Climate change could more than double flash-flood risk in London

Danger that extreme rainfall of 30mm an hour, in worst-case scenario could increase 2.5 times by 2070

Extreme rainfall linked to global warming could trigger more flash flooding in the UK. Getty

Flash flooding in London could become 150 per cent more likely in the next 50 years because of climate change, Britain’s top weather forecasters said.

The warning from the Met Office echoes findings by the world’s top climate scientists that a hotter planet will be more prone to natural disasters.

It said in the worst-case scenario – if insufficient action is taken to tackle climate change – the danger of extreme rainfall will more than double by the 2070s when compared with risk levels in the 1990s.

This would involve 30 millimetres of rain falling in the space of an hour on an area as small as a neighbourhood of London.

A reading of 4mm per hour or more is considered heavy rain by the Met Office, while a threshold of 30mm will trigger flash-flood warnings.

“These results suggest a big increase in the frequency of flash-flood-producing rainfall events,” the UK forecasters said.

Parts of London recorded up to a month’s rainfall in an hour in July last year, in a glancing effect from a weather event that went on to cause devastating floods in Western Europe.

Although attributing specific events to climate change is difficult, those floods led to widespread calls for tougher action on global warming.

The worst-case forecast is based on a scenario called RCP8.5, which assumes that the Paris Agreement goals of limiting global warming to 1.5°C or 2°C above pre-industrial levels are not met.

Alok Sharma, who presided over the Cop26 summit last November, said this week that the summit had kept the 1.5°C target alive but that it would “slip from our grasp” if the promises made in Glasgow are not met.

Met Office scientists called for more research into dangers known as high-impact, low-likelihood (Hill) events that could go beyond one-off weather disasters.

These could include a change to the North Atlantic jet stream that warms the UKs climate. Parts of the English coastline are already disappearing because of rising sea levels and other seaside towns are under threat.

“Both the climate science and policy communities would benefit from devoting more attention to Hill events,” said Dr Richard Wood, a Met Office climate expert.

“We can be sure that higher levels of global warming will make them more likely.”