Far-Future Climate Projection of the Adriatic Marine Heatwaves: a kilometre-scale experiment under extreme warming

Abstract. The impact of a far-future extreme warming scenario on Adriatic marine heatwave (MHW) characteristics—including intensity, duration, spatial extent, and associated environmental drivers—is assessed using the Adriatic Sea and Coast (AdriSC) kilometre-scale atmosphere-ocean model. The main aim of this study is to evaluate the added value and limitations of the Pseudo-Global Warming (PGW) approach used to force the far-future AdriSC simulation, in projecting Adriatic MHWs. In line with existing knowledge, the results indicate a significant increase in MHW intensity along with a notable expansion in spatial coverage, particularly in the central and eastern Adriatic. Seasonal patterns show that the most intense MHWs occur between May and September, with events extending into late autumn and early winter under extreme warming. This study also reveals several novel insights. First, the Po River plume is identified as a key factor for the onset and decline of MHWs. Lower river discharges are associated with intense MHW onset, while higher discharges aid in heat dissipation during decline phases. As, air-sea heat fluxes are demonstrated to play a critical role in MHW onset along the plume, these findings suggest that MHWs are more likely to develop and persist under low Po River discharge conditions, when water clarity increases and solar radiation absorption is enhanced due to reduced suspended sediments and organic matter. Second, the study identifies a gap in MHW activity, potentially linked to the Eastern Mediterranean Transient, highlighting the influence of natural variability on MHW dynamics. However, no correlation is found with the Ionian-Adriatic Bimodal Oscillating System, suggesting the need for further research on oceanographic influences. Consequently, the PGW approach is found to effectively captures the thermodynamic changes influencing the MHWs in the Adriatic Sea despite potentially oversimplifying future MHW dynamics as it assumes stationarity in climate signals. Finally, these findings underscore the urgent need for adaptive strategies to mitigate the impacts of intensified MHWs on marine ecosystems and coastal communities, particularly in vulnerable nearshore areas. Future research should incorporate ensemble of high-resolution projections and assess additional climate stressors to provide a more comprehensive understanding of Adriatic MHWs under future warming.