AdriE: a high-resolution ocean model ensemble for the Adriatic Sea under severe climate change conditions

Abstract. The Adriatic Sea (eastern Mediterranean Basin) is traditionally considered a natural laboratory for studying a number of oceanographic processes of global interest, including coastal dynamics, dense water formation, and thermohaline circulation. More recently, the intensification of the effects of climate change and the increasing awareness of its possible consequences on the natural and socio-economic assets of the Adriatic Basin have opened new research questions and reframed most of the existing ones into a multi-decadal timescale. In this perspective, a description of the possible evolution of the physical oceanographic processes is one of the key requirements for addressing the multi-disciplinary challenges set by climate change, but up to now it has not been possible to combine, for this basin, a sufficiently high resolution in the process description with an estimate of the uncertainty associated with the predictions. This work presents an ensemble modelling approach (AdriE – Adriatic Sea Ensemble) for the kilometre-scale description of hydrodynamics in the Adriatic Sea in an end-of-century time frame. Addressing 3D circulation and thermohaline dynamics within the Regional Ocean Modelling System (ROMS), the ensemble consists of six climate runs encompassing the period from 1987 to 2100 in a severe RCP8.5 scenario forced by the SMHI-RCA4 regional climate model, driven by as many different CMIP5 general climate models made available within the EURO-CORDEX initiative. The climate ensemble is flanked by a dedicated evaluation run for the 1987–2010 period, in which SMHI-RCA4 has been driven by reanalysis fields approximating the best available boundary conditions, thus isolating the intrinsic sources of uncertainty in the RCA4–ROMS modelling chain. In order to allow a direct comparison, the assessment of the model skills in the evaluation run borrows, as far as possible, data and approaches used for the evaluation of a recent kilometre-scale, multi-decadal modelling effort for this region. The model performances are mostly aligned with the state-of-the-art reference. In particular, good results in describing the main features of marine heatwaves and cold spells, such as timing, intensity, and interannual variability, indicate that the AdriE ensemble can effectively be used for studies on the occurrence and effects of thermal extremes in the basin. Future projections suggest an increase in temperature and salinity at upper and intermediate depths, resulting in an overall decrease in water density and possibly in deep ventilation rates. Projected variations are stronger in summer and autumn, and in these seasons the ensemble range is larger than the spatial variability of the quantities and occasionally comparable with the intensity of the climate signal, highlighting the importance of an ensemble approach to treat the climate variability at this timescale. The dataset presented in this study, which can be used for the analysis of coastal and continental margin processes of general interest, is fully available upon request to the corresponding author, and monthly averages of the main quantities are available for each run on a dedicated Zenodo repository.