Suitability of ERA5-Land Reanalysis Dataset for Hydrological Modelling in the Alpine Region

Study region: The region of interest is the South-Tyrol in the southeastern Alps, Italy. A comparison of meteorological forcing is performed with reference to this region while hydrological simulations are conducted in the Passirio river basin. Study focus: The objective of this work is to evaluate the suitability of ERA5-Land reanalysis product as a reference dataset for hydrological modelling in topographically complex Alpine regions. ERA5-Land is compared with observational gridded dataset, obtained by means of the Kriging interpolation, available at two contrasting spatial resolutions a coarse grid size of 11 × 8 kilometres and a high-resolution grid size 1 × 1 kilometres. The hydrological coherence of the three datasets (ERA5-Land and the two observational datasets) with observed streamflow time series is then assessed with refer the Passirio/Passer river basin and to its nested and snow-dominated sub-catchment Plan/Pfelders. New hydrological insights for the region: The study assesses ERA5-Land’s suitability for hydrological simulations in the South-Tyrol region by comparing streamflow outcomes. At the annual scale, an overestimation of precipitation of about 40mm/month and a temperature underestimation of about 2.1 ◦C is reported. These discrepancies influence hydrological simulations, resulting in an overestimation of both streamflow and snow water equivalent. It is thus crucial to consider the limitations of ERA5-Land when using it as forcing for hydrological application in watersheds characterized by complex terrains, such as Alpine region.