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‘Perfect storm’ coastal flood potential multiplied by climate change – University of Reading

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‘Perfect storm’ coastal flood potential multiplied by climate change

Release Date 18 September 2019

Compound Flooding

Some of the European coasts and river estuaries may be at even greater risk of flooding due to climate change than previously thought, a new study has found.

A team led by the University of Reading and University of Graz carried out the first ever analysis of how a combination of sea level rise and increased rainfall in a future climate could cause extreme flooding in some low-lying coastal areas and near river mouths.   

Previous studies about future coastal flooding have mainly considered these hazards in isolation, but the new study argues that future floods in these areas could be even worse than expected, increasing the scale of the task of protecting people and buildings in them.

Dr Emanuele Bevacqua, lead author of the latest study, published today in the journal Science Advances, said: “Current flood risk assessment usually only considers one hazard at a time, ignoring how multiple conditions might combine to exacerbate the impact. This approach is one-dimensional and risks underestimating the severity of future flooding in some areas, putting lives in danger.

“Interaction between different hazards, such as storm surges, heavy rain and wet soils, has the potential to create a ‘perfect storm’ for big floods, with potentially dire consequences if people are not sufficiently prepared.”

Currently, flood risk is usually calculated based on storm surges and extreme rainfall separately. While this works in some areas, it is unreliable in coastal stretches and around river mouths where both these hazards often interact to cause more severe ‘compound flooding’.

This type of flooding was experienced in Lymington in the UK in 1999, and the Ravenna in Italy in 2015. In 2012, precautionary evacuations were also carried out in the northern Netherlands after the Noorderzijlvest water board was threatened by compound flooding.

The new study shows the potential for compound flooding will not be only increased by sea level rise, but will additionally be affected by changes in extreme storm surges and rainfall. The compound flooding potential will increase in northern Europe also due to increasing rainfall intensities, consistent with a future warmer atmosphere that allows storms to carry more moisture.

The scientists behind the flooding research are calling for coastal adaptation planning, which currently focuses predominantly on sea level and rainfall changes separately, to incorporate the interaction between multiple hazards when necessary. This would lead to more robust plans to prepare for big floods.

The latest study follows another by some of the same scientists, led by those at University of Birmingham, which assessed changes in long, dry periods that coincide with extremely high temperatures in Europe. An example of such an event includes the 2018 summer event that brought water shortages and wildfires to much of Northern Europe.

The research demonstrated how such events have become more frequent across Europe over the period 1950-2013 due to increasing temperatures. The authors state that this increase is likely to continue in the future due to climate change, causing drought conditions to set in faster and become more severe when such events occur. This may lead to an increased risk of wildfires and reduced crop yields.

Dr Bevacqua said: “Identifying European regions potentially facing compound flooding in a warmer climate, our study provides a basis for follow-up detailed local compound flooding risk assessments and adaptation planning.

“If we continue to base our adaptation plans on single hazards, such as extreme storm surges or rainfall, we may not be prepared for some of the extreme events we are likely to see in the future due to climate change.”

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