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The Urban Umbrella: Street Trees Stem Flash-flooding
Localised urban flooding could be alleviated by cost-effective urban tree programmes, research compiled by the charity Trees for Cities suggests.
The urban umbrella
City trees work in two ways: intercepting water at the canopy, and absorbing surface water through their roots. Rainwater is drawn up through the tree in the process of transpiration and it is eventually lost to the atmosphere through stomata on the underside of the leaves.
By removing rainwater from the local environment, they slow the rate of sudden, heavy rainfall. This reduces the peak volume of water needing to be displaced during the storm, and so avoid the need for expensive man-made floodwater containment systems, and the risk of sudden, devastating flooding.
The average cost when a UK home is flooded is between £20,000 and £30,000.
London’s tree canopy cover should increase from 20 to 25% by 2025 under the Mayor's tree programmes, to make a quarter of the city green from above.
In England, a study in Northumberland calculated the value of woodland areas around a river, in terms of the offset engineering costs of flood control, at £1,200 per hectare. In our changing climate, woods around urban areas and the trees within them are in especial need of protection for them to carry on providing these benefits .
In the city of Atlanta, USA the American Forests organisation calculated that if trees were removed, the cost of building containment facilities for the floodwater runoff would be $2 billion.
This means that for every $1 spent on trees, $5 can be recouped in money saved.
Trees for Cities
Sharon Johnson, Chief Executive of Trees for Cities said: “Over recent years we have seen a real difference in the attitude taken to trees in UK cities. They’re becoming much more valued as an asset to the community, providing a wealth of cultural and financial benefits.
“As a charity, we’re committed to increasing awareness of these benefits: our streets are community spaces, and so many are an untapped resource for the people who live on them. We’ve been proud to be planting trees across the country, through individual donations and tree planting schemes, so that residents can enjoy their benefits for hundreds of years to come.”
For further information, contact Stephen Gray, stephen.gray@
Notes to Editors
Trees for Cities is an independent charity which plants trees and landscapes public spaces in urban areas. The charity’s vision is to stimulate a green renaissance in cities around the world that will beautify the urban landscape, and encourage greater social cohesion through the active participation of local people. A special effort is made to involve children and young people in all of the projects. The public can get involved by sponsoring trees, registering as a volunteer, enrolling in training programmes, taking part in the annual Tree-Athlon and going to fundraising parties – see www.treesforcities.org for more information.
‘Trees Matter!’, National Urban Forestry Unit, 2005
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An independent charity which plants trees and landscapes public spaces in urban areas in order to beautify and protect the urban landscape, encouraging greater social cohesion through the active participation of local people.
Page Updated Last on: Mar 09, 2010