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Are Heavy Rainfalls On The Increase In The UK?

March 2, 2012

By Paul Homewood

 

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It is often claimed that global warming is leading to an increase in the number and/or intensity of extreme rain events. Is there any evidence of this in the UK?

We have already seen that rainfall trends in England and Wales are pretty much flat, with no significant trends to either more or less rainfall either seasonally or regionally (see here). But are the overall figures hiding higher daily rainfall totals?

In a previous exercise, I looked at four sites which give a fair regional representation :-

Heathrow – South East

Shawbury – Midlands

Aberporth – Wales and the West

Bradford – North

I have obtained the daily rainfall data from the Met Office for these four stations, going back to 1951, so let’s have a look at the trends for Heathrow and Bradford. (I’ll post up the other two tomorrow).

Heathrow

I have filtered the 50 days with the most rainfall for 1951-2010 and the distribution by decade looks like this.

 

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There were only four days in the latest decade out of the top 50. Could these days, though, have experienced more intense rainfall than previous decades? The following graph shows the distribution of each of the 50 days.

 

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Quite clearly the trend at Heathrow is less intense rainfall. Bradford, however presents a drastic contrast.

 

Bradford

 

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Not much changing on the number of days, but the distribution tells a different story.

 

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The heaviest rainfall was in 1986 and this seems to have marked a change to heavier rainfalls . (It is worth noting here, as the graph does not make it clear, that the data goes up to 2011 and there have been no top 50 days in 2009,2010 or 2011).

 

Conclusions?

Are there regional factors at play which explain the different trends? Is it just weather? Will the trends continue?

A look at the other two sites will, I believe, put these trends into much clearer perspective.

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