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

Abstract. Extratropical cyclones are important meteorological phenomena in the Mediterranean and 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 variability in the late Holocene is poorly understood. Here, we study a 3350-year climatological simulation that allows us to characterise 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 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. For the cyclone frequency, a relationship is identified with the East-Atlantic, the East-Atlantic Western-Russia, and the Scandinavian modes of circulation. Cyclone frequency shows, although small, a significant increase in the eastern Mediterranean after severe volcanic eruptions with the highest sulphur injections. The composites 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 cyclones with extreme wind speed, implying that people in the central Mediterranean are potentially more exposed to hazards caused by extreme cyclones.