As the UK moves from a record-hot May into an unseasonably wet June, the risk of flooding is being exacerbated by a proliferation of paved gardens, according to the country’s flood insurer of last resort.
The trend — often a quick fix to create space to park cars or to make garden maintenance easier — is emerging as a major factor in predicting how badly flo
ods will affect homes. The more asphalt and the less spongy vegetation and natural ground, the bigger the risk.
The conventional wisdom is that “lower maintenance is better,” says Kelly Ostler-Coyle, director of corporate affairs at Flood Re, which has served as a backstop for Britain’s commercial insurers since 2016.
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But with Britons increasingly paving their outdoor spaces, “you’re finding that places that have never flooded before are now experiencing low level surface water flooding,” she said.
To drive home its point, Flood Re last month sponsored a garden at the Chelsea Flower Show, which is the absolute high-point of Britain’s horticultural calendar and regularly attended by Britain’s royals.
As a model for the ideal UK garden in a small space, Flood Re displayed a Mediterranean-style courtyard planted with wood ferns well-suited to moist, shady spots. It also included tree species such as the Persian ironwood and th
e yew, as part of a theme focused on planting for a hotter climate with more turbulent weather patterns.
Gardens make up almost 5% of Britain’s total land area, rising to 41% of land in London, according to the Royal Horticultural Society, a charity. But instead of teeming with vegetation, a growing number are full of concrete and paving slabs.
In England, the Climate Change Committee estimates that the total area defined as permeable enough to absorb rain fell by about 173,000 acres between 200
1 and 2022; that’s roughly equivalent to the size of Singapore. In cities across the UK, permeable land fell from 63% to 54% over the two decades through 2022.
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As Britain loses much of its natural sponginess, climate change has made sudden downpours both more frequent and more intense. Every extra 1C (1.8F) of heat
adds an estimated 7% of additional moisture to the atmosphere, which scientists say is contributing to heavier summer downpours.
Meanwhile, Britain is warming faster than the global average. And “surface-water flooding is the fastest-growing climate risk at the moment,” says Ostler-Coyle.
With more homes in danger of flooding, insurers are increasingly passing the risk on to Flood Re, which warns that the vulnerability of homes will increase with clima
te change. That, in turn, will raise the burden on the wider public, whose insurance premiums fund Flood Re.
“Increased paving over green spaces is intensifying the risk of surface water flooding,” said Laura
Hughes, head of general insurance policy at the Association of British Insurers. “To tackle this, prevention
must come first. Permeable paving and green spaces can soak up surface water, easing the strain on drains and reducing the likelihood of flooding.”
For a template of what might lie ahead, insurers look back to July 2021, when surface-water fl
ooding devastated England’s east and south east, including the capital. Some of London’s wealthiest areas were among the hardest hit, resulting in a spike in insurance costs and in more high-end properties being excluded fro
m commercial insurers’ books and handed over to Flood Re.
All that paving has a “cumulative effect” and drives up property risk for homes across the country, says Hannah Davidson, an underwriter at the insurer Aviva. “It’s
that sudden downpour leading to a massive accumulation of water, where the drains just can’t cope, that’s causing that surface water risk.”
Surface-water flooding can lead to “the drains backing up, coming through doorways, coming up through the floor, through the air vents,” she said. If a homeowner chooses to create “a huge area of impermeable surface, that water has only a few places to go, and it’s either into the street or potentially into your property.”
