Quantifying the relationship between co-occurring flood and wind damage over North-West Europe, in a present and future climate.

Strong winds and extremes in precipitation are capable of producing devastating socio-economic impacts across Europe. Although it is well known that individually these drivers cause billions of Euros of damage, their combined impacts are less well understood. Previous work has either focused on daily or seasonal timescales, demonstrating that compound wind and precipitation events are commonly associated with passing cyclones or particularly wet and windy years respectively. This study showcases a range of ongoing results from the UK Centre from Greening Finance and Investment relevant to the topic.

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.