Extratropical cyclone statistics during the last millennium and the 21st century

Abstract

Abstract. Extratropical cyclones in winter and their characteristics are investigated in depth for the Atlantic European region, as they are responsible for a significant part of the rainfall and extreme wind and/or precipitation-induced hazards. Here, we use a seamless transient simulation with a state-of-the-art fully-coupled Earth System Model from 850 to 2100 CE as basis for the analysis. The RCP8.5 scenario is applied in the 21st century. During the Common Era, cyclone characteristics show pronounced variations on interannual and decadal time scales, but no external forcing imprint is found prior to 1850. Thus, variations of extratropical cyclone characteristics are mainly caused by internal variability of the coupled climate system. When anthropogenic forcing becomes dominant in the 20th century, a decrease of the cyclone occurrences mainly over the Mediterranean and a strong increase of extreme cyclone-related precipitation become detectable. The latter is due to thermodynamics as it follows the Clausius-Clapeyron relation. An important finding, though, is that the relation between temperature and extreme cyclone-related precipitation is not always controlled by the Clausius-Clapeyron relation, which suggests that dynamical processes can play an important role in generating extreme cyclone-related precipitation – for example in the absence of anomalously warm background conditions. Thus, the importance of dynamical processes, even on decadal time scales, might explain the conundrum that proxy records suggest enhanced occurrence of precipitation extremes during rather cold periods in the past.

Serial clustering of extratropical cyclones: a review of where, when and why it occurs

“…However, it is of crucial importance to assess how different cyclone clustering is for long and short aggregation time periods, and if clustering must be distinguished between different timescales. For example, only a few studies have linked slow oscillations in cyclone activity to ocean variability 93 or internal variability of the climate system 54 . On shorter aggregation timescales, more analysis of clustering on daily-weekly timescales is required to answer questions regarding the onset and end of cyclone families forming along the same frontal feature.…”

“…Several studies have also analysed clustering on decadal to multi-decadal timescales 52,53 . Some studies relate years with above (below) average storm activity to teleconnection patterns like the NAO 45,54 . Note that longer clustering periods, such as a season or a full year, typically consist of multiple cyclones that are unrelated to each other, thus not fulfilling the criteria of a cyclone family (see section 'Secondary cyclogenesis and cyclone families').…”

A ranking of concurrent precipitation and wind events for the Iberian Peninsula

“…(2012) provided evidence that the projected increase of windstorm‐related losses for the XXI century in Europe can be largely attributed to changes in the meteorological severity of the events. Other studies suggest that even if the total number of extratropical cyclones remains stable, the number of extreme cyclones affecting Western Europe in the future may slightly increase in association with an intensified polar jet extended towards Europe (e.g., Pinto et al ., 2009; Ulbrich et al ., 2009; Raible et al ., 2018; Catto et al ., 2019). For these reasons, shorter return periods for extreme windstorms and associated losses are estimated for most of Europe (Della‐Marta and Pinto, 2009; Donat et al ., 2011; Karremann et al ., 2014).…”

Historical predictability of rainfall erosivity: a reconstruction for monitoring extremes over Northern Italy (1500–2019)

“…The way how in the past decades Mediterranean cyclones have been producing trends of rainfall extremes remains elusive 93 , with significant negative trends of cyclone frequency in spring often compensated by positive trends in summer 94 . Raible et al 95 supports an increase of extreme cyclone-related precipitation, purely thermodynamically driven by the temperature increase and the Clausius-Clapeyron relation 96 . An intensification of geohydrological hazard owing to an increased occurrence of severe rain events during the past three to five decades is acknowledged for north-western Italy 97 and inner hilly areas of central Italy 98 .…”