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Extreme Daily Rainfall In England & Wales

January 31, 2017

By Paul Homewood

 

Climate scientists frequently claim that global warming has led to more extreme rainfall, and will continue to do so.

But what does the England & Wales Precipitation series tell us about extreme daily rainfall?

Although the series dates back to 1766, we unfortunately only have daily data from 1931. Nevertheless if we plot the days when rainfall was 20mm or more, we get:

 

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http://www.metoffice.gov.uk/hadobs/hadukp/

 

In total there are 90 of these days, so about one a year on average.

By far and away the most exceptional day was 25th August 1986, when rainfall across England & Wales averaged an incredible 43mm.

As the Met Office monthly report at the time explained, this resulted from the former hurricane Charley moving across the country. (A sort of Tail End Charley, you might say!!)

 

image

http://www.metoffice.gov.uk/learning/library/archive-hidden-treasures/monthly-weather-report-1980s

 

Interestingly they also note that it was reinvigorated by contact with cold polar air.

This reminds us that it is the thermal gradient which matters.

 

image

 

 

 

 

No doubt the standout year was 2000, which recorded five days of 20mm+, all in the September – December period. However, since then things have returned back to levels regularly seen in the past.

 

As I mentioned, the daily data only begins in 1931. It is well established that the period from 1901 to 1930 was an unusually wet one, with some exceptionally wet months.

The four month period from October 1929-January 1930 was, and still is, by far the wettest on record. While August 1912, September 1918 and October 1903 were all record months in their own right.

It seems inevitable that these years and others during that period would have figured heavily on the above chart of daily rainfall.

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2 Comments
  1. January 31, 2017 5:38 pm

    “As I mentioned, the daily data only begins in 1931. It is well established that the period from 1901 to 1930 was an unusually wet one, with some exceptionally wet months.”
    As there is a strong correlation between annual rainfall and the frequency of high daily rainfall events, it is very likely that the number of such events was as high in the 1920’s and 1770’s and even higher in the 1870’s that recently.
    This is based on daily events of over 10mm but I am sure that the relationship will hold true for 20mm events.
    Annual rainfall in 1924 and 1927 was particularly high and the two highest annual rainfall figures were 1247 mm in 1768 and 1285 mm in 1872.
    Internet searches suggest that there was flooding in in those years.

  2. February 1, 2017 9:21 am

    The behaviour of the jet stream is a/the key factor.

    ‘The direction and angle of the jet stream arriving at the UK will determine what source of air (i.e. cold, dry, warm, wet, from maritime or continental sources) the UK experiences.’
    http://www.netweather.tv/index.cgi?action=jetstream-tutorial

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