Hydrodynamical and biogeochemical simulation of the Storm Gloria including major and minor river contributions

Extreme weather events and their associated storm surges are expected to become more frequent and intense in the Mediterranean Sea due to climate change and sea-level rise. Storm Gloria (January 19–24, 2020) hit the NW Mediterranean Sea with heavy rainfall, strong easterly winds, increase of sea-level rise and unprecedented wave height and wave periods. Many Catalan and French rivers increased their discharges by hundreds of times. The storm caused severe erosion, flooding, and destruction along the Catalan and Balearic coasts, marking the most devastating climate event in recent regional history. Understanding these occurrences and their impacts is crucial for safeguarding the densely populated coastal areas and their ecosystems.

The AquaInfra project (https://aquainfra.eu/) goal is to provide a digital infrastructure to properly study the role of continental water input into the near-coastal ocean to assess the risks and hazards to marine ecosystems. Within this framework, we are running a set of hydrodynamic and biogeochemical simulations using the BFMcoupler software, to investigate the impact of Storm Gloria on ocean dynamics and water quality. 

The BFMcoupler is a taylored interface coupling the hydrodynamic MITgcm and the biogeochemical BFM models. The model resolution is 1/128° and its domain extends from the Gulf of Lions in the north-east to the Gulf of Valencia in the south-west, including the Balearic Islands. Input data for the model is taken through AquaInfra’s EOSC digital infrastructure (https://eosc-portal.eu/), with MedSea Copernicus data for initial and boundary conditions, and ERA5 reanalysis hourly data for atmospheric forcing. The model also accounts for 17 Spanish and French rivers, including the Ebro and the Rhone. Rivers are modeled as small channels reproducing the depth of the riverbed close to the sea and velocity; salinity and temperature are imposed as open boundary conditions at river springs. River data are taken from local water agencies. We are currently working to include in the model: riverine, coastal discharge points and submarine groundwater discharges.

The experiments described here intend to determine the separated effects of fresh-water discharges from rivers and precipitation separately, and the combined effect. This will be done by a set of experiments in which daily values of riverine output and precipitation are replaced by their corresponding climatologies.

Preliminary results show, first, a decrease in temperature, salinity and chlorophyll in all river mouths when including real river discharge data compared to when using climate data. This effect propagated along the Catalan coast for the last days of the Gloria storm. An expected result caused by the increment of freshwater by rivers during the storm. We also observe how the regional characteristic north-south current, which evolves along the continental slope, is intensified by the strong winds, confining river effects to a few kilometers from the coast. Second, the effects of the Gloria heavy rainfall are observed all around the domain as a result of the positive buoyancy flux driven by the storm.

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(This work has received funding from the European Commission’s Horizon Europe Research and Innovation programme under grant agreement No 101094434.)