Thunderstorm: Flash flooding could occur if heavy rain follows a heatwave, professor warns


A university professor has warned that people should “be careful” not to wish for heavy rain to cool temperatures because a downpour could lead to flash floods.

Rob Thompson, who is part of the University of Reading’s meteorology department, posted a video of an experiment on Twitter which used three glasses of water on different grass surfaces to demonstrate what happens when it rains after a drought.

In the first experiment, a glass of water is placed on damp grass and soaks into the soil quickly, with the second experiment pointing out that water soaks into grass during a normal summer at a slower rate.

In the final experiment, the water is placed on what appears to be dry grass and does not appear to move, highlighting the potential for flash flooding if heavy rains follow a heat wave.

Dr Thompson told the PA news agency: ‘Britain is desperate for rain to break this drought.

“But we have to be careful what we wish for.

“Experience around the world has shown what can happen when heavy rains follow a very dry and hot period that has hardened the ground.

If you pray for rain, you should pray for two days of drizzle, terrible as that sounds.

Rob Thompson, University of Reading

“The water cannot infiltrate easily, most of it flows directly to the surface, which can quickly turn into flash floods.

“If you pray for rain, you should pray for two days of drizzle, as dreadful as that may sound.”

The Met Office retweeted the post and added: ‘Dry ground takes longer to absorb water after a #heat wave than if it were a normal summer. This experiment shows how heavy rains after a long period of extreme heat can lead to flooding.

Temperatures have continued to soar across the UK and drought is expected to be declared in parts of England.

The National Drought Group – made up of government and agency officials, water companies and other groups such as the National Farmers Union – is due to meet on Friday to discuss the prolonged dry weather.

Drought is expected to be declared in the worst affected parts of England in the south and east, following the driest July on record for some areas and the driest first half since 1976.


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