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A native nested configuration of the ROMS model is implemented on the marine area between the Ligurian and Tyrrhenian basins, which includes the Tuscany Archipelago. Initial and boundary conditions are provided by the CMEMS Mediterranean Sea Physical Reanalysis product (1/16°), feeding the parent ROMS model (BLUE, 1/72°), in which a high-resolution grid is nested (PURPLE, 1/216°). Atmospheric forcing comes from a downscaled version of ERA5 reanalysis. Temperature and salinity profiles from gliders and floats, and HF-radar-derived surface currents, are compared to model outputs within the high-resolution area for the whole year 2017. Results show the downscaling procedure is able to reduce model errors for temperature profiles, whereas errors in salinity profiles remain comparable. However, the downscaled model cannot recover large errors inherited from the parent one. The mean bias largest values found in both temperature and salinity profiles may be explained by a model underestimation of the depth of stable stratification limit with respect to field data. Errors in surface currents are reduced for the downscaled dynamics and appear to be uncorrelated to the original CMEMS product, being surface dynamics less affected by initial condition than by atmospheric forcing. A simple scalar metric, to quantify the error in the surface current vector fields from observations and models, is proposed. The novel metric allows to better quantify the improvement gained by the downscaling procedure.

We analyze the effect of the assimilation of surface velocities from two HF-Radars (HFR) and satellite SST in an ocean circulation model covering the northwestern Mediterranean Sea.One HFR observes the area in front of Toulon (France), the other covers the area adjacent to the coast near La Spezia (Italy).The ROMS 4D-Var DA package is used to analyze a three-month period, from September to November 2020.The DA is implemented to have a sequence of 3-day assimilation windows, each followed by a 3-day forecast cycle in which the model evolves without adjustments.Boundary conditions are from the CMEMS Analysis-Forecast product and atmospheric forcing from ECMWF high resolution model (1/10 degree).The impact of the DA is quantified by comparing the analysis and forecast runs with a freerun that is unaffected by any assimilation procedure.The results show that both the analysis and the forecast perform better than the freerun considering the HFR and SST observations used in the assimilation procedure.Moreover, eulerian velocities derived from surface drifters are used as an independent dataset to further validate the quality of the DA output.Within the area covered by the HFRs, both the analysis and forecast surface velocities show greater agreement with the drifter data than the surface velocities from the freerun.However, in the rest of the domain, surface circulation improvements and deteriorations tend to balance out, and mean squared error and correlation values are comparable for analysis, forecast, and freerun.We also analyzed the impact of the observation typology and of the control vector on coastal transport for the upper 50 m at three transects.Two of them are located at the HFR areas and the other in between.Both HFR and SST data have a significant effect on surface transport increment.The HFR observations contribute to the change in the transport magnitude while the SST tends to change the velocity distribution along the transect, leaving the transport magnitude unchanged.Coastal transport is, in general, mostly affected by corrections to initial conditions in all three transects. The changes to the boundary conditions and atmospheric forcings have different importance depending on the transects analysed.

Local and global anthropogenic pressures due to climate change and to local uses and activities are exerting significant cumulative impacts to greater extents of the oceans and seas. Coastal ecosystems are particularly threatened by the intensity and coexistence of several marine uses and pressures, including sewage and urban constructions, tourism, ship traffic, fisheries and aquaculture. Assessment of pressures and the identification of mitigation measures are key urgent actions, as already highlighted by the EU Marine Strategy Framework Directive and the United Nations Sustainable Development Goal 14. The aim of this work, developed within the Interreg-Med project SHAREMED, is to systematize existing knowledge on threats and pollution, including those of transboundary origin, for long term strategies and common action marine spatial planning, jointly developed with stakeholders. The quest is to assess coexisting environmental threats, and their propagation in space and time, at proper spatial and temporal scales, according to the type and action of each stressor (i.e. global vs. local). Cumulative pressures are tackled within a dedicated Atlas comprising three sub-basinsins of the Mediterranean Sea: the North Adriatic Sea, the Sicilian Channel and the North-Western region. The Atlas integrates information generated at the best available resolutions by 1) in-situ sampling, 2) remote observations, 3) numerical models, and 4) focusing on target ecosystems and habitat forming species. These sub-basins are subjected to multiple local and larger scale (e.g. climate) pressures that propagate in space and time, and across political boundaries, that need to be addressed through coordinated actions, based on evidence-rooted common understanding. Interactions with relevant Stakeholders, solicited through an online survey, and meetings, were used to select target ecosystems and to identify the key relevant pressures. The Atlas is based on open-access databases and portals, literature reviews and from ad-hoc model simulations concerning marine heatwaves, ship traffic, oil pollution, marine litter and fishing efforts. We will present the main preliminary results and needs and gaps in observations related to marine ecosystems threats.

Marine plastic litter is one of the most significant signal of the impact of human activities on the marine environment. Therefore, improved methods and models are needed to better understand the distribution pattern of plastics (mainly microplastics) on the sea surface, along the water column, and on the seabed. So far, most plastics sampling campaigns have collected sea surface data, but these data were very scattered and mostly unrepresentative of the seasonal variability of their distribution. A comprehensive overview of the presence of plastic litter in marine enviroment must rely on models having the skill to better represent spatial patterns, interactions with marine ecosystems, and even predict the possible presence of plastic clusters at a specific time and position. Numerous studies adopted models of plastic transport which consider some sources of pollution (rivers, ports, ship routes) to determine plastic distribution in the open sea due to meteo-marine forcing. However, most of these models have not been validated against field data.In this presentation we show the results of a validation procedure of the modelled marine debris distributions expected in the North-Western Mediterranean between May and September 2019, through the comparison with field observations on the sea surface from campaigns carried out within the Interreg Med project Plastic Busters MPA. Marine debris observations show a significant variability, especially along the coasts, highlighting the need to employ a hydrodynamic model with a resolution much higher than that of basin-scale models. In the comparison between the observed and modelled surface plastic concentrations, the effect of model resolution will be specifically addressed.

The Mediterranean Sea is a prominent climate-change hot spot, with many socioeconomically vital coastal areas being the most vulnerable targets for maritime safety, diverse met-ocean hazards and marine pollution. Providing an unprecedented spatial and temporal resolution at wide coastal areas, high-frequency radars (HFRs) have been steadily gaining recognition as an effective land-based remote sensing technology for continuous monitoring of the surface circulation, increasingly waves and occasionally winds. HFR measurements have boosted the thorough scientific knowledge of coastal processes, also fostering a broad range of applications, which has promoted their integration in coastal ocean observing systems worldwide, with more than half of the European sites located in the Mediterranean coastal areas. In this work, we present a review of existing HFR data multidisciplinary science-based applications in the Mediterranean Sea, primarily focused on meeting end-user and science-driven requirements, addressing regional challenges in three main topics: (i) maritime safety, (ii) extreme hazards and (iii) environmental transport process. Additionally, the HFR observing and monitoring regional capabilities in the Mediterranean coastal areas required to underpin the underlying science and the further development of applications are also analyzed. The outcome of this assessment has allowed us to provide a set of recommendations for future improvement prospects to maximize the contribution to extending science-based HFR products into societally relevant downstream services to support blue growth in the Mediterranean coastal areas, helping to meet the UN's Decade of Ocean Science for Sustainable Development and the EU's Green Deal goals., peer-reviewed

Due to the semi-enclosed nature of the Mediterranean Sea, natural disasters and anthropogenic activities impose stronger pressures on its coastal ecosystems than in any other sea of the world. With the aim of responding adequately to science priorities and societal challenges, littoral waters must be effectively monitored with high-frequency radar (HFR) systems. This land-based remote sensing technology can provide, in near-real time, fine-resolution maps of the surface circulation over broad coastal areas, along with reliable directional wave and wind information. The main goal of this work is to showcase the current status of the Mediterranean HFR network and the future roadmap for orchestrated actions. Ongoing collaborative efforts and recent progress of this regional alliance are not only described but also connected with other European initiatives and global frameworks, highlighting the advantages of this cost-effective instrument for the multi-parameter monitoring of the sea state. Coordinated endeavors between HFR operators from different multi-disciplinary institutions are mandatory to reach a mature stage at both national and regional levels, striving to do the following: (i) harmonize deployment and maintenance practices; (ii) standardize data, metadata, and quality control procedures; (iii) centralize data management, visualization, and access platforms; and (iv) develop practical applications of societal benefit that can be used for strategic planning and informed decision-making in the Mediterranean marine environment. Such fit-for-purpose applications can serve for search and rescue operations, safe vessel navigation, tracking of marine pollutants, the monitoring of extreme events, the investigation of transport processes, and the connectivity between offshore waters and coastal ecosystems. Finally, future prospects within the Mediterranean framework are discussed along with a wealth of socioeconomic, technical, and scientific challenges to be faced during the implementation of this integrated HFR regional network., This study has been partially developed in the framework of the Interreg MED Strategic Project SHAREMED, co-financed by the European Regional Development Fund under the funding program Interreg MED 2014–2020. Website: https://sharemed.interreg-med.eu/ (last access: 31 March 2022). We are also grateful for the partial support of the (i) the project PO FEAMP 2014/2020 (Misura 2.51) funded by Regione Campania (Italy), (ii) the 2017 PRIN project EMME (Exploring the fate of Mediterranean microplastic: from distribution pathways to biological effects) funded by the Italian Ministry for Research (grant agreement no. 2017WERYZP), and (iii) the CMEMS-INSTAC phase II, which provides the context of the activities for HFR data harmonization, standardization, and distribution. Collaborative discussion on data management harmonization at the European level has also been carried out thanks to the contribution of the projects INCREASE (CMEMS Service Evolution Call for Tenders 21-SE-CALL1) and SeaDataCloud (EU-H2020 GA no. 730960).

The Mediterranean Sea is a prominent climate change hot spot, being their socio-economically vital coastal areas the most vulnerable targets for maritime safety, diverse met-ocean hazards and marine pollution. Providing an unprecedented spatial and temporal resolution at wide coastal areas, High-frequency radars (HFRs) have been steadily gaining recognition as an effective land-based remote sensing technology for a continuous monitoring of the surface circulation, increasingly waves and occasionally winds. HFR measurements have boosted the thorough scientific knowledge of coastal processes, also fostering a broad range of applications, which has promoted their integration in the Coastal Ocean Observing Systems worldwide, with more than half of the European sites located in the Mediterranean coastal areas. In this work, we present a review of existing HFR data multidisciplinary science-based applications in the Mediterranean Sea, primarily focused on meeting end-users and science-driven requirements, addressing regional challenges in three main topics: i) maritime safety; ii) extreme hazards; iii) environmental transport process. Additionally, the HFR observing and monitoring regional capabilities in the Mediterranean region required to underpin the underlying science and the further development of applications are also analyzed. The outcome of this assessment has allowed us to finally provide a set of recommendations for the future improvement prospects to maximize the contribution in extending the science-based HFR products into societal relevant downstream services to support the blue growth in the Mediterranean coastal areas, helping to meet the UN’s Decade of Ocean Science for Sustainable Development and the EU’s Green Deal goals.

Due to the semi-enclosed nature of the Mediterranean Sea, natural disasters and anthropogenic activities impose stronger pressures on its coastal ecosystems than in any other sea of the world. With the aim of responding adequately to science priorities and societal challenges, littoral waters must be effectively monitored with High-Frequency radar (HFR) systems. This land-based remote sensing technology can provide, in near real-time, fine-resolution maps of the surface circulation over broad coastal areas, along with reliable directional wave and wind information. The main goal of this work is to showcase the current status of the Mediterranean HFR network and the future roadmap for orchestrated actions. Ongoing collaborative efforts and recent progress of this regional alliance are not only described but also connected with other European initiatives and global frameworks, highlighting the advantages of this cost-effective instrument for the multi-parameter monitoring of the sea state. Coordinated endeavours between HFR operators from different multi-disciplinary institutions are mandatory to reach a mature stage at both national and regional levels, striving to: i) harmonize deployment and maintenance practices; ii) standardize data, metadata and quality control procedures; iii) centralize data management, visualization and access platforms; iv) develop practical applications of societal benefit, that can be used for strategic planning and informed decision-making in the Mediterranean marine environment. Such fit-for-purpose applications can serve for search and rescue operations, safe vessel navigation, tracking of marine pollutants, the monitoring of extreme events or the investigation of transport processes and the connectivity between offshore waters and coastal ecosystems. Finally, future prospects within the Mediterranean framework are discussed along with a wealth of socio-economic, technical and scientific challenges to be faced during the implementation of this integrated HFR regional network.

Coastal areas are experiencing an increasing anthropic pressure worldwide, especially due to port activities. In addition, valuable ecosystems such as Marine Protected Areas (MPA) might be located close to ports and be potentially subject to pollutant driven by the local current pattern. It is then fundamental to develop tools to analyze and quantify the tendency of a MPA to be affected by generic pollutant released from a port. Present work is based on a series of Lagrangian experiments carried out on a domain containing the port of Livorno and the Meloria Sholas MPA, located in the Tuscany Archipelago (Italy). The flow field employed to force the experiments is obtained from a downscaling modelling chain implemented with the 3D ROMS software. The top level is a 1.2 km low-resolution model covering the North-West portion of the Mediterranean basin which feeds with a one-way nesting algorithm a 400 m mid-resolution model for the Tuscany Archipelago, extending West of Corsica Island and up to the Gulf of Genova. The inner level of the modelling chain is a 50 m high-resolution coastal model (offline nesting) which covers the area of Meloria Shoals, the port, and their surroundings. Hydrodynamic simulations are carried out for one year. Initial conditions are provided by the CMEMS (1/24° res) model Analysis, as well as boundary conditions for the low-resolution model. Atmospheric forcing comes from the downscaling of the ERA-5 reanalysis dataset, consisting on the BOLAM model implemented on a 7 km grid of the Med-CORDEX domain, in which the MOLOCH model is nested on a 2.5 km spaced grid. Lagrangian numerical experiments are carried out considering the consecutive release of passive particles in the port area, at finite intervals for one year, following the trajectories for ten days. To estimate the degree of hydrodynamic connectivity between the port and the MPA and give a measure of the probability of contamination, the “oceanographic distance” is computed in several ways from the calculated trajectories. Preliminary results show the main transport pattern is mostly distributed alongshore, making the MPA less connected to the port compared to areas placed at the same distance.

In this work we present the results obtained through a dynamic downscaling of the ERA5 reanalysis dataset (hindcast) of ECMWF, using high-resolution meteorological and wave models defined on unstructured computation grids along the Mediterranean coasts, with a particular focus on the North-Western Mediterranean area. Downscaling of the ERA5 meteorological data is obtained through the BOLAM and MOLOCH models (up to a resolution of 2.5 km) which force an unstructured WW3 model with a resolution of up to 500 m along the coast. Models were validated through available meteorological stations, wave buoy data and X-band wave radars, the latter for the purposes of wave spectra validation.On the one hand, this allowed, by extracting the time series of some attack parameters of the waves along the coast, and according to the type of coast (rocky coasts, sandy coasts, coastal structures etc.), to compute the return periods and to characterize the impact of any individual storm. On the other hand, it is possible to highlight some trends observed in the last 30 years, during which recent research is showing an increasing evidence of some changes in global circulation at regional to local scales. These changes also include effects of wind rotation, wave regimes, storm surges, wave-induced coastal currents and coastal morphodynamics. For example, in the North-Western Mediterranean extreme events belonging to cyclonic weather-types circulation with stronger S-SE components (like the storm of October 28-30th 2018 and many others), rather than events associated with perturbations of Atlantic origin and zonal circulation, are becoming more frequent. These long-term wind/wave climate trends can have consequences not only in the assessment of long-term risk due to main morphodynamic variations (ie. coastal erosion), but also in the short-term risk assessment.This work was funded by the EU MAREGOT project (2017-2020) and ECMWF Special Project spitbran “Evaluation of coastal climate trends in the Mediterranean area by means of high-resolution and multi-model downscaling of ERA5 reanalysis” (2018-2020).