Georg Umgiesser

Venice and its lagoon form a tightly coupled coastal socio-ecological system in which urban fabric, cultural heritage, lagoon ecosystems and regional infrastructures jointly determine vulnerability and resilience to sea-level rise. As relative sea level continues to increase due to climate change and subsidence, adaptation in Venice cannot be limited to incremental risk reduction but requires transitions between fundamentally different strategies.This contribution applies an adaptation pathways perspective to the Venice–lagoon system to examine how the available solution space decreases under rising sea level. Four adaptation strategies are considered: an open-lagoon configuration based on mobile barriers and accommodation measures, ring-diking that isolates the historic city and other settlements from the lagoon, (closed-lagoon configuration with permanent coastal barriers), and retreat through relocation or abandonment. The analysis focuses on how physical constraints, ecological impacts, social acceptability and long lead times interact to shape transitions between these strategies as sea level rise continues.The Venice case illustrates how climate and geo-processes, infrastructures, available technical solutions and cultural values condition the timing and characteristics of adaptation tipping points, beyond which strategies can no longer meet their intended goals. By explicitly linking alternative strategies to distinct socio-ecological transformations of the city and its surrounding environment, the pathways approach helps clarify trade-offs, irreversibilities and decision time windows for urban transformation under deep uncertainty.The results highlight the importance of early, anticipatory planning for coastal cities facing long-term sea-level rise, and demonstrate how geoscience-informed adaptation pathways can support governance of transformative change in complex urban regions.

The substantial risks posed to Venice and its lagoon by ongoing and projected sea-level rise require unprecedented long-term adaptation strategies. With present insufficient greenhouse gas mitigation policies, the current open lagoon strategy, with mobile barriers and multiple accommodation measures, is likely to encounter hard limits within the current century. Follow-up strategies could be based either on ring-dikes, isolating the city from the rest of the lagoon, or on a closed lagoon with permanent coastal dams separating it from the sea. Relocation of monuments to a suitable inland area and abandonment of Venice would be the only remaining strategy for sea-level above 10-15 m. Indicative adaptation costs increase with sea level rise from less than 1 to more than 30Ge. Abandonment might become unavoidable in the 22nd century under current climate policies and an Antarctic ice-sheet collapse, a risk that could still be avoided by a rapid reduction of greenhouse gas emissions.

Lake Albano is a monomictic volcanic crater lake in Central Italy with CO₂-rich waters presenting CO₂ concentration varying over time. Depending on the period of the year, the lake is characterized by strong stratification or rather overturning events. In the warm season, the heating of the surface water results in a highly stratified vertical density profile, while in the cold season, the surface water cooling leads to a potential vertical instability of the water column. In this case, a partial/deep overturning of the lake water column may occur with the degassing in the atmosphere of the CO₂ which was accumulated as dissolved species in the deep water layers following seismically induced gas recharge, months to years before. Such a process has been periodically observed in Lake Albano in the past and could pose a potential hazard to the surrounding environment and population. A 3D numerical model is implemented to investigate the lake dynamics and the occurrence of overturning events. The model is validated and calibrated using both historical observations and measurements acquired during this study. These include temperature and salinity profiles from the deepest central portion of the lake, surface water temperature time series recorded by sensors installed on the lake shores, mounted on remotely operated vehicles, and on low-cost, innovative, self-powered drifting buoys. The latter have also been used to assess the modeled surface circulation of the lake.

Lake Albano is a monomictic volcanic crater lake in Central Italy with CO₂-rich waters presenting CO₂ concentration varying over time. Depending on the period of the year, the lake is characterized by strong stratification or rather overturning events. In the warm season, the heating of the surface water results in a highly stratified vertical density profile, while in the cold season, the surface water cooling leads to a potential vertical instability of the water column. In this case, a partial/deep overturning of the lake water column may occur with the degassing in the atmosphere of the CO₂ which was accumulated as dissolved species in the deep water layers following seismically induced gas recharge, months to years before. Such a process has been periodically observed in Lake Albano in the past and could pose a potential hazard to the surrounding environment and population. A 3D numerical model is implemented to investigate the lake dynamics and the occurrence of overturning events. The model is validated and calibrated using both historical observations and measurements acquired during this study. These include temperature and salinity profiles from the deepest central portion of the lake, surface water temperature time series recorded by sensors installed on the lake shores, mounted on remotely operated vehicles, and on low-cost, innovative, self-powered drifting buoys. The latter have also been used to assess the modeled surface circulation of the lake.

Lake Albano is a monomictic volcanic crater lake in Central Italy with CO₂-rich waters presenting CO₂ concentration varying over time. Depending on the period of the year, the lake is characterized by strong stratification or rather overturning events. In the warm season, the heating of the surface water results in a highly stratified vertical density profile, while in the cold season, the surface water cooling leads to a potential vertical instability of the water column. In this case, a partial/deep overturning of the lake water column may occur with the degassing in the atmosphere of the CO₂ which was accumulated as dissolved species in the deep water layers following seismically induced gas recharge, months to years before. Such a process has been periodically observed in Lake Albano in the past and could pose a potential hazard to the surrounding environment and population. A 3D numerical model is implemented to investigate the lake dynamics and the occurrence of overturning events. The model is validated and calibrated using both historical observations and measurements acquired during this study. These include temperature and salinity profiles from the deepest central portion of the lake, surface water temperature time series recorded by sensors installed on the lake shores, mounted on remotely operated vehicles, and on low-cost, innovative, self-powered drifting buoys. The latter have also been used to assess the modeled surface circulation of the lake.

Lake Albano is a monomictic volcanic crater lake in Central Italy with CO₂-rich waters presenting CO₂ concentration varying over time. Depending on the period of the year, the lake is characterized by strong stratification or rather overturning events. In the warm season, the heating of the surface water results in a highly stratified vertical density profile, while in the cold season, the surface water cooling leads to a potential vertical instability of the water column. In this case, a partial/deep overturning of the lake water column may occur with the degassing in the atmosphere of the CO₂ which was accumulated as dissolved species in the deep water layers following seismically induced gas recharge, months to years before. Such a process has been periodically observed in Lake Albano in the past and could pose a potential hazard to the surrounding environment and population. A 3D numerical model is implemented to investigate the lake dynamics and the occurrence of overturning events. The model is validated and calibrated using both historical observations and measurements acquired during this study. These include temperature and salinity profiles from the deepest central portion of the lake, surface water temperature time series recorded by sensors installed on the lake shores, mounted on remotely operated vehicles, and on low-cost, innovative, self-powered drifting buoys. The latter have also been used to assess the modeled surface circulation of the lake.

The coastal areas of Emilia-Romagna (Northern Italy) are characterised by different environments, including sandy beaches and the transitional areas of the Po Delta. The low-lying sandy beaches render the local coastlines highly vulnerable to extreme meteo-marine events, which can have serious consequences such as marine ingression, coastal erosion and flooding. The Regional Agency for Prevention, Environment and Energy of Emilia-Romagna (Arpae) manages an Operational Early Warning System for Coastal Risks (EWS) that provides daily forecasts, integrated with a Regional Observing Network. The EWS consists of different implementations of a meteorological model (COSMO), a wave model (SWAN-MEDITARE), an oceanographic model (Adriac, based on COAWST) and a morphodynamics model (XBeach). Adriac oceanographic forecasts are carried out on a regular grid with a fixed resolution (1 km). Structured grids, however, struggle to accurately resolve short scale physical processes and complex bathymetries, especially given the complexity of the regional coastline.. For this reason, a very high resolution hydrodynamic model for the Po Delta and the Emilia-Romagna coast, extending inland up to the Pontelagoscuro station (river flow measurements), was developed. The model (shyfER) is based on the SHYFEM code that solves the hydrodynamic equations on unstructured meshes. It provides daily forecasts (+72 hours) of total water level, salinity, temperature and currents.As salt intrusion in the Po Delta is an important phenomenon that has increased in frequency and intensity in recent years, the model performance in terms of salt wedge representation is currently being evaluated. Furthermore, tests were conducted in terms of microbiological dispersion simulations by coupling the model with BFM (Biogeochemical Fluxes Model) in a 0-dimensional setting.Finally, it is crucial not to overlook the significance of observations, as they enable accurate calibration and validation of models. Thanks to European funding, Arpae has been able to expand its marine-coastal observation network, which currently consists of three tide gauges (at Porto Garibaldi, Cattolica and Cervia), a wave buoy with a current-meter (at Cesenatico) and various multiparametric stations. In addition, a regional monitoring network of eight webcams (camERa) has been installed along the regional littoral allowing continuous monitoring of the coastal areas.Arpae-SIMC is currently involved in several projects to maintain and update the system, including the DIRECTED project (Horizon 2020), which focuses on the "power" of the Early Warning Systems. Together with the Civil Protection of the Emilia-Romagna Region (ARSTPC-ER) Arpae leads the Real-World Lab in Emilia-Romagna.

We are developing a new regional coupled ocean-atmosphere-wave model to study the air-sea interaction during intense meteo-marine events such as mesoscale cyclones and tropical-like cyclones. The coupled model is based on the following open-source community model components: (1) an ocean component with the SHYFEM finite element coastal ocean model, (2) a wave component with the unstructured WW3 spectral wave model, (3) an atmospheric component with the Weather Research and Forecasting model (WRF). The wave and the ocean components are hard-coupled and run on the same triangular grid. The resulting ocean-wave and atmosphere components are coupled through the Earth System Modelling Framework library (ESMF), an integrated coupling framework which leads to very clean, abstract and efficient coupled models. The implemented coupler can handle explicit and semi-implicit coupled time-stepping schemes. With this instrument we study the interaction of tropical cyclone-like vortices with the sea. We show with simplified experiments how this feedback affects the trajectories and the intensity of the vortex as well as the sea-surface temperature and the ocean circulations. We show our model scales well compared to the baseline (uncoupled) runs of the single components. It can be thus applied to large scale configurations with high resolution. We focus on a series of storm events that occurred on the Mediterranean Sea: storm Vaja in 2018, Medicane Ianos in 2020 and a mesoscale cyclone in the northern Adriatic Sea occurred in 2019. The results derived from the coupled model are compared with those from the simulations using either only the ocean or the atmospheric model, with external forcing (uncoupled). The comparisons made against observational data show that the coupled model outperforms the uncoupled one.