Selecting the storms
Fifty of the most extreme storms of the 5730 that passed through the region 15°W-25°E, 35°N-70°N in the period 1979-2013 have been selected for the XWS catalogue. The challenge when selecting these storms was defining an `extreme storm'. A storm can be defined as extreme in many ways, for example in terms of a meteorological index, or extreme values of insured losses.
Insurance loss storms
An initial list of insurance loss storms (hereafter `insurance storms' ) was compiled after consultation with Willis Research Network, containing 22 storms that had caused large insurance losses. Of these 22, only one (Capella, January 1976) was not in the period covered by ERA-Interim and was therefore excluded from the list. In addition to these 21 events, a further 2 events, which were known to have caused significant damage and were well researched, were included as being typical of the type of event that we wished to capture in the catalogue.
There were numerous other events that were considered, e.g. polar lows and other named storms, however they were not included due to either not causing damage over Europe (the polar lows) or due to there being very little information on them. The final list included 23 'insurance' events; these are the named storms in the table below, as opposed to storms identified by dates (e.g. Nov 84).
The aim for this catalogue was to find an optimal meteorological index that could capture the high insurance loss storms (by ranking them highly), and identify other similar events that were not recorded as high loss. These other storms may not have recorded high insurance losses either because they missed large urban areas, or because of incomplete loss data records.
Meteorological indices from both the track and footprint of the storm were investigated. These indices included the maximum wind speed of the storm (Umax), defined as the maximum 925hPa wind speed (from ERA-Interim) over the Continental European land mass within a 3° radius of the cyclone track. Radii of 6° and 10° were considered, both resulting in a slightly poorer performance by the index (i.e. the insurance storms tended to be ranked lower when ranked by this index).
The size of the storm (N) was also considered, defined as the number of footprint grid points over European and Scandinavian land for which the maximum gust exceeds 25ms-1, which is proportional to the land area exceeding this threshold. A threshold of 25ms-1 was used as it is recognised as being the wind speed at which damage starts to occur. The use of a relative local 98th percentile threshold, as used by Klawa & Ulbrich (2003), was also considered. This resulted in the selection of relatively weak, small scale Mediterranean storms (`medicanes') which are not well represented in the re-analysis data.
Indices Umax and N can be combined to form a storm severity index (SSI). The SSIs tested were (i) Sft, derived by combining the track index (Umax)3 (intensity) and footprint index N (size):
Sft = (Umax)3 N,
and (ii), Sf, which is estimated only from the footprint data, defined as the sum of the excess gust speed cubed at grid points over European and Scandinavian land:
The index Sft was found to be the most successful index at identifying the insurance loss storms, i.e. when ranking storms by this index, the insurance loss storms ranked higher compared to the other indices. This index depends on both the area and maximum wind speed intensity of the storm. The index Sft selects storms located over the UK and Northern Europe and samples storms over the full time period of the XWS catalogue hence giving a good representation of the meteorologically extreme and severe Atlantic storms that occurred throughout the period. For these reasons we have chosen to use Sft to select the 50 storms for the XWS catalogue.
A more detailed discussion of the results will be given in the forthcoming paper (link to come).
Table showing the meteorological index values for the 50 storms selected for the XWS catalogue
|Rank in Sft||Name||Date of Umax||Umax (ms-1)||N||Sft(x106)|
|1||Jeanette||27 Oct 2002||36.92||1497||75.37|
|2||Kyrill||18 Jan 2007||36.38||1234||59.43|
|3||Nov 84||23 Nov 1984||35.54||1300||58.36|
|4||Dec 93||8 Dec 1993||36.97||980||49.52|
|5||13 Jan 93||13 Jan 1993||40.48||734||48.70|
|6||Daria (Burns' Day Storm||25 Jan 1990||37.92||881||48.05|
|7||Anatol||3 Dec 1999||39.86||742||47.01|
|8||23 Jan 93||23 Jan 1993||36.54||882||43.04|
|9||Vivian||26 Feb 1990||35.16||940||40.86|
|10||Great storm of 87 (87J)||16 Oct 1987||39.53||622||38.42|
|11||Oratia (Tora)||30 Oct 2000||38.45||645||36.67|
|12||Erwin (Gudrun)||8 Jan 2005||39.22||598||36.08|
|13||Nov 81||2 Nov 1981||36.01||687||32.07|
|14||Jan 86||20 Jan 1986||31.86||921||29.77|
|15||13 Jan 84||13 Jan 1984||33.75||716||27.53|
|16||14 Jan 84||14 Jan 1984||34.71||649||27.14|
|17||Oct 86||20 Oct 1986||35.80||584||26.79|
|18||5 Jan 91||5 Jan 1991||38.52||449||25.67|
|19||Wiebke||28 Feb 1990||32.24||751||25.16|
|20||Nov 92||25 Nov 1992||39.07||418||24.93|
|21||Klaus||24 Jan 2009||37.23||472||24.36|
|22||Feb 83||1 Feb 1983||32.29||718||24.16|
|23||Xynthia||27 Feb 2010||32.62||666||23.11|
|24||Jan 02||28 Jan 2002||34.23||551||22.10|
|25||Dec 11||16 Dec 2011||40.02||342||21.91|
|26||Martin||27 Dec 1999||37.18||415||21.33|
|27||Stephen||26 Dec 1998||39.53||317||19.58|
|28||Ulli||3 Jan 2012||36.32||397||19.02|
|29||8 Jan 91||8 Jan 1991||35.97||407||18.94|
|30||Lothar||26 Dec 1999||36.72||380||18.82|
|31||Nov 88||29 Nov 1988||30.84||625||18.33|
|32||Nov 96||6 Nov 1996||36.19||385||18.26|
|33||Jan 83||18 Jan 1983||34.53||436||17.94|
|34||Gero||11 Jan 2005||39.13||293||17.55|
|35||Feb 88||9 Feb 1988||35.79||380||17.42|
|36||Jan 95||22 Jan 1995||36.33||356||17.07|
|37||Oct 96||28 Oct 1996||35.87||368||16.98|
|38||11 Feb 90||11 Feb 1990||31.90||515||16.72|
|39||Mar 86||25 Mar 1986||30.77||563||16.40|
|40||Feb 09||9 Feb 2009||31.54||510||16.00|
|41||Feb 96||7 Feb 1996||33.66||418||15.94|
|42||Herta||3 Feb 1990||33.16||437||15.94|
|43||Mar 97||28 Mar 1997||31.22||523||15.92|
|44||8 Feb 90||8 Feb 1990||35.02||370||15.90|
|55||Lore||28 Jan 1994||31.60||438||13.82|
|57||Yuma||24 Dec 1997||39.92||205||13.04|
|62||Fanny||4 Jan 1998||34.60||297||12.30|
|63||Emma||29 Feb 2008||25.12||768||12.17|
|123||Xylia||28 Oct 1998||26.72||295||5.63|
|309||Dagmar (Patrick)||26 Dec 2011||30.08||65||1.77|