The complex response of the river-sea continuum systems to the climate extremes: insights from the Po delta

Compound flooding and drought events are becoming increasingly frequent and intense across many catchment areas draining into the Mediterranean basin. The interconnected nature of catchment hydrology and marine hydrodynamics processes poses significant challenges to advancing the numerical modelling of the catchment-sea continuum systems and to provide a comprehensive representation of the complex response of deltas to the climate extremes. To address these challenges, we used a seamless numerical modelling of the river-sea continum based on a Finite Element code (SHYFEM-MPI – Micaletto et al. (2022), Verri et al. (2023)). The SHYFEM-MPI experimental settings has been progressively refined with generalized vertical coordinates and wet and dry capabilities, aiming at deepening the understanding of compound flooding and drought events occurring in the Po Delta system, which is Italy's longest river and the second-largest freshwater source for the Mediterranean basin. Therefore, a four-year experiment (2019–2023) was conducted to simulate significant events, including the November 2019 storm surge and river flood event and the July 2022 record breaking drought. Model findings were validated against available in-situ and satellite observations allowing a detailed tracking of the salt wedge intrusion length during the compound extremes. Based on the results obtained, we explored the role of non-linear combination of multi-scale and cross-scale forcing mechanisms to enhance the modeling accuracy and the understanding of the complex physical processes underlying such extreme events.