Somerset Floods Update
By Paul Homewood
As the waters thankfully begin to recede on the Somerset Levels, it is time to take stock of the last three months.
After a drier than normal November, the rain began falling in earnest in the second week of December, and only began to abate in towards the end of February.
Met Office regional statistics for SW England & S Wales extend back to 1910, and according to these, the December to February period just ended recorded the highest precipitation on record, with 670.6mm. However, this does not tell the whole story, since other years have recorded higher 3-month totals, as Table 1 shows.
|Nov 1929 to Jan 1930||812.2|
|Oct 2000 to Dec 2000||700.8|
|Dec 2013 to Feb 2014||670.6|
Altogether, there have been six winters including this one, where precipitation has exceeded 600mm over a 3-month period. As well as the three above, there has also been 1959/60, 1960/61 and 1989/90. It could therefore be argued that what we have seen this year is a once every 15-20 year event.
While this year’s heavy rain was spread over three months, it should be borne in mind that in other years the unusually wet weather extended for four consecutive months.
The average monthly rate from October 1929 to January 1930 was 251mm, which was more than this winter’s three month average of 223mm.
|Oct 1929 to Jan 1930||1005.4|
|Oct 1960 to Jan 1961||778.2|
|Oct 2000 to Jan 2001||820.8|
|Nov 2013 to Feb 2014||777.8|
Local Data For Somerset.
Is the regional data representative for Somerset itself?
Unfortunately the Met Office data for the local station at Yeovilton only dates back to 1964
However, the old British Rainfall publications have a wealth of data, until they were ceased in 1991. (I’m not sure what this says about the Met Office’s transparency!). These publications give us monthly rainfall data for several stations in Somerset, including Street, which is within about 15 miles of Yeovilton. They are both low level stations, so we should be able to directly compare them.
(Also, the 1961 British Rainfall shows that annual rainfall for Street and Yeovil was 28.1 and 28.6 inches, respectively, so Street appears to be a reasonable proxy for Yeovilton.)
Table 3 compares rainfall at Street in 1929/30, with this winter at Yeovilton.
|Oct 1929||119||Nov 2013||57|
|4-Month Total||543||4-Month Total||473|
|July 1960||128||July 2013||40|
|Jan 1961||112||Jan 2014||166|
|8-Month Total||904||8-Month Total||710|
Okehampton Street, Exeter, October 1960
Long Term Trends
Finally, let’s have a look at the record since 1910, to see if there is any trend towards increasing rainfall during the heaviest rainfall months of September through February.
This year’s total ranks third behind 1929/30 and 2001/01, but the 10-Year trend has actually been falling during the last decade, and at 742mm is close to the mean of 733mm.
Heavy rainfall in Somerset this winter has been unusual for its duration of the best part of three months, but nevertheless is by no means unprecedented. As with the country as a whole, rainfall in 1929/30 was both much more intense and longer lasting. Another four years had comparable episodes to this winter.
Meanwhile, there is no evidence that winters are becoming wetter.
The bottom line is that the flooding on the Somerset Levels this year cannot be blamed on climate change.
1) Regional data
2) Data for Yeovilton