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Extreme Rainfall In Central England Is On The Decline

September 5, 2014

By Paul Homewood  

 

Further to my earlier post on Phil Jones’ paper on UK precipitation extremes, which showed little trend in extreme rainfall in England & Wales, I have taken a closer look at one of the regions used in the England & Wales Precipitation Series, the Central region, concentrating just on winter rainfall.

 

Region definitions for EWP

 

 

Using the England & Wales Precipitation Series, which although it dates back to 1766 only gives regional data since 1873, let’s look at the trends for winter precipitation in total.

Although rainfall last winter severely affected some parts, the Central region was only the 174 wettest on record. More significantly though, the 10-Year average is actually slightly below the mean (152mm v 156mm respectively).

 

 

image

Figure 1

 

We can also look at rainfall/rainday, the latter defined as having  >1mm of rain. The EWP Series only gives daily data going back to 1931.

 

 

Again we find daily rainfall in recent years has been pretty normal, with the 10-Year average just below the mean, 4.2mm v 4.3mm. This is certainly strong evidence that extreme rainfall days have neither become more common nor intense in recent years.

 

 

image

Figure 2

 

We can actually go one step further though, and look at the really extreme days. I have analysed all winter days with precipitation over 15mm. There have been 38 such days since 1931/32, out of a total number of raindays of 3031. This gives effectively a 99th Percentile.

Figure 3 shows the number of days with >15mm each winter, smoothed as a 10-Year running average. The biggest peak occurred from 1976 through 1980. There were other peaks in the 1950’s/60’s and again in the 1990’s.

By contrast, extreme rainfall has been notably infrequent in the last decade.

 

image

Figure 3

 

Figure 4 shows this picture better by offering the distribution of days.  

The last days with >15mm were in 2008, and neither exceeded 18mm. Contrast this with other years on record, when such days were more frequent, and much more intense. For instance, January 1961, which holds the record of 27.37mm, or the winter of 1979/80 when there were four days of more than 15mm.

 

image

Figure 4

It is plain that, in Central England at least, there is no truth in the supposition that a warmer climate will lead to more extreme rainfall.

4 Comments
  1. A C Osborn permalink
    September 5, 2014 6:27 pm

    Most people in the UK realise that our weather is controlled by that big pond to the west of us called the Atlantic, so the whole western seaboard gets a lot of rain, hence the term SouWesters for both the weather and the clothes you need for it (don’t see them much anymore).
    Whereas central areas get less rain, with the eastern seaboard getting a fair bit from the northern end of the Channel and the North sea.
    Scotland can get it from both regions so also get dumped on a lot.
    So your findings fit in pretty well with that scenario.
    I am in Swansea and our prevailing wind and weather is south westerlies, I used to live in Kent on the same logtitude and can compare the 2 sets of weather. Wales, warmer and wetter in the winter, cooler and wetter in the summer. Kent, Colder and dryer with lots of frost in the winter and hotter and dryer in the summer.

  2. September 5, 2014 8:35 pm

    Reblogged this on CraigM350.

  3. Billy Liar permalink
    September 5, 2014 10:44 pm

    I have a suspicion that the UKMO canard of more ‘extreme’ rainfall is largely based on integrating Doppler radar measurements of rainfall rates. I don’t think the ground based rainfall measurements are spatially dense enough to measure cumulo-nimbus cell rainfall except when it is, by chance, located over a rain gauge.

    Historically, therefore, ‘extreme’ rainfall will have been underestimated.

    Even if the radar measurements have been thoroughly validated, which I doubt, they will suffer the same problem as many other facets of climate science: the harder you look the more you see.

    • Ben Vorlich permalink
      September 6, 2014 7:43 am

      Similar to the tornado index in the US, increased numbers reported by modern methods of tornadoes which would have gone unnoticed in the past.

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