Climate change, impacts and vulnerability in Europe ... - MemoFin.fr

Changes in the climate systemclosely associated with atmospheric fronts whichdelineate changes in temperature, moisture, windspeed and direction, and atmospheric pressure. Innorthern and north-western Europe severe cyclonescan occur all year. In central Europe severe cyclonesoccur mainly between November and Februarywhereas weaker cyclones can also occur in otherseasons.north‐western European during the 1880s, followedby below average conditions between the 1930s and1960s, a pronounced increase in storminess until themid-1990s, and average or below activity afterwards.Somewhat similar patterns were observed in otherparts of Europe.Studies of storm activity have increased in recentyears as a result of improved observationaldatasets and the development of algorithms for theidentification and quantification of these phenomena(Ulbrich et al., 2009). In addition, high-resolutionGCM simulations for both present-day climateand climate change scenarios are increasinglybecoming available (van der Linden and Mitchell,2009). Nevertheless, there are still considerableuncertainties in our understanding of the processesinfluencing current storm activity and how thesemay be affected by climate change (Bengtsson et al.,2006; Pinto et al., 2007; Ulbrich et al., 2009).Storm events are associated with intense winds andprecipitation, which may lead to structural damage,flooding and storm surges (see Section 3.2.3 andChapter 5). These events can have large impacts onhuman health and on vulnerable systems, such asforests, and transport and energy infrastructures.According to the Munich Re NatCatSERVICE andthe EM-DAT database, storms were the costliestnatural hazard (in terms of insured losses) in Europebetween 1998 and 2009; they ranked fourth in termsof the number of human casualties (EEA, 2011b).Map 2.966 o60 o54 o48 o42 oTrends in the extreme windspeeds in the period 1871–2008based on reanalysisPast trendsStudies of past changes in extra-tropical storms haveused a variety of methods for analysing their activityin the storm track regions, making it difficult tocompare the results of different studies or to assessif there is any underlying climate change signal(Meehl et al., 2007; Ulbrich et al., 2009; Wang et al.,2011). Storm location and intensity in Europe hasshown considerable variation over the past century.Locally, increases in maximum gust wind speedshave been observed over recent decades (Usbecket al., 2010) but there is evidence for decreases instorm frequency since the 1990s (Ulbrich et al.,2009). Wind data at the local or regional levels canshow a series of decreases and increases continuingover several decades. Long records of wind speedfor various regions across Europe indicate thatstorminess has not significantly changed overthe past 200 years (Matulla et al., 2007). They alsoindicate relatively high levels of storminess in36 o 8 o W 0 o E 8 o 16 o 24 oTrends in the annual 95th percentile of daily maximumwind speeds, 1871–2008Note:Wind speed (m/s) α = 0.05– 0.2 – 0.15 – 0.1 – 0.05 0 0.05 0.1 0.15 0.2Gale day trends> 0.075 > 0.070 > 0.065 > 0.060 > 0.055Trends in the annual 95th percentile of daily maximumwind speeds in the 20th century reanalysis data set(ensemble mean) during the period 1871–2008.The trend is given in the units of the interannualstandard deviation and plotted only when significant.The coloured circles indicate trends in the number of'gale days' (an index that represents the number ofextremely windy days) over the period at the specificlocations.Source: Donat, Renggli, et al., 2011.Climate change, impacts and vulnerability in Europe 201271