Downpour in November last year saw 316.4mm of rain fall – a once in 1,800 years event, scientists have said

This article is more than 9 years old

This article is more than 9 years old

The 316.4mm (12.45in) of rain that fell at Seathwaite Farm in Borrowdale, Cumbria, on 19 November last year was by some way Britain's heaviest recorded rainfall over 24 hours and statistically a once in 1,800 years downpour, government scientists said today.

"It was very rare indeed – an extreme event of international significance," said Jamie Hannaford, a scientist at the Centre for Ecology and Hydrology.

"What fell in 24 hours in the Lake District then was about half what you get in a whole year at somewhere like Gatwick, near London".

New research into the frequency of such storms shows that the prolonged rain over north-west England and southern Scotland that week led to many rivers doubling their previous highest-ever peak flows. Records were set at 17 river monitoring stations.

The rain in Cumbria also proved too much for the lakes to cope with. Normally, Hannaford said, they act as storage tanks, filling up when it rains and then releasing water gradually downstream.

But in this case they filled to capacity and then added to the problem by releasing vast amounts of water downstream. Ullswater was one metre higher than its previous highest recorded level.

"At such high levels, the lakes were less able to store the vast volume of incoming runoff, and instead water was rapidly transmitted into the rivers downstream, causing a much more rapid flood response", Hannaford said.

The previous heaviest rainfall in Britain was at Martinstown, in Dorset, when 279.4mm fell in 24 hours in 1955.

But this was nothing to the 1,825mm of rain that tropical cyclone Denise dropped on Reunion Island in the Indian ocean in 24 hours in 1966.