Extreme downpours could become summer staple if global warming continues

Researchers from the Met Office and Newcastle University have identified how climate change could result in heavier summer rainfall, which in turn could increase the risk of flash flooding.

The study used a state-of-the-art climate change model to provide evidence for the first time that hourly summer rainfall rates could increase.

While summers are expected to become drier overall by 2100, intense rainfall indicative of serious flash flooding could become several times more frequent.

The study, published in the Nature and Climate Change journal, said: “Short duration rain events are predicted to intensify during the summer months in the southern United Kingdom.

“This predicted increase means more events would exceed the Met Office and Environment Agency Flood Forecasting Centre guidance threshold for serious flash flooding.”

The report highlights how short bursts of heavy rainfall triggered flooding in the north Cornwall town of Boscastle nearly a decade ago, when the coastal community was brought to its knees as a result of a pocket of unseasonable summer weather.

Last July, a major clean up operation took place after a falsh flood in the Calder Valley. Properties in Todmorden, where the Environment Agency sounded flood sirens, were under a foot and a half of water. The town, and nearby Hebden Bridge, had hit the national headlines the year before after suffering major flooding.

The results from the study are the first step towards building a more complete picture of how UK rainfall may change as our climate warms, researchers said.

Professor Hayley Fowler, from Newcastle University’s School of Civil Engineering and Geosciences, said: “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.”

It is the first time researchers have examined climate models in such detail to simulate how extreme hourly rainfall might change over time.

Dr Lizzie Kendon, lead author of the research at the Met Office, said: “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.”