Analysis of frequency and intensity of European winter storm events from a multi-model perspective, at synoptic and regional scales

Abstract

This study focuses on the analysis of winter (October-November-December-JanuaryFebruary-March; ONDJFM) storm events and their changes due to increased anthropogenic greenhouse gas concentrations over Europe. In order to assess uncertainties that are due to model formulation, 4 regional climate models (RCMs) with 5 high resolution experiments, and 4 global general circulation models (GCMs) are considered. Firstly, cyclone systems as synoptic scale processes in winter are investigated, as they are a principal cause of the occurrence of extreme, damage-causing wind speeds. This is achieved by use of an objective cyclone identification and tracking algorithm applied to GCMs. Secondly, changes in extreme near-surface wind speeds are analysed. Based on percentile thresholds, the studied extreme wind speed indices allow a consistent analysis over Europe that takes systematic deviations of the models into account. Relative changes in both intensity and frequency of extreme winds and their related uncertainties are assessed and related to changing patterns of extreme cyclones. A common feature of all investigated GCMs is a reduced track density over central Europe under climate change conditions, if all systems are considered. If only extreme (i.e. the strongest 5%) cyclones are taken into account, an increasing cyclone activity for western parts of central Europe is apparent; however, the climate change signal reveals a reduced spatial coherency when compared to all systems, which exposes partially contrary results. With respect to extreme wind speeds, significant positive changes in intensity and frequency are obtained over at least 3 and 20% of the European domain under study (35-72°N and 15°W-43°E), respectively. Location and extension of the affected areas (up to 60 and 50% of the domain for intensity and frequency, respectively), as well as levels of changes (up to +15 and + 200% for intensity and frequency, respectively) are shown to be highly dependent on the driving GCM, whereas differences between RCMs when driven by the same GCM are relatively small.

Assessment of extreme wind speeds from Regional Climate Models – Part 1: Estimation of return values and their evaluation

“…However, statistics reveal a systematic underestimation of simulated gusts by 10 to 30% for a 10-year RP, depending on location and height of terrain. Similar trends were found by Leckebusch et al (2006), who evaluated different RCM results from the EU project PRUDENCE with respect of the upper tail of the distribution function. However, and to our best knowledge, no evaluation of RCM gust speeds described by extreme value statistics has been conducted so far.…”

“…Several recent studies (e.g. Leckebusch et al, 2006;Pinto et al, 2006;Rockel and Woth, 2007;Pinto et al, 2007b) investigate the relation between the frequency and intensity of cyclones or extreme winds on the basis of global or regional climate models (GCM/RCM). They all found evidence of a slight increase in the frequency of high wind speeds over Europe, in particular at the end of the 21th century, compared to present climate conditions.…”

“…They all found evidence of a slight increase in the frequency of high wind speeds over Europe, in particular at the end of the 21th century, compared to present climate conditions. The studies consider either changes in the number of events over a specific threshold (>Bf 8; Rockel and Woth, 2007) or in the 98th percentiles of the distribution function (Leckebusch et al, 2006;Pinto et al, 2007a;Fink et al, 2009). Using such comparatively low thresholds, severe winter storms with high return periods (RP) or -the inverse -low probabilities are not adequately described.…”

Recent Change—Atmosphere

“…Early publications, for example, by Tinz (1996), Chen and Hellström (1999), Koslowski and Glaser (1999), Jevrejeva (2001), Omstedt and Chen (2001) and Andersson (2002) agreed that there has been a north-eastward shift in low-pressure tracks, which is consistent with a more zonal circulation over the Baltic Sea basin and the observed trend of a more positive NAO index, at least up to the 1990s (Trenberth et al 2007). A northward shift in low-pressure tracks is also consistent with model projections of anthropogenic climate change, as pointed out by Leckebusch and Ulbrich (2004), Bengtsson et al (2006), Leckebusch et al (2006), Pinto et al (2007) and, more recently, Lehmann et al (2011). Jacobeit et al (2001Jacobeit et al ( , 2003 and Hurrell and Folland (2002) discussed the strong temporal variability in the relationship between the general circulation of the atmosphere and surface climate characteristics over the past 300 years.…”

Ensemble prediction of coastal flood risk arising from overtopping by linking meteorological, ocean, coastal and surf zone models

“…The October 2004 storm discussed here was a significant event for the southern region of the UK. It has been postulated that the return period for extreme wind speeds may be reduced in future climates (Leckebusch et al, 2006;Pinto et al, 2007;Ulbrich et al, 2009), making this type of event more likely to occur. Coastal flood defences in the UK have typically been designed to withstand storm events with a return period of 50-100 years, and may therefore be inadequate in the future as the magnitude of storms with this return period increases.…”