The history of severe rain fall events in the area
This event, though clearly severe, was not that exceptional for
the area and has occurred before in living memory, notably the Lynton -Lymouth disaster of 1952. There have
been a number of other
local severe summer flooding events near or on the north coast of the South West peninsula.
These have
included an event on August 6-7th 1770 when a great flood devastated Lynmouth (Devon); perhaps
a forerunner of the 1952 storms and floods, and it seems, anecdotally, that there may have been perhaps even heavier
rainfall.
In the more recent past, on the 28 June 1917 Bruton, Somerset, 242.8 mm
of rain fell in 24 hours although this wasn't a local event though as such. In Somerset the rain began late in the
afternoon of the 28th, peaked in the middle of the night and contined until midday on the 29th. About 215 mm fell at
Aisholt, in the Quantocks, 213mm at Timberscombe, Somerset and 150 mm at Street, near Glastonbury. Look at the day's
synoptic chart here
On the 16 August 1924 at Cannington, Somerset,
238.8 mm fell in 24 hours. This was clearly a more localised fall with 215mm falling in just
five hours. In fact this remains the record daily rainfall for August, anywhere in the UK. Look at the day's synoptic
chart here
On the 6th August 1930 at Cheddar, Somerset
thunderstorms ensured that 111mm was recorded at Cheddar, Somerset in a short period, and the famous caves
were flooded. Look at that days synoptics chart here.
A few years later on the 4th August 1938 at Abbey
Park, Torquay 162mm fell in a severe thunderstorm that hit East Devon just before dawn. However it was
not that local, as 50 mm of rain fell in 6 hours over a large area from Tintagel to Exmoor and 100 mm was reported in an area
lying from Paignton on the south coast of Devon, north to Two Bridges on Dartmoor. Hailstones as large as small
walnuts lying 10 cm deep with four hours of almost continuous lightning were reported and severe flash flooding
followed. The day's synoptic chart is here
The most infamous flooding event in the area in living memory was on the
15-16 August 1952 at Lynmouth, Devon, when 229.5 mm of rain fell in 24 hours. This was the result
of heavy rain on Exmoor on the 15-16th. 228.6 mm of rain fell in 22 hours at Longstone Barrow, draining into the West Lyn
river. 275 mm is estimated to have fallen over parts of Exmoor and up to 300 mm is actually claimed to have
fallen in a day at Simonsbath. Although the event was preceded by 21 hours of heavy rain starting around noon on
the 15th it also followed heavy rainfall over preceding two weeks that had allowed high river levels and very waterlogged
ground. A seven hour long intense downpour from an almost stationary 'supercell' occurred in the late afternoon. There
was a sudden surge of water here, as seems to have happened in the 2004 Boscastle event.
The reason for this, as may well be found to be the case at Boscastle, is that boulders
and trees had created a large temporary dam upstream that suddenly gave way, and around 200,000 tonnes of huge boulders moved
rapidly downstream in the floodwater. The death toll was 34, twenty-eight bridges were destroyed and 93 houses ruined
or damaged so badly that they had to be demolished later and 420 people were left homeless; 28 cars were wrecked and another
38 disappeared out to sea. This was clearly on a different scale to the Boscastle event. The article here has a good discussion of the event and the day's synoptic chart is here
A few years later on the 8 June 1957 Camelford, Cornwall, (very
close to Boscastle) recorded 203.2 mm in 24 hours. This was perhaps the most similar of those documented here to the
recent Boscastle event. A thunderstorm led to 203 mm of rain falling, with 140 mm of it in two and a half
hours and about 70mm (nearly 3 inches) in one hour. Evidently there were hail drifts reported of up to 2 feet deep
and although some bridges were destroyed there was no loss of life. A synoptic chart for the day is here
Again quite locally, on the 14 June 1965 at Wadebridge,
Cornwall 140mm of rain fell in 220 minutes, in another similar event to Boscastle, which is very close. The
synoptic set up chart doesn't look all that concerning at first glance just here though, it must be said.
A few years later still, on the 10 July 1968 at Chew
Stoke, Mendips, Somerset 175 mm was recorded. This was not too localised however with 125 mm also
reported in 17 hours at Bristol,leading to flooding and damage. Many bridges were swept away though in the Somerset area.
Incredibly up to 125mm (5 inches) of rain fell on other parts of Somerset and Devon in just 90 minutes and several people
in Sidmouth, Devon drowned. The days synoptic chart is here
More recently on the 11-12th July 1982 Bruton, Somerset (nb see
June 1917) recorded 113 mm of rain in 16 hours; the River Brue burst its banks, leading to flooding and lightning strikes
led to power losses. The daily synoptic chart is here
In the far SW on the 22nd July 1983 Penzance, Cornwall flooded as
an area of low pressure brought thundery rain as it moved N from Biscay into very warm air over the UK. The synoptic
chart is here
In the last decade on the 9th June 1993 Culdrose,
Cornwall recorded 125mm of rain in the 9 hours to 09Z as a thundery low moved north from Biscay, 92mm of this
in the 2 hours to 08Z. The synoptic chart is here
It's also worth giving a mention, in closing, to the infamous 18 July
1955 Martinstown, Dorset event, 279.4 mm in 15 hours - though this was not related to an event near the
north coast. This is the British record for daily rainfall, 190mm- or nearly 7 1/2inches -fell in 4.5 hours.
The rain came with thunderstorms in two waves, the first starting at 2.30 pm and the second at 9 pm but the heavy rain
fell over a large area of Dorset eg Upwey, Dorset, reported 241.3mm, Dorchester 187.5 mm, Weymouth 178.8 mm with flooding. The
synoptic chart for this event can be found just here
So it can be seen that though relatively rare, such events as Boscastle are a part
and parcel of our climates natural extremes, that we may expect to see once every decade or so in an area like the southwest.
With grateful thanks to Dr Trevor Harley's site at http://www.personal.dundee.ac.uk/~taharley/all_extreme_weather_months.htm for some of this information.
Thanks also to Paul Blight for the technical account,
tephis and radar and Dave Jameson for general reporting.
Synoptic maps courtesy 'Wettercentrale' archives
