Future evolution of Marine Heatwaves in the Mediterranean Sea

Sofia Darmaraki,Vladimir Djurdjevic,Laurent Li,Leone Cavicchia,Florence Sevault,Samuel Somot,Gianmaria Sannino,William David Cabos Narvaez,Pierre Nabat,Dmitry V Sein

doi:10.1007/s00382-019-04661-z

Abstract

Extreme ocean warming events, known as marine heatwaves (MHWs), have been observed to perturb significantly marine ecosystems and fisheries around the world. Here, we propose a detection method for long-lasting and large-scale summer MHWs, using a local, climatological 99th percentile threshold, based on present-climate (1976–2005) daily SST. To assess their future evolution in the Mediterranean Sea we use, for the first time, a dedicated ensemble of fully-coupled Regional Climate System Models from the Med-CORDEX initiative and a multi-scenario approach. The models appear to simulate well MHW properties during historical period, despite biases in mean and extreme SST. In response to increasing greenhouse gas forcing, the events become stronger and more intense under RCP4.5 and RCP8.5 than RCP2.6. By 2100 and under RCP8.5, simulations project at least one long-lasting MHW every year, up to three months longer, about 4 times more intense and 42 times more severe than present-day events. They are expected to occur from June-October and to affect at peak the entire basin. Their evolution is found to occur mainly due to an increase in the mean SST, but increased daily SST variability also plays a noticeable role. Until the mid-21st century, MHW characteristics rise independently of the choice of the emission scenario, the influence of which becomes more evident by the end of the period. Further analysis reveals different climate change responses in certain configurations, more likely linked to their driving global climate model rather than to the individual model biases.

Highlights

Episodes of large-scale warm temperature anomalies in the ocean may prompt substantial disruptions to marine ecosystems (Frölicher and Laufkötter 2018; Hobday et al 2016) and major implications for fisheries as well (Mills et al 2013)
The aim of this study is to provide a robust assessment of the future evolution of summer marine heatwaves (MHWs) in the Mediterranean Sea using an ensemble of high-resolution coupled regional climate system models (RCSM), driven by GCMs and a multi-scenario approach (RCP2.6, RCP4.5, RCP8.5)
We examine the frequency of MHWs (Annual count of events), and the duration of each event is defined as the time between the first and last day for which a minimum of 20% of Mediterranean Sea surface is touched by a MHW

Summary

Introduction

Episodes of large-scale warm temperature anomalies in the ocean may prompt substantial disruptions to marine ecosystems (Frölicher and Laufkötter 2018; Hobday et al 2016) and major implications for fisheries as well (Mills et al 2013). Extended author information available on the last page of the article observational systems revealed adverse consequences emanating from them Their occurrence is likely to intensify under continued anthropogenic warming (Frölicher et al 2018; Oliver et al 2018a), engendering the need for a more comprehensive examination of their spatiotemporal distribution and underlying physical causes. In the Mediterranean area, a well-known“Hot Spot” region for climate change (Giorgi 2006), the annual mean basin SST by the end of the 21st century is expected to increase from + 1.5 °C to + 3 °C relative to present-day levels, depending on the greenhouse gas (GHG) emission scenario (Somot et al 2006; Mariotti et al 2015; Adloff et al 2015) This significant rise in SST is expected to accelerate future MHW occurrence, in congruence with projections for GHG-induced heat stress intensification of 200–500% throughout the region (Diffenbaugh et al 2007). The Mediterranean area’s sensitivity to increased GHG forcing is mainly attributed to a significant mean warming and increased interannual warm-season variability, along

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