Performance of three reanalyses in simulating the water table elevation in different shallow unconfined aquifers in Central Italy

Water table elevation is a key feature for identifying the groundwater behaviour. Accordingly, appropriate measurements-in terms of both frequency and spatial distribution-play a crucial role for capturing the aquifer response to recharge and withdrawals. However, numerical models simulating the main features of the behaviour of the water table elevation may help groundwater management, as an additional tool. In this article, soil moisture data from three well-established global reanalyses (ERA5, CFS, and JRA-55) are used for evaluating the flux in the vadose zone towards shallow unconfined aquifers, Fg$$ {F}_g $$, in the Umbria region (central Italy). Then, according to the methodology proposed in Bongioannini Cerlini et al. (2021), where for the considered aquifers most of the recharge derives from the unsaturated zone, Fg$$ {F}_g $$ is used for simulating the water table evolution in time. With the aim of assessing which reanalysis is the most appropriate in simulating the evolution of groundwater levels, the properties of the correspondent land surface models (LSM) are examined, as they provide Fg$$ {F}_g $$. For the considered aquifers, the analysis of the performance of the selected reanalyses confirms the validity of the proposed approach. Moreover, it points out the crucial role of the spreading of the water table elevation with respect to its mean value, as a significant parameter for selecting the most adequate reanalysis to use. In addition, the role in the LSM of the explored soil depth, hydraulic conductivity curve, and spatial resolution is highlighted. These results, in line with recent literature on the performance of the reanalyses, suggest to extend future work to other regions of the world.