Mediterranean Marine Heatwaves: Past Variability, Future Evolution and Physical Drivers

The Mediterranean Sea is considered a “Hot Spot” region for climate change, and a significant rise in its annual mean SST has been already detected by the end of the 20th century. However, little is known about the occurrence of past Marine Heatwaves (MHW) in the basin, their physical drivers and their future evolution. Here, we use the latest version of a fully-coupled regional climate system (RCSM) model to study MHW characteristics between 1982-2017. Using a detection algorithm for long-lasting and large-scale summer events, we first examine their spatial variability and temporal evolution from surface to 55m depth. The analysis indicates an increase in duration and intensity of surface and deep MHWs with time. A preliminary analysis on the underlying mechanisms behind severe surface MHWs of the period is also performed. We then use an ensemble of dedicated RCSMs from the MED-CORDEX initiative, to project MHW evolution in the Mediterranean Sea surface over the course of the 21st century and under different greenhouse gas emission scenarios. Our results suggest longer and more severe events with higher global-warming rates. This study provides an overview of past and future MHWs in the Mediterranean basin, constituting key information for the marine ecosystems of the region, impacted already severely by these events.