What happens when it rains after a drought? Reading Uni experiment raises fears of flash flooding

  • Watch University of Reading meteorologist Dr Rob Thompson's experiment

A University of Reading expert is warning the UK could be at risk of flash flooding, as he revealed in an experiment exactly what happens when it rains after a drought.

Posting a video of the experiment on Twitter, Dr Rob Thompson from the university's Meteorology Department used three glasses of water on different conditions to demonstrate how long it takes water to soak into the ground.

In the first experiment the water is placed onto wet grass and can be seen rapidly soaking into the ground.

The second example shows grass during a normal summer, and the water soaks in, though not as quickly.

But in the third experiment, the water is placed onto extremely dry ground, following a heatwave and struggles to absorb.

Dr Thompson said it illustrates why heavy rainfall after a drought can be dangerous and might lead to flashfloods.

  • Dr Rob Thompson

"A lot of us recognise that dry ground is harder to get watered, Dr Thompson said.

"So I knew it was going to be a problem, but I was surprised at just how big the difference was.

"The wettest grass took just nine seconds to empty the glass, 52 seconds for the second one. But I gave up with the driest one after four and a half minutes as you could see the water just wasn't able to go anywhere.

"Imagine if we get heavy rain - it's going to land on top of the hard soil. It might evaporate if it becomes hot and sunny again, or it could run down and cause flash flooding, so a real danger.

"What we need is hours of light rain that will slowly soak in."

Much of the UK's grasslands has been left parched following the hot dry conditions.

Parts of the South West, parts of southern and central England, and the East of England have moved into drought status, the Department for Environment, Food and Rural Affairs said on Friday. (12 August)

The majority of the country remains in ‘Prolonged Dry Weather’ status.

It means the Environment Agency is taking precautionary actions, and is enhancing its monitoring and protection of water resources, along with the water companies.

The Government says most water companies are maintaining good reservoir storage for summer demand.

However a number of water companies have already introduced hosepipe bans.

Southern Water customers in Hampshire and the Isle of Wight are already under what's known as a Temporary Use Ban (TUB).

South East Water is introducing the same restrictions from Friday 12 August.

And Thames Water which provides water to people living in the Thames Valley and parts of London, has confirmed it will announce a hosepipe ban in the coming weeks.