London's defences against climate change to tackle heat and rain

The mayor of London has outlined his strategy to protect the city from the effects of global warming, including turning the rooftops of the city into gardens to soak up downpours
David Adam
guardian.co.uk,
Friday August 29 2008 17:06 BST

To some they are a rural escape in the centre of the city, to others they are a chance to test their green fingers and design skills. Now London mayor Boris Johnson has found a new use for urban roof gardens – as a key weapon on the frontline against global warming.
An increase in the number of rooftop gardens to soak up rainwater across the capital is among a series of measures suggested by Johnson today, as part of efforts to prepare London for the effects of climate change.
The mayor's adaptation strategy, billed as a world-first, aims to address the challenges of flooding, extreme temperatures and drought. It calls for compulsory water metering, greater awareness of flood risks, and more tree planting, alongside stronger efforts to resist attempts by local authorities and insurance companies to fell existing urban trees.
The mayor's team said they were also looking to copy a heatwave emergency plan used in US cities including Philadelphia, where old and vulnerable people are collected in air-conditioned buses and taken to cool public buildings. They said libraries, shopping centres, churches and offices across the city could be used.
Johnson, who has previously dismissed the Kyoto Protocol, which regulates international carbon emissions, as "pointless" and said anxiety over climate change was "partly a religious phenomenon" said the 2006 Stern Review which investigated the issue had convinced him of the need to act. "When the facts change, you change your mind," he said.
Launching the strategy at the Thames barrier, he said: "We need to concentrate efforts to slash carbon emissions and become more energy efficient in order to prevent dangerous climate change. But we also need to prepare for how our climate is expected to change in the future. The strategy outlines in detail the range of weather conditions facing London, which could both seriously threaten our quality of life, particularly that of the most vulnerable people, and endanger our pre-eminence as one of the world's leading cities."
He said all major cities were at risk from climate change, and that the strategy, which is a legal requirement under the Greater London Authority Act, put London in a strong position. "London is not unique. All major cities such as New York and Tokyo are at risk from climate change."
The strategy does not address so-called mitigation of climate change, measures to reduce emissions, but Johnson said he supported a target set by previous mayor Ken Livingstone to slash carbon pollution 60% by 2025. He said measures to meet the target would include incentives for Londoners to better insulate their homes and switch to more efficient condensing boilers. His team is assessing whether households could be given council tax rebates for adopting such energy-saving measures.
Global warming is expected to give London and its surrounding area longer, hotter summers as well as warmer, wetter winters with the added problems of more frequent heat waves, droughts and flash floods from rising sea levels and downpours. Some 600 Londoners died as a result of the 2003 heat wave that killed about 15,000 in France, while low rainfall during 2004 and 2005 led to water shortages in the capital.
Some 15% of London is deemed at high risk from flooding due to global warming – an area including 1.25 million people, almost half a million properties, more than 400 schools, 75 underground and railway stations, 10 hospitals and London City airport. At stake is an estimated £160bn worth of assets, not just in London, but along the banks of the Thames estuary, where large housing developments are planned.
Johnson said work was under way to address stifling summertime temperatures on the underground network, with air cooling on sub-surface tube lines to begin in 2010. By 2015, he said all trains on subsurface lines, around 35-40% of the network, will be air cooled.
The draft adaptation strategy, which will be finalised next year, calls for a citywide 'urban greening' programme, using green spaces and trees to absorb and retain rainwater, and pledges to map London's drainage network to reduce surface water flood risk. It also recommends greater use of rainwater harvesting and "grey water" recycling in new buildings, as well as London-specific guidance for designers and architects to reduce the risk of buildings overheating in summer.
Jenny Bates of Friends of the Earth said: "It is essential that the capital prepares for the impacts of climate change, which is already affecting Londoners through increased flood risk, heavier and more frequent downpours and extreme heat.
"But Boris Johnson is also committed to cutting London's carbon dioxide emissions by 60% by 2025 in order to prevent dangerous climate change, and has so far failed to explain how he will achieve this. The mayor must provide a comprehensive action plan for reducing London's emissions that includes ways to make it cheaper and easier for Londoners to go green."