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Extreme Rainfall In Sheffield Shows Little Trend

September 26, 2014

By Paul Homewood

 

image

http://www.metoffice.gov.uk/media/pdf/4/8/Drivers_and_impacts_of_seasonal_weather_in_the_UK.pdf

 

The UK Met Office keep banging the drum about how extreme rainfall is on the increase. In their March publication, “Too Hot, Too Cold, Too Wet, Too Dry”, they included the above graph, purporting to show that what was a 1 in 125 day event in the 1960’s and 70’s was now a 1 in 85 event in the UK.

 

I pointed out at the time that the 1960’s and 70’s were an unusually dry period, as explained by Professor Stuart Lane of Durham University, and suggested that a longer perspective would not show such trends.

Replicating the Met Office study, I showed that there was indeed little trend of any sort, using daily data at Oxford and Bradford.

I have now managed to obtain daily rainfall for Sheffield from the observatory there, which goes back to 1883, so can now repeat the exercise over a longer period. Sheffield, where I live, is in South Yorkshire, so is in a fairly central position of the country.

The graph below plots the number of days each year when precipitation exceeded 22mm. This is equivalent to the 99th percentile, i.e.a 1 in 100 year event, as used in the Met Office chart.

 

image

 

The peak in the exceptionally wet year of 2012 stands out, but otherwise there appears to be little trend. The dry period for much of the 1960’s and 70’s stands out, and any analysis beginning then would suggest an increasing trend of extreme rainfall days, as the Met Office report. However, looking further back, we can see that this supposed trend disappears. The current 5-yr trend is actually pretty much normal.

It is noticeable though that heavy rainfall days were less common in the early part of the record up to around 1900. These extreme days seem to come in clusters, and these seem to have peaked in 1941, and again in 2002.

 

Incidentally, the wettest day on record was 15th July 1973, when 119.2mm fell. The highest recorded since was 88.2mm in 2007.

 

 

Source

Data is from Weston Park Weather Station, Museums Sheffield .

http://www.museums-sheffield.org.uk/museums/weston-park/home

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7 Comments
  1. September 26, 2014 8:38 pm

    @Paul
    I would be interested in looking at the original Sheffield rainfall record,
    if you can give it to me?
    (preferably excel)
    I have been finding interesting patterns when looking at the Hale-Nicholson cycles, especially 4 cycles in a row.
    (sofar I have analysed Potchefstroom South Africa and Wellington NZ)

    One would naturally expect a link between temperatures [i.e. global warming and -cooling] and rainfall.
    http://blogs.24.com/henryp/files/2013/02/henryspooltableNEWc.pdf

  2. September 27, 2014 1:54 pm

    Here is what I mean

  3. September 27, 2014 2:02 pm

    oops
    something went wrong with the link
    let me try again
    http://tinypic.com/view.php?pic=2ng4lft&s=8#.VCbC82eSzJo

  4. September 27, 2014 2:13 pm

    Well, after three times I got it right. Not too bad for an old man like me…
    Note that the relationship only holds for the period 1927-2015.
    So, the backward and forward projection is not going to be correct. It is just illustration.
    I expect dead end stop occurred in 1927 and will occur again in 2015-2016.
    That means rainfall will go the opposite direction as what you would think,
    i.e.
    1904-1927 ca. 587
    1927-1950 611.7
    1951-1971 587
    1972-1995 596.1
    1996-2013 641.2
    2017-2039 ca. 596

    It is nice to know for weather forecasters.

    @Paul

    Could you just check for what we can expect in Sheffield?
    (Using the average annual rainfall for the periods indicated).

  5. manicbeancounter permalink
    September 27, 2014 9:48 pm

    One small observation. In the last century there were two warming phases. One ended with a peak around 1940-1944 and the other 1998. Two of the peaks in the five-year moving average of rainfall are coincident with these temperature peaks. Another peak is just after the start of the resumption of warming in the late 1970s.
    However, there is no such similar pattern for Oxford and Bradford. It is very easy to see patterns in limited data. It is only by looking at data over long periods and a number of different places that we can greater confidence in those patterns through corroborative evidence. What is easier to confirm by looking at additional data sets is that the apparent consistency of the data sets is just by chance.

  6. September 29, 2014 8:45 am

    I ran some statistics control charts [ to show if a process is in or out of control ] on our wet weather, check them out on my website and and see what you think.

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