Intercatchment groundwater flow and unclosed water balance: a large-sample evaluation across European catchments

Intercatchment groundwater flow (IGF) quantifies groundwater fluxes across catchment boundaries, enabling the classification of catchments as either groundwater importers (gaining catchments) or exporters (losing catchments). It is a key component of the unclosed water balance equation that cannot be measured directly. The growing availability of large-sample datasets, gridded meteorological data, and satellite products provides an opportunity to develop a data integration framework to gain insights into this elusive hydrological variable.

This study focuses on the quantification of IGF for the European catchments included in the EStreams dataset. Precipitation and streamflow time series are provided in EStreams, while actual evapotranspiration data were gathered from the Global Land Evaporation Amsterdam Model (GLEAM) version 4. To identify the primary drivers of IGF, a random forest model was trained using a selection of catchment attributes as input variables, with IGF as the target variable. Permutation Variable Importance (PVI) was used to assess feature relevance, and the Maximal Information Coefficient (MIC) was calculated as an alternative method to quantify the relationship between catchment attributes and IGF.

Results of this work highlight the potential of a data integration framework to better characterize the unclosed water balance in European catchments and reveal key factors influencing IGF estimates.

ACKNOWLEDGMENTS: This study has been funded by a Humboldt Research Fellowship for Postdoctoral Researcher from the Alexander von Humboldt Foundation.