Two-fifths of London firms at risk of climate-fuelled flash floods

Flash floods fuelled by the climate crisis threaten more than two-fifths of businesses in London, highlighting the scale of potential disruption the capital faces from increasingly extreme weather.

Of London’s 301,000 commercial buildings, 42% are at risk of being hit by surface water flooding, which caused chaos last summer when torrential downpours struck the city.

The analysis, by insurer Zurich UK, reveals the potential impact of climate-driven weather on London’s economy. It comes after Zurich’s data scientists pinpointed every commercial or mixed-use property in the city and mapped them against areas at risk of flooding from heavy rain.

The borough of Kensington and Chelsea was found to have the highest percentage of buildings at threat of flash flooding (63%), followed by Hammersmith and Fulham (56%), Merton (54%), Southwark (54%) and Wandsworth (53%).

Last July, London homes and businesses were inundated when a month’s worth of rain fell in one day, with basements properties among the hardest hit.

Zurich’s analysis reveals nearly half (14,780) of London’s 33,205 basements properties in commercial use are exposed to surface water flooding. Of these, 5,692 face a “high” or “extreme” flood risk, with the greatest number of buildings in Westminster.

David Nichols, Zurich UK’s Chief Claims Officer, warned that failing to prepare for more regular bouts of heavy rain could have a knock-on impact on London’s economy which accounts for a quarter of the UK’s GDP. (1)

“Flash floods are one of the most serious climate threats facing the capital,” he said. “Even at current levels of global warming, we saw the chaos heavy rains caused last year. More frequent and severe rainstorms could be hugely disruptive for Londoners, businesses and the city’s economy. Extreme weather is the new normal, and businesses need to adapt. It’s crucial that firms urgently assess the flood risks they face and put in place plans to respond and recover.”

Claire Harding, Research Director for The Centre of London, said: “London faces increasing risks from heatwaves and flash flooding: and our aging infrastructure isn’t keeping up. The impacts will often be worse for Londoners living in inner city areas with high population density and little green space. As well as making fast and steep cuts to our carbon emissions, government at all levels must invest in changes which make our city more resilient: improved drainage systems, green spaces that can act as giant sponges, and trees for shade and soil stability.”

Hugh Ellis, Director of Policy, Town & Country Planning Association, said: “It’s vital Government take stronger action to face the climate crisis by putting flood risk at the heart of the planning reform agenda. A failure to act now puts people at risk and creates long term costs to our economy.”

According to the Met Office, extreme rainfall in the UK could become more frequent and severe than previously thought. New calculations suggest that 30mm of rain per hour – the threshold for flash flooding – could be two-and-a-half times more likely in London by the 2070s, compared with the 1990s (2).

Paving over of the capital, a lack of green spaces and increased use of basements, is piling pressure on London’s antiquated sewage system, contributing to the rise in surface water flooding. 

One solution is the roll out of so-called Sustainable Drainage Systems (SuDS). These are greener alternatives to traditional drainage solutions and include features such as porous pavements and road surfaces, below ground storage areas and changes to landscaping in parks and green roofs on buildings. SuDS help to retain or delay rainfall running from roofs or land from entering the sewers. However, there are currently no binding requirements or obvious sources of funding for Councils to include SuDS in public spaces.

Nichols added: “It’s not too late to prepare our towns and cities for more surface water flooding, but the current the pace of change is too slow. The government needs to accelerate the retrofitting of sustainable drainage in public spaces, or rainfall will increasingly overwhelm city sewers.”

Zurich has recently launched a build back better scheme to help flood-hit home and business owners improve their property resilience to future flooding. It also offers a free counselling service for customers impacted by flooding.

Four ways to protect your business from flooding

• Check your flood risk – whether you’ve operated from the same location for years, or recently moved in, assess the long-term flood risk in your area and sign up for flood warnings. Zurich produces guidance on how to assess your flood risk.
• Protect your property – take action to make your business more resilient to flooding. This can reduce the impact of floodwaters and help you return to business sooner. Actions range from cost-free measures such as shifting expensive equipment to higher floors and regularly backing up data to moving plug sockets higher up and investing in non-return valves, to stop sewers backing up.
• Prepare a flood plan – if your business is in a flood prone area, do what you can to prepare for a flood now. This can include drafting a flood plan, so you have crucial information to hand, such as key locations for electricity cut off, and a list of actions if a flood is imminent, such as moving stock or computer servers. Zurich has created a free Flood Emergency Response Plan.
• Write a business continuity plan – make sure you factor in climate shocks such as floods into your business continuity plan. Having a plan in place can help you prepare for the unexpected and keep your business running if disaster strikes.
• Carry out a climate risk assessment – work with experts to identify how current and future climate change could impact the operations of your business. The more you know about the risk, the better you can prepare. Zurich, for example, offers Climate Change Resilience Services to help customers assess and mitigate their climate risks.

Top 10 Greater London boroughs by total percentage of commercial and mixed-use buildings at pluvial flood risk

(1) ONS data shows London accounted for 22.7% of total UK GDP in 2019 https://www.cityam.com/london-and-south-east-now-accounts-for-4-in-10-of-total-uk-economy/
(2) Met Office : Future extreme rainfall more extreme than first thought https://www.metoffice.gov.uk/about-us/press-office/news/weather-and-climate/2021/future-extreme-rainfall-more-extreme-than-first-thought

Methodology

Each commercial unit in London was identified by its Unique Property Reference Number.

For each unit, the presence of a basement was found by using inspection data from the Valuation Office Agency.

This unit information was then aggregated to a building level using the Parent Unique Property Reference Number. This gave the number of buildings in London which are used (either partly or totally) for commercial use and whether these buildings had a basement.

The flood scores (as provided by Ambiental) were appended to the building. The resulting data was then aggregated to give summaries by London Borough.