Flash flooding: Droughts Need Water, Just Not so Fast

After weeks of scorching heat and dry conditions in the majority of the UK, with drought announced in parts of England, it seems that a big downpour is what we need.

However, the heavy rainfall and thunderstorms predicted by the Met Office this week might be a threat.

Researchers are warning that the storms can cause flash flooding and are possibly not going to replenish dry soils.

Here is why torrential rain might not be what dry land needs at the moment.

Flash flooding

In addition to two heatwaves and record-breaking heat levels this summer, lots of parts of the UK have seen far-below normal rainfall. As stated by the UK Center for Hydrology and Ecology, this has baked the soils, leaving them dry and hard with extremely reduced moisture levels.

The soil cannot absorb the water fast enough if rain falls in big quantities and at high speed, as in thunderstorms. Rather it accumulates on the surface. On steep surfaces, that water quickly runs, triggering flash flooding.

Dr. Rob Thompson, a meteorologist at the University of Reading, explains that the effect resembles pouring water at high speed on concrete.

Dr. Thompson says, “Grounds of our gardens, parks, and farmlands are now all potentially as dry as tarmac and concrete gets. Areas that aren’t tarmac will behave like tarmac when rain hits them”.

Prof John Quinton at the University of Lancaster explains that the primary impact droughts have on soil is known as hydrophobicity.

When water strikes a water-proof coat, it is pushed back, creating droplets on top and, at some droplets, running off. A comparable thing occurs when organic matter in the soil dries, creating a layer of product that stays out of water.

Prof Quinton states stated, “Rather than water relocating right into the dirt, it remains on the surface area rather”.

 Soil arrangement

It is also difficult not to notice how the drought decimated grasses and other flora, transforming parks and fields yellow. These typically develop a cover over the soil, guarding it against heavy rainfall.

Prof Quinton clarifies, “Vegetation breaks up big thunderstorm raindrops into smaller drops. Without that protection, the big drops damage the soil structure, meaning even less water can infiltrate”.

Dr. Thompson explains that while the UK has great deals of different soils, the entire nation is prone to flash flooding if the rain hits hard enough.

Anywhere with steep-sided, uneven terrain, where water can move considerably rapidly, is at high risk.

While it is not likely to be as damaging as the devastating flooding in Germany and Belgium last summer, suggests Dr. Thompson, the possibility is always there.

Thunderstorms can produce massive quantities of rainfall, however, typically in a small area and a brief spell. That does not provide the soil with adequate time to recover.

Researchers state that light rain over several hours and days will bring soils back to a normal level.

However, weeks of above-average rain are possibly required to bring an end to the drought.

Researchers have stated that the record-breaking temperatures registered in July would have been “virtually impossible” without human-caused climate change and that heatwaves and droughts are probably to end up being more severe and frequent.

Originally published by: BBC