Cumulative impact of climate change and adaptation measures on Venice and its lagoon

Abstract Adaptation measures to climate change can generate unintended environmental consequences, particularly in vulnerable coastal systems. In the Venice Lagoon, the Mose mobile barrier system was designed to protect the city from sea-level rise and storm surges, still ensuring the lagoon-sea exchange. However, under climate change the frequency and duration of Mose closures will increase and this might modify lagoon water renewal and affect ecosystem properties. Here, we apply a high-resolution hydrodynamic model forced by downscaled climate projections to analyse trade-offs of adaptation measures by projecting lagoon conditions under two emission scenarios (RCP-4.5 and RCP-8.5) at mid (2045–2049) and end-century (2095–2099), with and without Mose operation. Results show that Mose effectively limits sea-level rise inside the lagoon, but significantly increases water renewal time (WRT). Under RCP-8.5 closures would reach ~ 248 days/year and one-third of the lagoon would require more than 20 days to renew its water. Under this scenario, extreme warming would occur, with summer temperatures higher than 30 °C for over three months per year and frequent, long-lasting marine heatwaves. Under RCP-4.5 these impacts are about halved, highlighting the critical role of global mitigation. Our findings demonstrate that while Mose can safeguard Venice from flooding, it also intensifies hydrodynamic confinement, which would combine with temperature changes to produce a severe cumulative pressure on the lagoon system. These results highlight that only the combination of complementary local measures and effective greenhouse-gas mitigation can support viable long-term adaptation pathways for coastal systems.