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Introduction
European winter windstorms are a major cause of losses to the insurance sector. To help the sector better understand this risk the Operational Windstorm Service for the Insurance Sector has been developed. The development of the service follows from a Proof of Concept for a Sectorial Information Service to provide information about European windstorms, which is the Windstorm Information Service (WISC), part of the Copernicus Climate Change Service (C3S). This document describes the Tier 1 indicators and how they are produced by the University of Reading. The Tier 1 indicators provide summary statistics for wind storm activity per year and per European country.
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The choice of the thresholds is based on the work done for WISC. The Storm Severity Index is defined as:
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SSI$$SSI = A \ast [mean(Uu_{10m} > threshold)]^3^3$$ |
Where A is the area over land in km2 and 𝑢10𝑚 is 10m wind speed from the reanalysis data. This is equivalent to the SSI used in Dawkins et al., (2016).
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Table 1: Overview of key characteristics of the Tier 1 indicator dataset.Anchor table1 table1
Data Description | |
Dataset title | Tier 1 Indicators |
Data type | Summary statistics of European windstorms. |
Topic category | Natural risk zones, Atmospheric conditions |
Sector | Insurance |
Keyword | Number of cyclones, intensities. |
Dataset language | English |
Domain | Europe defined as follows:
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Horizontal resolution | Statistics derived from ERA5, ~30 km. |
Temporal coverage | 1979-10-01/to/2021-03-31 |
Temporal resolution | Annual, Decadal |
Vertical coverage | 10-m near surface |
Update frequency | No updates expected |
Version | 1.1 |
Model | ERA5 |
Experiment | N/A |
Provider | University of Reading (UREAD) |
Terms of Use | https://cds.climate.copernicus.eu/api/v2/terms/static/licence-to-use-copernicus-products.pdf |
Variable Description
The Tier 1 indicators, which are provided in Excel format, include the following fields:
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Table 2: Overview and description of variablesAnchor table2 table2
Variables | |||
Long Name | Short Name | Unit | Description |
Number of windstorms (vorticity) | No. storms | Number | Based on the storm tracks. A storm is said to pass through a region if a storm's track vorticity center passes through the region. These are provided per year and per decade. |
Number of windstorms (wind) | No. storms | Number | A storm is said to pass through the region if the land only 10m wind speed maximum (within 3° of the vorticity center) passes through the region. These are provided per year and per decade. |
Mean maximum 10m wind speed (u10m land only) (>0.0 m s-1) | Mean Wind | m s-1 | Mean maximum wind speed at 10m over land calculated for each study region directly from the reanalysis data. The threshold used here was 0.0 m s-1. These are provided per year. |
Number of extreme windstorms (u10m land only) (>15.6 m s-1) | No. storms (land > 15.6 m s-1) | Number | A storm is said to pass through the region if the land only 10m wind speed maximum (within 3° of the vorticity center) is greater than 15.6 m s-1 and passes through the region. This is the same threshold used for ERA-Interim in WISC. These are provided per year and per decade. |
Mean maximum wind speed (u10m land only) (>15.6 m s-1) | Mean Wind (land > 15.6 m s-1) | m s-1 | Calculated for each study region directly from the reanalysis data. The threshold used here was 15.6 m s-1. Maximum averaged over all storms. These are provided per year and per decade. |
Number of extreme windstorms, (u10m land only) (>20.0 m s-1) | No. storms (land > 20.0 m s-1) | Number | A storm is said to pass through the region if the land only 10m wind speed maximum (within 3° of the vorticity center) is greater than 20.0 m s-1 and passes through the region. These are provided per year and per decade. |
Mean maximum wind speed (u10m land only) (>20.0 m s-1) | Mean Wind (land > 20.0 m s-1) | m s-1 | Calculated for each study region directly from the reanalysis data. The threshold used here was 20.0 m s-1. Maximum averaged over all storms. These are provided per year and per decade. |
Number of extreme windstorms (u10m land only) (>25.0 m s-1) | No. storms (land > 25.0 m s-1) | Number | A storm is said to pass through the region if the land only 10m wind speed maximum (within 3° of the vorticity center) is greater than 25.0 m s-1 and passes through the region. These are provided per year and per decade. |
Mean maximum wind speed (u10m land only) (>25.0 m s-1) | Mean Wind (land > 25.0 m s-1) | m s-1 | Calculated for each study region directly from the reanalysis data. The threshold used here was 25.0 m s-1. Maximum averaged over all storms. These are provided per year and per decade. |
Mean severity of storms, per year and per decade, 20.0 m s-1 threshold. | SSI | None (Unitless SSI) | The severity of each storm was assessed using a Storm Severity Index (SSI). This metric was also calculated from the land masked wind speed of the re-analysis data. Wind threshold > 20.0 m s-1. These are provided per year and per decade. |
Mean severity of storms, per year and per decade, 25.0 m s-1 threshold. | SSI | None (Unitless SSI) | The severity of each storm was assessed using a Storm Severity Index (SSI). This metric was also calculated from the land masked wind speed of the re-analysis data. Wind threshold > 25.0 m s-1. These are provided per year and per decade. |
Input Data
The input data to the cyclone track and Tier 1 production is summarised in Table 3 and described below.
Table 3: Overview of climate model data for input to Operational Storm Track, summarizing the model properties and available scenario simulations.Anchor table3 table3
Input Data | ||||
Model name | Model centre | Scenario | Period | Resolution |
ERA5 | ECMWF | Reanalysis | 1979-2020 | ~30km |
Input Data 1
ERA5 Reanalysis
Data from the ECMWF ERA5 reanalysis (Hersbach et al, 2020) extracted directly from the mars archive for the period 1979-2020 at 3 hourly intervals for the seasonal period of October to March when the majority of European windstorms occur. The 850hPa relative vorticity is spectrally filtered prior to applying the tracking algorithm. Full resolution MSLP, 925hPa winds and 10m winds are also added to the cyclone tracks.
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This is calculated by applying a regional mask and then a wind speed threshold mask to the ERA5 10m winds. For the resulting wind speeds the maximum is taken and average per season computed. This gives an indication of the highest land-only 10m wind speed which could be experienced in a country.
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Storm Severity Index (SSI) is defined as:
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SSI$$SSI = A \ast [mean(Uu_{10m} > threshold)]^3^3$$ |
Where A is the area over land in km2 and 𝑢10𝑚 is 10m wind speed calculated from the re-analysis data. This is equivalent to a definition of SSI used in Dawkins et al., (2016), with the only difference being the threshold of 10m wind speed used. This metric is also calculated from the land masked, and the ERA5 masked wind speeds.
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M. A., Thornton, H. E., and Youngman, B. D. (2014) The XWS open access catalogue of extreme European windstorms from 1979 to 2012, Nat. Hazards Earth Syst. Sci., 14, 2487-2501
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This document has been produced in the context of the Copernicus Climate Change Service (C3S). The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreementAgreement signed on 11/11/2014 and Contribution Agreement signed on 22/07/2021). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose. The users thereof use the information at their sole risk and liability. For the avoidance of all doubt , the European Commission and the European Centre for Medium - Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view. |
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