Organisations involved

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

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:

Sf   =   ΣU>25(U-25)3

Results

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 200236.92 149775.37
2 Kyrill 18 Jan 200736.38 123459.43
3 Nov 84 23 Nov 198435.54 130058.36
4 Dec 93 8 Dec 199336.97 98049.52
5 13 Jan 93 13 Jan 199340.48 73448.70
6 Daria (Burns' Day Storm 25 Jan 199037.92 88148.05
7 Anatol 3 Dec 199939.86 74247.01
8 23 Jan 93 23 Jan 199336.54 88243.04
9 Vivian 26 Feb 199035.16 94040.86
10 Great storm of 87 (87J) 16 Oct 198739.53 62238.42
11 Oratia (Tora) 30 Oct 200038.45 64536.67
12 Erwin (Gudrun) 8 Jan 200539.22 59836.08
13 Nov 81 2 Nov 198136.01 68732.07
14 Jan 86 20 Jan 198631.86 92129.77
15 13 Jan 84 13 Jan 198433.75 71627.53
16 14 Jan 84 14 Jan 198434.71 64927.14
17 Oct 86 20 Oct 198635.80 58426.79
18 5 Jan 91 5 Jan 199138.52 44925.67
19 Wiebke 28 Feb 199032.24 75125.16
20 Nov 92 25 Nov 199239.07 41824.93
21 Klaus 24 Jan 200937.23 47224.36
22 Feb 83 1 Feb 198332.29 71824.16
23 Xynthia 27 Feb 201032.62 66623.11
24 Jan 02 28 Jan 200234.23 55122.10
25 Dec 11 16 Dec 201140.02 34221.91
26 Martin 27 Dec 199937.18 41521.33
27 Stephen 26 Dec 1998 39.53 31719.58
28 Ulli 3 Jan 201236.32 39719.02
29 8 Jan 91 8 Jan 199135.97 40718.94
30 Lothar 26 Dec 199936.72 38018.82
31 Nov 88 29 Nov 198830.84 62518.33
32 Nov 96 6 Nov 199636.19 38518.26
33 Jan 83 18 Jan 198334.53 43617.94
34 Gero 11 Jan 200539.13 29317.55
35 Feb 88 9 Feb 198835.79 38017.42
36 Jan 95 22 Jan 199536.33 35617.07
37 Oct 96 28 Oct 199635.87 36816.98
38 11 Feb 90 11 Feb 199031.90 51516.72
39 Mar 86 25 Mar 198630.77 56316.40
40 Feb 09 9 Feb 200931.54 51016.00
41 Feb 96 7 Feb 199633.66 41815.94
42 Herta 3 Feb 199033.16 43715.94
43 Mar 97 28 Mar 199731.22 52315.92
44 8 Feb 90 8 Feb 199035.02 37015.90
55 Lore 28 Jan 199431.60 43813.82
57 Yuma 24 Dec 199739.92 20513.04
62 Fanny 4 Jan 199834.60 29712.30
63 Emma 29 Feb 200825.12 76812.17
123 Xylia 28 Oct 199826.72 2955.63
309 Dagmar (Patrick) 26 Dec 201130.08 651.77


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