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

Abstract. With its complex and peculiar meteo-oceanographic dynamics and the coexistence of diverse socio-economic activities and pressures with outstanding cultural heritage and environmental assets, the Adriatic basin (Mediterranean Sea) has traditionally been considered as a natural laboratory for marine science in its broadest meaning. In recent years the intensification of the effects of climate change, together with the increasing awareness of its possible consequences and of the knowledge gaps hampering a long-term response, have opened new questions and reframed most of the existing ones into a multi-decadal time scale. In this perspective, a description of the possible evolution of the physical oceanographic processes is the baseline 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 end-of-century, kilometre-scale ensemble modelling approach for the description of ocean processes in the Adriatic Sea. Addressing 3-D 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 better available boundary conditions, thus isolating the intrinsic sources of uncertainty of 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-art reference, with particularly encouraging results in terms of description of Marine Heat Waves and Cold Spells. 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 time scale. Monthly averages of the main quantities are available for each run on a dedicated Zenodo repository, and subsets of the full modelling dataset can be requested to the corresponding author.