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Will hurricanes or storms be more severe in the future?

Severe storms and hurricanes are some of the most devastating and costly consequences of climate.

In the Walker Institute we have unique expertise in climate and weather and the interface between the two. We seek to improve predictions of extreme events like storms and hurricanes by advancing our knowledge of storm processes and developing more detailed climate models.

We work with the user community to make our research more effective – e.g., the insurance industry.

Recent extreme events

Why was autumn 2000 the wettest in the UK for several centuries and are we likely to have more floods in coming years?

What caused the extreme heat in southern Europe during August 2003, and are such events more likely in the future?

Low pressure systems (depressions or mid-latitude cyclones) track across the Atlantic every few days and dominate the weather over Europe.  They sometimes bring with them high winds or heavy rainfall that can cause flooding.  In the summer, depressions can bring much needed rain following a spell of dry weather. These low pressure systems tend to follow similar paths across the Atlantic, along what is known as the North Atlantic storm track.

The paths of these storms can sometimes be deflected by a persistent high pressure area that acts as a “block”. A block over Europe can last for several weeks and can bring bitter cold in winter or extreme heat and drought in summer.  The severe winter of 1963 was the result of a persistent block over the UK (the blue area in the figure).

Could Europe experience more severe storms or flooding in the future?

If we are to answer this question we must understand how the number of storms, their intensity, and the position of the Atlantic storm track might  be affected by climate variability or change.

We seek to improve our understanding of storm processes and the complex interaction between storm tracks and blocking – something that is still a challenge for modern weather forecasting and climate models.

We are also investigating the relationship between the storm track and larger scale natural variations in climate.  For example, the North Atlantic Oscillation (NAO) – a difference in pressure between Iceland and the Azores.  When pressure is high over Iceland the storm track is further south – bringing more storms and hence rain and wind to southern parts of Europe. The NAO varies naturally and may be affected by climate change. There is still much to understand about the NAO and its relationship to the North Atlantic storm track - both in today’s climate and in the future.

We are using higher resolution models (which can represent smaller scale processes) to investigate how the the representation of storm tracks and blocking improves (for example see HiGEM website.)

How will a weaker thermohaline circulation affect storms over Europe?

In most climate models the thermohaline circulation (a large scale overturning circulation in the ocean) weakens as greenhouse gases become more abundant in the atmosphere. This has a big effect on the temperature of the sea surface in the North Atlantic. At present, very little is know about how such changes would affect the storm track. 

Idealised experiments that impose rather crude changes in sea surface temperture, suggest that a weaker thermohaline circulation broadens the storm track and shifts it southwards.

Email: walker_info@reading.ac.uk Tel: +44(0)118 378 7380 Copyright © 2006 Walker Institute. All rights reserved.