Londoners have been told to brace for significant flash flooding if downpours hit the capital.
Dry soil doesn’t absorb water as quickly, which means that when it rains, the city is much more likely to face problems like last summer.
Experts warned urban drainage systems may not be able to handle a sudden heavy shower as water would likely run off land that has dried up over weeks of little rain and hot weather.
There is currently one Yellow warning from the Met Office for thunderstorms across most of the country.
The organization’s weather forecaster Dan Stroud explained: “(The storms) will help (the drought) a little bit, but to be honest it’s almost the wrong kind of rain.
“What we are likely to see are heavy, intense downpours.
“When the soil is baked that dry, it’s very difficult for the soil to really absorb the water very quickly… In those circumstances, the water runs off and we can potentially have runoff issues, so some flash flooding.”
As the climate changes, the UK is likely to experience increasing cycles of hot weather, drought and flooding.
The Met Office issued a yellow thunderstorm warning for most of the UK on Monday and Tuesday and southern parts on Wednesday, adding it could cause flash flooding, traffic disruptions and power outages.
Adding to the warnings today, Mayor of London Sadiq Khan said: “We learned a lot from July last year when flash floods hit in just a few hours, caused by a huge torrent of rain – two months’ worth of rain – were caused and people’s houses, shops and public transport were flooded.’
“Speaking to the Met Office, the Environment Agency and many others, we are concerned that we could see a large amount of rain in a short period of time over the next few days, which could lead to flash flooding,” the mayor continued.
“I have written to tens of thousands of Londoners who live in homes at risk of flash flooding.”
He added: “My message to Londoners is please contact Floodline, visit your local authority website to see what you can do to reduce the chance of flooding but also the consequences for you to minimize.”
Mr Khan also recommended people to check they have insurance and prepare a grab bag if they have to go.
“The bad news is that if it rains heavily in a short period of time, flash floods could well occur,” he warned, urging the government to do more to combat climate change.
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“I’m really concerned about the ability not only of the fire service but also of our city to deal with heatwaves, droughts and flash floods which are now becoming a regular occurrence,” Mr Khan said.
He also stated he was “really concerned for all life forms in London” as temperatures hit 35-40°C, as it called for adjustments in workplaces and homes, and measures to combat fires.
The National Drought Group placed parts of south-west, south, central and east England on official drought status last week, while six water companies have imposed or announced plans to introduce hose line restrictions.
But Professor Hannah Cloke, a hydrology expert at the University of Reading, explained why the rain wouldn’t be a significant help – and instead could lead to dangerous flooding in cities.
“If it’s raining heavily in a city, the drainage system can handle it to a point, but if it’s raining really hard it can overwhelm the system — the rain can’t drain fast enough,” she said.
Professor Cloke also pointed out that “really very dry” parks mean there is nowhere for the water to drain.
“Water usually seeks the deepest path – that’s why it’s so dangerous for cities with such extensive flooding. That’s why it’s about the subway and underground car parks and the like.’
On why heavy rain wouldn’t alleviate drought areas, she added: “It’s really a drop in the ocean. It doesn’t penetrate the soil like we really need it to. We need it back in the system where it can be stored.
“We really need a long rainy winter to replenish that.”
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https://metro.co.uk/2022/08/15/london-faces-flooding-when-storms-arrive-after-warning-of-wrong-kind-of-rain-17187362/ London faces flooding as storms hit after warning of 'wrong type of rain'