Why is heavy rain so dangerous after a heatwave? This clever video illustrates the reason

The UK is expected to experience heavy rain and floods over the next few days

(Image credit: RUBEN BONILLA GONZALO / Getty)

Most of us are happy to see the back of the heatwave in the UK, with rain expected in the next couple of days, but some experts are worried that we'll have flash floods - due to how dry the ground is.

However, if you're a little confused about how this could happen, a very clever video, which a university professor posted on Twitter, shows exactly why dry ground in a heatwave can be dangerous when rain follows straight after.

The video perfectly illustrates how water, or rain, soaks into the ground on wet grass, during a normal summer, then during a heatwave.

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Whether you have found it too hot to work during the heatwave or you're wondering if you can burn more calories in the heat, most of us are looking forward to some cooler weather in the UK, as temperatures soared up to 36 °C (96.8 °F) last week.

However, weather experts issued an amber warning on Monday for thunderstorms, meaning flooding and travel disruption are likely for the southwest of England. 

Most of us would assume that, after a heatwave, the ground needs some rain, but the professor from Reading University has illustrated how the ground changes after a heatwave.

Posting the viral video, which has already had nearly 45,000 likes and 19,000 retweets on Twitter, it shows how water soaks into three different types of ground - on wet grass, soil during a mild summer and after a heatwave or drought.

The video, by Dr Rob Thompson, shows three glasses of water, with the same amount of water in, all turned over on the three different grounds. The water soaks up the quickest on the wet grass, while the second one, which is how the soil and grass would look in a normal summer, follows, soaking up the water three times slower than on the wet grass.

However, by the end of the video, the water on the parched ground is only a quarter soaked in, with most of it remaining in the glass - showing just how slowly rain soaks into the ground after a drought, and how floods can occur. 

The video was accompanied by an explanation, which said, "In this experiment Dr Rob Thompson of @UniRdg_Met shows just how long it takes water to soak into parched ground, illustrating why heavy rainfall after a #drought can be dangerous and might lead to flashfloods."

Sarah Finley

Sarah is a freelance journalist - writing about the royals and celebrities for Woman & Home, fitness and beauty for the Evening Standard and how the world of work has changed due to the pandemic for the BBC. 


She also covers a variety of other subjects and loves interviewing leaders and innovators in the beauty, travel and wellness worlds for numerous UK and overseas publications. 


As a journalist, she has written thousands of profile pieces - interviewing CEOs, real-life case studies and celebrities - interviewing everyone from Emma Bunton to the founder of Headspace.