Viral Video Experiment Shows Why Flash Floods Follow Heatwaves

Droughts and flooding are two sides of the same coin.


Tom Hale

Senior Journalist

clockAug 16 2022, 09:23 UTC
A silhouette of a old man and his bicycle getting caught in a flash flood following ran.
One part of Death Valley National Park recently experienced flashing flood after 75 percent of its yearly rainfall fell in 3 hours following a hot summer. Image credit: Mathee Suwannarak/

Huge parts of Europe and the US have been grappling with record-breaking heatwaves this summer. However, as the heat starts to loosen its grasp, many areas could soon be faced with another weather woe: flash flooding. 

Floods and droughts are two sides of the same coin. In drought-prone areas, it’s often not unusual to also see flooding at different points of the year. This is because dry and baking hot weather can cause soil to harden, making it tougher for water to drain through. This makes the dry land prone to flash flooding if it does receive a sudden downpour of rain. 


This point was beautifully illustrated by a recent video on Twitter that went viral last week (below). Dr Rob Thompson, a meteorologist from the University of Reading in the UK, carried out a fun experiment using three upside glasses of water on different grass surfaces – wet grass, normal summer, and after a heat wave – and observed how quickly each drained.

The glass on the wet grass quickly glugged down, while the grass you’d typically see during a “normal” summer slowly but surely drained. However, the baked grass after a heatwave barely let any water through at all.

If you want to see how this might appear in the real world, then look no further than Death Valley (video below), the record-holder for the highest air temperature ever recorded on the planet. Earlier this month, the Furnace Creek area of Death Valley National Park reported around 3.71 centimeters (1.46 inches) of rain in less than three hours – about 75 percent of what that region typically receives in an entire year.


The result was dramatic flooding, swamped roads, and widespread water damage.

"The heavy rain that caused the devastating flooding at Death Valley was an extremely rare, 1000-year event,” Daniel Berc, a meteorologist with the National Weather Service Las Vegas, said in a statement. “A 1000-year event doesn't mean it happens once per 1000 years, rather that there is a 0.1% chance of occurring in any given year." 

Death Valley is a place of extremes, so we shouldn’t expect all parched parts of the planet to see this scale of flash flooding. However, it’s clear that climate change is likely to make drought and flash flooding all the more likely and even more severe in years to come. 


“Human caused warming of climate is intensifying the global water cycle and disrupting weather patterns leading to more severe droughts but also more serious flooding events across the globe,” said Professor Richard Allan, a climate scientist at the University of Reading, commenting about the current drought in the UK. 

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