The amount is almost the same as 10 times the water held in the London Serpentine lake in Hyde Park.
The news comes as the forestry industry launches a petition calling on the Government for more tree planting to prevent flooding.
Last week the Environment Agency announced that planting trees around rivers could reduce the height of flooding in towns by up to 20 per cent.
The research (link below) which was carried out by Treeconomics and Forest Research, was commissioned by the Mayor of London’s office and the Forestry Commission.
It was endorsed by national bodies including Natural England, the Tree Council and the London Tree Officers Association.
The avoided water run-off is calculated as saving the London taxpayer £1.5m every year.
Kenton Rogers, tree expert and environmental scientist with Treeconomics said: “Trees are the most simple and cost effective solution imaginable to combat the threat of climate change and changing weather patterns.
“This report proves beyond doubt that trees, particularly deciduous mature trees, have a central part to play in flood prevention. This research (and other similar work we have done) can be used as a benchmark for flood prevention in this country.
“We should really be looking to invest in far more tree planting in the years to come and maintain and enhance the existing tree cover.”
As well as flood prevention the research also found huge benefits for pollution absorption, carbon capture and storage, as well as city cooling in the summer months.
The project was aided by the work of over 300 volunteers, who surveyed and mapped the trees. The cost-benefit calculations were then carried out by computer modelling, on a system known as i-Tree Eco.
The community involvement in measuring and appreciating the benefits of the urban forest was an important aspect of the overall programme.
Key findings from the Greater London project
• Greater London has a total tree population of approximately 8.5m (a tree for every Londoner)
• Inner London has a total tree population of approximately 1.6m
• Trees across greater London capture and store 77200 tonnes of carbon every year, to the value of £4.63m
• Pollution absorption is calculated at 2241 tonnes every year across greater London, valued at a cost of over £100m per annum
The link to the report is here – http://www.treeconomics.co.uk/projects/londoni-tree