Monday, December 05, 2022

Why can rain be so dangerous after a drought?

After weeks of scorching heat and days without a drop of rain – and parts of England officially declared dry, the UK is ready for heavy rain to come.

But although it may seem like a relief at first glance, the torrential downpour (predicted by the National Meteorological Office, the Met Office), actually represents a danger.

Scientists warn that this condition can cause Flooding And they are unlikely to allow dry soil to be replenished.

These results concern not only the United Kingdom, but also other countries europa in the grip of drought.

Why can rain cause floods?

As well as two heatwaves and record temperatures this summer, many parts of the UK have received much less rain than normal.

The UK Center for Hydrology and Ecology notes that this has left soil dry and hard with very low moisture levels.

If rain falls in large quantities and at high speed, as in thunderstorms, the ground can’t absorb damp.

Instead, it accumulates on the surface. On sloping surfaces, water flows rapidly, causing flash floods.


The effect is like pouring water on cement at high speed, University of Reading meteorologist Rob Thompson tells the BBC.

“The grounds of our gardens, parks and farms are now potentially as dry as asphalt and concrete. When it rains the non-asphalt areas will behave like asphalt,” he says.

This video, recorded by Thompson, clearly shows how Earth reacts on contact with water.

The main effect that drought has on the soil is called your hydrophobicitySoil scientist John Quinton of Lancaster University explains.

When water hits the waterproof jacket, the jacket material repels it, causing beads to build up and eventually run off.

Something similar happens when the organic matter in the soil dries out, forming a layer of material Prevents water penetration.

“The water stays on the surface instead of going down to the ground,” Quinton says.

soil structure

Drought has burned grass and other plants, turning parks and fields yellow.

This vegetation usually covers the ground and protects it from heavy rains.

“botanical” break the drops Of rain in small drops from a big storm. Without that protection, larger droplets damage soil structure, meaning even less water can infiltrate,” explains Quinton.

Thompson says, while the UK has many different soil types, if there is enough rain, the entire country is prone to flooding.

Getty Images

any place with steep land And hills, where water can move very fast, are at particularly high risk.

Thompson says the floods are unlikely to be as devastating as last summer’s floods in Germany and Belgium, but the possibility is always there.

Thunderstorms can cause large amounts of rain, but usually over a small area and over a short period of time. This does not give the ground enough time to recover.

Scientists show that the norm after a drought is a Light rain for several hours and days so that the soil can regain its normal moisture level.

But ending the drought will probably require weeks of average rainfall.

Record temperatures observed in July would have been “nearly impossible”, according to researchers Climate change Humans are caused, and heat waves and droughts are likely to be more extreme and common.

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