Characterization of the mean and extreme Mediterranean cyclones and their variability during the period 1500 BCE to 1850 CE

Extratropical cyclones are important meteorological phenomena in the Mediterranean and are essential for local water supplies, yet they also pose significant hazards for the region as a result of extreme precipitation or wind events. Although they have been extensively studied using global and regional climate models, their spatial and temporal variability in the Late Holocene is poorly understood. Here, we study a 3350-year climatological simulation that allows us to characterize Mediterranean cyclones better and provides a baseline for more accurately assessing the long-term effects of future climate change on Mediterranean cyclones. To analyse Mediterranean cyclone characteristics, we use a seamless transient simulation from 1500 BCE to 1850 CE produced by the Community Earth System Model (CESM) with a 6-hourly temporal and 1.9°×2.5° horizontal resolutions. We found that Mediterranean cyclones exhibit pronounced multi-decadal variability in the order of 5 % throughout the entire Late Holocene with respect to several cyclone-related properties. For the cyclone frequency, a weak statistical relationship is identified with the East Atlantic (EA), East Atlantic/Western Russia (EAWR), and Scandinavian (SCAN) modes of circulation. Composite analyses of the most extreme cyclones with respect to wind speed and precipitation indicate that cyclones in the central Mediterranean have the potential to grow more intense over their entire lifetime than cyclones in the eastern Mediterranean. This is especially true for extreme wind speed cyclones, implying that people in the central Mediterranean are potentially more exposed to hazards caused by extreme cyclones.