European Windstorms in a Changing Climate: Storm Tracks, Clustering and Multi-peril Extremes
David STEPHENSON, Principal Investigator
Support by the AXA Research Fund
TYPE OF SUPPORT
Calls for Projects
Tracking future windstorms in Europe
Large annual losses triggered by European windstorms can arise from collective risk caused by the clustering of successive storms and the dependency between storm-related wind speed and rainfall extremes. There is growing scientific evidence that natural variations in the large-scale flow induce dependency between successive storms and between wind and rainfall extremes. “For example, the severe storms that impacted France in December 1999 were due to the persistence of a strong upper level jet stream. We know that this condition provides the energy needed for explosive growth of damaging windstorms”, says Pr. David Stephenson.
Pr. David Stephenson leads a project aimed at quantifying future changes in collective risk due to European windstorms. He assesses in particular the potential evolution in European windstorm events focusing on large scale changes in the North Atlantic storm track and their relation with regional changes in landfall windstorms over Europe, extreme wind speeds and precipitation associated and their relationship with wind damage and floods as well as clustering of extremes related to windstorms landfalls over Europe.
He collaborates with the UK Met Office to statistically analyze this storm tracks from a set of state-of-the-art high resolution regional climate model projections for the 21st century. This will allow better quantifying trends and clustering in future European windstorms. He will then look at dependency between successive storms and between extreme winds speeds and extreme precipitation. In addition, this project will set up a European windstorms research network to help bring together critical mass in this important area of climate science.
The global modeling results may enable an analysis of the large-scale driving factors of European windstorms under a changing climate, while the European regional modeling runs will give an understanding of the hazard produced by storms. These more dynamic predictions are of high relevance to the insurance sector as they allow to look at the changing rates of hazards.
Professor David Stephenson is an internationally renowned expert of the statistical analysis of weather and climate. He has developped advanced methodologies that provide deeper understanding of climate variations and improve the quality of forecasts. Since 1998, he has worked with catastrophe modellers in the global reinsurance industry. In 2006, he was also a key founding member of the Willis Research Network, the world’s largest partnership between academia and insurance companies. Professor Stephenson has received Axa funding for his RACEWIN project, which will assess the impact of climate change on European windstorms.
Climate change is a vast area of research. But how precise can mathematical projections be?
We can now make adaptive forecasting of climate change. And instead of just saying “by the end of the XXIe Century, it will be 5 degrees warmer”, we are now trying to make predictions for the next year or the next ten years. It is important for the insurance sector because it allows us to look at the changing rate of hazards. Historical catastrophe models assume that the risk is stationary, but we know that weather events and their rates do change in time. So our predictions get more dynamic.
What do we know of the impact of climate change on storms in Europe?
I'm one of the lead authors for the chapter on “Regional Climate and Extremes” in the next Intergovernmental Panel on Climate Change (IPCC) report. One of our problems today is making statements on that more local scale for the future. Today, the different models get very different answers.
To what extent can we really predict a storm today ?
There is some predictability of the strong wind patterns in the atmosphere at least a month ahead, a couple of months maximum. We can say whether there is a higher risk of having storms, but we cannot predict exactly where it is going to happen or how many storms there will be. For example, the severe storms that impacted France in December 1999 were due to the persistence of a strong upper level jet stream. We know that this condition provides the energy needed for explosive growth of damaging windstorms. But we could not go further. It is a probabilistic prediction.
Your RACEWIN project aims at improving these projections. How will you proceed ?
Starting in October, we will collaborate with the UK Met Office to statistically analyse the storm tracks (which trace the central pressure of a storm all along its way) from a set of high-resolution regional climate model projections for the 21st century. This will allow us to better quantify trends and clustering in future European windstorms. Clustering measures the tendency of storms to occur together over a short time in a particular region, rather than being randomly distributed. We will look at the dependency between successive storms and between extreme wind speeds and extreme precipitation. In addition, our project will set up a European windstorms research network to help bring together critical mass in this important area of climate science.
* Note : the IPPC is a scientific intergovernmental body of the United Nations, in charge of assessing the risks of climate change. Its fifth report, a reference document, is due in 2014.
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