Simulation of the water table elevation in shallow unconfined aquifers by means of the ERA5 soil moisture dataset. The Umbria region case study

This paper concerns the simulation of the water table elevation in shallow unconfined aquifers where infiltration is assumed as the main mechanism of recharge. The main aim is providing a reliable tool for groundwater management, that satisfies water supply managers. Such a tool is a candidate as a physically based alternative to the use of empirical methods or General Circulation Models. It is based on the use of two widely available sets of data: the water table elevation measurements and soil moisture timeseries. In fact, the former are usually provided by government agencies on public websites whereas the latter are included in the atmospheric global datasets (reanalysis). It is worth noting that data from reanalysis are accessible to any citizen and organization around the world on a open access basis (e.g., Copernicus). In the proposed method, the measured water table elevations are correlated quantitatively with the water fluxes towards the aquifer evaluated using the soil moisture data from ERA5 reanalysis (provided by ECMWF) within a Richard equation-based approach. The analysis is executed using data from the Umbria region (Italy) on both a daily and monthly scale. In fact, these are the time intervals of interest for a proper management of groundwater resources. The proposed relationships include both a logarithmic and linear term and point out the possible different regimes of the shallow aquifers with regard to the recharge due to infiltration. These different mechanisms reflect in the different role played by the water fluxes towards the aquifer in terms of water table elevation changes according to the considered time scale.