Challenging the complexity: assessing the performances of the convection-permitting configuration of the Regional Earth System Model RegCM-ES over northern Italy

Northern Italy is an area located in the northern part of the Mediterranean region where several factors make the modeling of its climate dynamics particularly challenging. The area is characterized by significant environmental gradients due to the complexity and high orography of  the Alpine arc surrounding the relatively flat area of the Po Valley, while strong air-sea interactions and deep water formation processes in the northern Adriatic Sea are associated with Bora wind episodes flowing over the basin. Moreover, the peculiar West-East oriented topography of the region drives the formation of a complex river network including the Po river, which is one of the major freshwater sources of the Mediterranean Sea.  Here we assess the performances of a state-of-the-art convection-permitting configuration of the Regional Earth System Model RegCM-ES specifically developed for the northern Italy region. The modeling tool components are : (i) RegCM5  with an horizontal resolution of 3 km and 50 vertical levels for the atmosphere, (ii) MITgcm  with an horizontal resolution of approximately 700 m and 59 vertical levels (non hydrostatic) for the ocean and (iii) CHyM with an horizontal resolution of approximately 1 km for the rivers. Model performances have been evaluated against observations and reanalysis datasets (available for the region) in a numerical experiment driven at the boundaries by ERA5 for the atmosphere and by the Copernicus Marine Service (CMS) reanalysis for the ocean. The model well captures  the spatial gradients and mean values of land and seawater temperature, precipitation and sea surface salinity. Still some deficiencies are observed such as a warm bias in summer over the western part of the Po Valley and an overestimation of precipitation over the Alps, although the latter is likely linked to the poor coverage of high altitude measurement stations in the area.  This configuration will be adopted in the future to produce high resolution climate projections for the region.