A novel approach to generate very high resolution climate scenario for coastal areas

Climate change is evident in many aspects, among them there is the response of the sea to the progressive increase of the atmospheric temperature, the changes in the inland precipitation regimes and the surface wind field pattern. In this frame, the Mediterranean area is a hot spot, where atmosphere and sea interact with a high degree of coupling, and there is deep interest for its evolution.

Future climate scenarios for the Mediterranean are already available form a rich set of regional climate simulation, both for atmosphere and the sea. Anyway, stakeholders require information on future climate having a spatial resolution higher than that characterizing the regional scale. Furthermore, many local process of interaction between atmosphere, hydrosphere and sea, especially along the coasts and in shallow waters, have a poor representation in the available model outputs. Attempting to fill in the gap, downscaling is applied to regional climate and basin scale simulations.

In this work, we present a methodology to generate ensembles of high resolution downscaled sea state to the local scale, for the three main climate scenarios, namely RCP2.6, RCP4.5 and RCP 8.5. Using boundary conditions from EURO-CORDEX, MED-CORDEX ensembles, hydrological projections derived from inland precipitation scenarios, runs of a shallow water numerical model (SHYFEM) have been conducted to explore time windows for each decade in the future up to the end of the XXI century.

Starting from preliminary sensitive tests on the response of small spatial domains to the forcing and boundary conditions, we conclude that the effort to run very high resolution models, up to 10 m of horizontal resolution for a full and continuous secular time range, is not an efficient approach.

Instead, the quick response of the coastal system to the boundary and the forcing allows to generate a large set of local area sensitivity studies, with computational resources and times that are worth to be considered useful besides efficient.

This approach explores decadal time windows of many future scenarios with the spatial resolution required by a large spectrum of stakeholders who require details on future temperature, salinity and level along the coasts, in the lagoons and in the open sea facing the coastal areas.

In addition to the methodology, we present a summary of the results of its application to the northern Adriatic Sea, including the northeastern most lagoon. Furthermore, we show how those results become inputs for case studies on climate change impacts at the local scale and they support the definition of risk minimization actions, as requested by climate adaptation plans.

This work has been conducted with the contribution from the EU co-financing and the Interreg Euro-MED Programme, in the frame of MedSeaRise Project, exploiting the results of the Interreg IT-HR AdriaClim project.