long-term average actual evapotranspiration, effective precipitation, recharge coefficients and groundwater recharge is available through the EuroGeoSurveys' open access European Geological Data Infrastructure (EGDI).
Highlights
Groundwater plays a vital role for humans and for ecosystems worldwide
The bias is not dominated by differences in precipitation input, since it occurs for the national pilots, where precipitation data are shared between the Pan-European maps and the national pilots
The validation indicates that the actual evapotranspiration from the combination of Budyko and satellite data (Eact,Budyko/Satellite) is higher than the Eact estimates used for calculating the effective precipitation for the national pilots
Summary
Groundwater plays a vital role for humans and for ecosystems worldwide. It is employed to supply irrigation, drinking water and industrial demands, and sustains wetlands, rivers and other groundwater-dependent ecosystems. The rate of groundwater recharge, expressing the annual renewal potential, is a key hydrological variable for quantifying available water resources, safe yields and vulnerability to climate variability and change (Riedel and Weber, 2020). It is largely controlled by: precipitation, evapotranspiration, surface infiltration, land cover and soil hydraulic characteristics (Mohan et al, 2018). It is highly variable in time and space, mainly across climate gradients, and as a result of patterns in topography, soil, land cover and geology (MacDonald et al, 2021; Moeck et al, 2020; Xu and Beekman, 2019)
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