Risk of flash flooding during the heat wave illustrated in a simple video experiment


With nothing more than three cups of the watera British scientist clearly illustrated how Drought conditions may increase the risk of flash flood as soon as the rain starts to fall.

In the experiment, Dr. Robert Thompson of the Reading University‘s Meteorology Department, filmed himself at different times of the year flipping a clear plastic cup filled with water on the same piece of ground.

The images clearly reveal how Weather report conditions affect the rate of water absorption.

In wet but not waterlogged conditions, the water in the upturned clear plastic cup immediately sinks into the wet ground.

In the dry conditions of a ‘normal’ UK summer, in which some rainfall means the ground has been watered recently, the cup of water takes longer to soak into the ground.

And in the final video – filmed during the current heatwave and near-drought conditions the UK is experiencing – the water remains in the overturned cup, unable to make its way through the hard, dry ground.

Talk to The IndependentDr Thompson said: “Dry, parched soil does not allow water to enter as effectively as soil that is already moist. There are a number of reasons that occur, but [among the most important are] that the soil is compacted because the moisture has been removed by evaporation and cooking.”

Additionally, he said, “Soil particles become more ‘hydrophobic’, repelling water, and surface tension then helps to keep water from falling through microscopic cracks in the soil. Because soil resists entering the water, the water remains on the surface. , to slide down the slopes or simply to sit in a swimming pool.”

He said he was “surprised by the magnitude of the effect”.

“I think part of the beauty of the experience is that it’s easy for anyone to repeat, you just need a glass and some water.”

But it also highlights the huge risk of flash flooding after dry weather – something seen in recent days in the famously hot, dry region of California. death valleywhere a “one in a thousand year” deluge washed away roads, damaged infrastructure, swept away cars and left hundreds of people behind.

It all happened with just an inch and a half of rain in a single day – which officials said was close to the region’s single-day rainfall record.

Dr Thompson said: “Once you look at larger areas and add the water as heavy rainfall, you have the effect [seen in the experiment] takes place over a large area, and the trickling water, unable to penetrate the ground, becomes a problem as it can cause flash floods.

“It will also remain on the surface where it evaporates more quickly, and heavy showers will often be followed by sunny spells to encourage this, so it will not help current water shortages as effectively as it will. could.”

He added: “However, heat waves usually end in heavy showers and thunderstorms, rather than a day of drizzle which would really benefit the current situation. As 1976 often returns, when the drought broke, the rain has caused flooding in parts of the country.”


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