Marine heat waves: Characterizing a major climate impact in the Mediterranean

The Mediterranean Sea has suffered accelerated warming in the last 40 years, bringing higher temperatures mainly in the extended summer season. Sea surface temperature (SST) is not only experiencing higher extremes but also persistent high values. In this context, marine heat waves (MHW), considered as persistent and spatially extensive SST anomalies, have emerged as a key global change-induced high impact on the oceans. Hence, the characterization and trend analysis of MHWs has become of major interest. In this work MHWs in a relatively small, but complex, basin such as the Mediterranean, have been characterized and long-term trends assessed from SST satellite data analysis. In this study, a minimum area threshold, 5 % of the area basin, has been applied to avoid heat spikes or small-scale events. A trend to more frequent, intense, and longer MHWs is found in the 1982–2021 period in the Mediterranean. In the analysis, regional differences were apparent in MHWs characteristics and trends across the different sub-basins evidencing the fact that, even in a relatively small basin such as the Mediterranean, it is necessary to include a spatial perspective in the MHW analysis. Regarding the characterization of MHWs and trend analysis in the Mediterranean, a growing trend has been found in terms of frequency, duration, and intensity that accelerated since 2000 and especially in the last decade. This indicates not only the intensification and higher frequency of MHWs but the emergence of a new type of more intense, long-lasting and spatially extensive MHWs in recent years.