Summer floods to become more frequent
Summer downpours and flash flooding are expected to become far more frequent across South England and Wales according to new research by the Exeter based Met Office and Newcastle University.
The study, published in the Nature Climate Change, used a high-resolution model to predict the effects that climate change would have on UK’s summer floods.
They found that, in a worst case scenario hourly summer rainfall could become five times more frequent by the end of the century, which would hugely increase the chance of ‘flash floods.’
Dr Lizzie Kendon, lead author of the study from the Met Office, said, “Until now, climate models haven’t been able to simulate how extreme hourly rainfall might change in future. The very high-resolution model used in this study allows us to examine these changes for the first time.
“It shows heavier summer downpours in the future, with almost five times more events exceeding 28mm in one hour in the future than in the current climate – changes we might expect theoretically as the world warms.
“However, we need to be careful as the result is only based on one model – so we need to wait for other centres to run similarly detailed simulations to see whether their results support these findings.”
Summer floods, like those that occurred in 2012, are usually quick but intense and much harder to predict than their winter equivalents. They can have disastrous effects on agriculture and tourism.
Prof Hayley Fowler from Newcastle University added, “We need to understand about possible changes to summer and winter rainfall so we can make informed decisions about how to manage these very different flooding risks in the future.
“The changes we have found are consistent with increases we would expect in extreme rainfall with increasing temperatures and will mean more flash floods”.
The research itself marks a breakthrough in prediction models due to the difficulty of predicting summer rainfall trends compared to winter trends.
This is because in winter it is the daily or multi-day rainfall totals that are important, because we tend to get steady, long-lasting periods of rain from large scale weather systems – similar to those seen during the winter floods of 2013/14.
In summer, however, it is the hourly rates that are more important as rain tends to fall in short but intense bursts – as seen during the Boscastle flooding of 2004 and ‘Toon Flood’, otherwise known as Thunder Thursday, in Newcastle in 2012.
Climate models have so far lacked the detail to accurately simulate the smaller-scale storms which cause this type of rain.
To deal with this issue, this study uses a climate model with a higher level of detail (resolution) than ever used before to examine future rainfall change.
This model gives a realistic representation of hourly rainfall, allowing us to make future projections with some confidence.
It was so computer intensive that only the southern half of the UK could be studied and even then it took the Met Office supercomputer – one of the most powerful in the world – about nine months to run the simulations.
These simulations looked at two 13-year periods, one based on current climate and one based on expected climate around 2100.
Professor Fowler adds: "The next steps are to see if these changes are consistent with observed trends in summer rainfall extremes and changes projected by climate models in other parts of the world. We will be looking at this over the next five years, jointly with the Met Office and other leading international scientists in the European Research Council funded INTENSE project.”
