Somerset Floods – Rainfall Was Not Unprecedented, So Why Did The Levels Flood?

By Paul Homewood     

 

 

I mentioned about progress on the Somerset Flood Action Plan last week. We have not had any rainfall anywhere near as much as the winter of 2013/14 since, so it is difficult to say whether the Plan will totally solve flooding problems.

But a look at the local rainfall records reveals that the area has had similar or greater amounts of rain as 2013/14 on several occasions in the recent past.

First though a quick recap.

 

 

The floods in Somerset two years ago followed about a month of heavy rain. In other words, they were not flash floods. The rain began in earnest on Dec 5th, following a dry November, when rainfall was more than 40% below average.

By early January, there was talk of “unprecedented” flooding, which progressively became worse as heavy rain continued through January, peaking in early February.

 

The Met Office publish weather data from Yeovilton, the RAF base 5 miles north of Yeovil and close to the Somerset Levels. This only has data back to 1964, so unfortunately misses some of the really wet periods in earlier decades.

 

 

The rainfall data in 2013/14 was:

 

	mm
Nov 2013	42.9
Dec 2013	121.4
Jan 2014	166.4
Feb 2014	131.2

 

 

As we can see from the Top 20 analysis below, even the January figure was not a record, having been beaten in October 1976 and November 2002, and effectively tied in December 1989.

I have only included the “Winter Six Months”, from October to March, on the basis that heavy summer rainfall is quickly absorbed, evaporated or carried away with a low water table and river levels.

 

 

http://www.metoffice.gov.uk/pub/data/weather/uk/climate/stationdata/yeoviltondata.txt

 

Bear in mind that we saw “unprecedented” floods even after the December rainfall of 121.4mm, which was certainly not an unusually high amount.

Of course, heavy rainfall continued throughout January, so are the two-month rainfall numbers in any way unprecedented? In fact, not.

The wettest two month spell was Sep/Oct 1976, when 339mm fell, compared to 289mm in Dec/Jan 2014. Of course, after the dry summer of 1976, the flooding potential may have been reduced in that year. But we also find rainfall of 335mm in Oct/Nov 2002, a time of year when Somerset has often suffered flooding.

But perhaps most comparable was Dec 1989/Jan 1990, when 270mm fell, nearly as much as two years ago. If we compare the rainfall series for the two, we get close similarities:

 

mm	1989/90	2013/14
November	48	43
December	166	121
January	104	166
February	133	131

 

According to the Met Office monthly report for December 1989, the weather was largely dry up to the 11th, when a series of storms set in, bringing the worst flooding in years at Plymouth on the 16th.

In other words, the rainfall in December 1989 was much more intense than we had in December 2013, which brought “unprecedented” floods to the Somerset Levels. Into January and February, we find that the cumulative rainfall was only marginally greater in 2014.

 

The Somerset Levels have always been prone to flooding, and certainly would not have escaped in 1990. However, it is evident that the flooding problems of 2013/14 were much more severe than would have justified by the rainfall amounts on their own.

Of course, in 1990 the rivers were still being dredged and the pumping stations kept operational.

Either way, it is clear that “climate change” had nothing to do with the floods at all.

One further question – why did we hear none of this at the time from the Met Office?