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Reality Check: Extreme Rainfall Not Increasing In England & Wales

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Paul Homewood, Not A Lot Of People Know That

If I had used 1961 as the start point, there would be the clear increasing trend, which Perry identified. However, looking at the record as a whole, there is nothing unusual about recent years, and certainly nothing which justifies the claim that extreme rainfall is either becoming more common or intense.

The Met Office frequently claim that rainfall is becoming more intense in the UK. This claim stems in part from the study by Matthew Perry, “A spatial analysis of trends in the UK climate since 1914 using gridded dataset”.

This was the paper I mentioned a few days ago, with regard to sunshine hours trends. Although temperature and rainfall data is available to 1910 and before, the section on extreme rainfall only uses data since 1961. (There are other studies, but they also start from 1961, for instance here).

From that, they produce these two tables:

 image image

http://www.metoffice.gov.uk/media/pdf/q/h/UK_climate_trends.pdf

They conclude:

The increases in days of heavy rain and the greatest annual 5-days precipitation amounts suggest a tendency for an increasing likelihood for extreme heavy rainfall events.

As I have pointed out many times before, this choice of start date coincides with an unusually dry period. As flood expert, Prof Lane from Durham University states:

In terms of river flooding, the period since the early 1960s and until the late 1990s appears to be relatively flood free, especially when compared with some periods in the late 19th century and early 20th Century.

The England & Wales Precipitation Series provides daily data since 1931, so I have been able to replicate a couple of the tests that Matthew Perry made.

First, the average rain per rainday (defined as a day with >1mm), in other words, the average rainfall intensity calculated by Perry.

 image

The lowest value was recorded in the 1960’s, and the 70’s were also notably dry. The 2000’s rank only 4th (not counting the 2005-14 period, included for comparison purposes only), and at 4.9mm are bang on average for the period.

If I had used 1961 as the start point, there would be the clear increasing trend, which Perry identified. However, looking at the record as a whole, there is nothing unusual about recent years, and certainly nothing which justifies the claim that extreme rainfall is either becoming more common or intense.

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