Correlations between extreme winds and flooding across Europe

For our first paper we have systematically investigated the relationships between national wind and flood damage metrics at all timescales ranging from daily to seasonal during the winter season. This work is completed using high resolution meteorological reanalysis and river flow datasets to explore the historical period (1980-present). As well as this, data from the UKCP18 climate projections at 12km resolution is used to understand historical sampling uncertainty, and the possible impacts of future climate change.

The correlation between national aggregate wind gusts and precipitation peaks at ~10 days over Great Britain; whereas, the correlation between national aggregate wind gusts and river flows peaks at ~3 weeks. Results show the historical correlation between wind and flood damage becomes weaker as the definition of the metrics become more impact focussed, and this is true across all timescales from daily to seasonal. When this historical analysis is extended across Europe we find the timescale of maximum correlation varies strongly between nations, which have different driving processes.

In a future climate co-occurrence of most extreme events becomes roughly threefold more frequent, reducing present day return periods from 16 to 5 years. These results are of key importance to the insurance industry who require actionable information based on both the meteorological hazards and on the exposure of their portfolios.

Learn More

Synoptic conditions conducive for compound wind-flood events in Great Britain in present and future climates

Extreme wind is the main driver of loss in North-West Europe, with flooding being the second-highest driver. These hazards are currently modelled independently, and it is unclear what the contribution of their co-occurrence is to loss. They are often associated with extra-tropical cyclones, with studies focusing on co-occurrence of extreme meteorological variables. However, there has not been a systematic assessment of the meteorological drivers of the co-occurring impacts of compound wind-flood events.

This study quantifies this using an established storm severity index (SSI) and recently developed flood severity index (FSI), applied to the UKCP18 12 km regional climate simulations, and a Great Britain (GB) focused hydrological model. The meteorological drivers are assessed using 30 weather types, which are designed to capture a broad spectrum of GB weather.

Daily extreme compound events (exceeding 99th percentile of both SSI and FSI) are generally associated with cyclonic weather patterns, often from the positive phase of the North Atlantic Oscillation (NAO+) and Northwesterly classifications. Extreme compound events happen in a larger variety of weather patterns in a future climate. The location of extreme precipitation events shifts southward towards regions of increased exposure. The risk of extreme compound events increases almost four-fold in the UKCP18 simulations (from 14 events in the historical period, to 55 events in the future period). It is also more likely for there to be multi-day compound events. At seasonal timescales years tend to be either flood-prone or wind-damage-prone.

In a future climate there is a larger proportion of years experiencing extreme seasonal SSI and FSI totals. This could lead to increases in reinsurance losses if not factored into current modelling.

Learn More

User Engagment

We are very keen to work with other academics, insurers or financial institutions that can make use of the results. Results of our first user-engagement workshop can be found here.

Wind/flood risk correlation explorer

Bank Underground Blog

In 2022 a sequence of storms (Dudley, Eunice and Franklin) inflicted a variety of hazards on the UK and across Northwest Europe, resulting in £2.5–4.2 billion in insured losses. They dramatically illustrate the potential risk of a ‘perfect storm’ involving correlated hazards that co-occur and combine to exacerbate the total impact. Recent scientific research reinforces the evidence that extreme winds and inland flooding systematically co-occur. By better modelling how this relationship might raise insurers’ capital risk we can more firmly argue that insurers’ model assumptions should account for key dependencies between perils. This will ensure that insurers continue to accurately assess and manage risks in line with their risk appetite, and that capital for solvency purposes remains appropriate.

Read the full blog here

Learning from CBES: Survey Report

The UK Centre for Greening Finance and Investment (UKCGFI) and the Climate Financial Risk Forum (CFRF) worked together over 2022 to gather and synthesise the lessons from the process of the Bank of England’s Climate Biennial Exploratory Scenario (CBES), both to capture the learning for UK FIs and to share this internationally. This paper focuses on the findings of the survey and brings in some initial perspectives from the analysis of interview findings. Information was gathered from 37 survey respondents, across 15 of the 18 CBES participants, and 12 interviews over an eight month period. The findings were validated at two workshops with CBES participants in January 2023.

Download the reports here

Learning from CBES: Reccomendations

This CGFI report outlines proposed recommendations for Central Banks and Supervisors, Financial Institutions, Government, Professional Bodies and Research and Technical Institutions that emerged from the CGFI study “Learning from the 2021/22 Climate Biennial Exploratory Scenario (CBES) Exercise”.

Download the reports here

Details of all CGFI CBES content here

What Next?

There are number of ongoing tasks within this project including:

  • Comparing the size of hazard vs. exposure unvcertainties for European wind storm risk.
  • Developing open source wind storm and flood catastrophe models.
Please get in touch if you're interested in talking about this work!