A preliminary implementation of SCHISM model in Basque Country

In the broader context of the climate emergency facing the Autonomous Community of the Basque Country (BAC), the maritime-coastal area is highly sensitive to the potential increase in extreme events. Among the main adaptation measures to this situation are early action systems that help minimize the impact. One of the key components of these systems is the prediction tools used in the maritime-coastal field. Specifically, the Basque Meteorology Agency (Euskalmet) has been deploying different wave and ocean models (WW3, SWAN, WAM, ROMS, … ) for over 15 years to support our operational needs. These needs, which have grown in complexity and detail over the years, include increasing resolution closer to the coast, in shallow waters and estuaries, thereby improving the prediction of local impact.

In this contribution, we present one of the strategies adopted to achieve these objectives, particularly the incorporation of a new component into this maritime-coastal modeling system for the Basque region, SCHISM.

The SCHISM modeling system (Semi-implicit Cross-scale Hydroscience Integrated System Model) is an open-source, collaborative modeling system. It is based on unstructured grids and is designed to simulate baroclinic circulation across any spatial scale, from rivers to oceans. It uses a semi-implicit finite element/finite volume method with an Eulerian-Lagrangian algorithm to solve the Navier-Stokes equations (in their hydrostatic form), addressing a wide range of physical and biological processes. Mass conservation is applied using the finite volume transport algorithm.

Two key features of SCHISM that make it attractive for Basque Country coastal area are: a) its use of irregular grids, which allows for different mesh resolutions at varying distances from the coast (finer at the shore and coarser offshore), and b) the ability to integrate river flow and even predict upstream behavior, which potentially enables its use in predicting tidal-river floods.

In this contribution, we present the main steps taken to implement the system, including the selection of parameterizations, the guidelines for pre-processing and post-processing of the data, and various validation and verification exercises of the system. Particular attention is given to aspects crucial for determining overflow indices within the context of 'maritime-coastal risk: impact on the coast,' addressing key factors for both operational and research purposes across various projects including Regions4Climate.