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New Paper Finds No Increase In Extreme Rainfall In England

September 3, 2014

By Paul Homewood

  

This paper, first published last November, “Analysis of UK precipitation extremes derived from Met Office gridded data”, by Jones and Simpson seems to have slipped below the radar.

 

ABSTRACT

In Simpson and Jones (2012) we introduced new, homogenized UK national and regional rainfall series derived from 5 km gridded daily and monthly precipitation data. The monthly series were extended back to 1766 for monthly England and Wales (EW) precipitation, to 1873 for monthly values for each of the five EW sub-regions, and to 1931 for daily values in all regions. Using data from those series, this paper provides analysis of how mean precipitation totals and extremes have changed over the respective periods. The results showed statistically significant upward trends in mean and extreme winter, spring and autumn precipitation for some Scottish regions, but trends over England and Wales were mostly insignificant, though England and Wales had a significant increase in winter precipitation over 1766–2011. The trend in summer precipitation over 1931–2011 has been statistically insignificant, though with a significant long-term downward trend for England and Wales over 1766–2011. Prior observations of a trend towards drier summers and wetter winters have been complicated by a recent succession of wet summers and dry winters. Many of the observed changes in seasonal precipitation totals are most likely associated with changes in the North Atlantic Oscillation.

 

 

Although I have not looked at Scotland separately, it does not surprise me that extreme precipitation has been increasing there. We know that rainfall totals have, and logic suggests some of this would fall as heavy rain.

What is more interesting, though, is that there has been little trend in England & Wales, either in seasonal or extreme precipitation. This rather confirms what my analysis has already shown, for instance here.

 

It is worth looking at a couple of the graphs to give the flavour of the paper.

The first is the wet-day index, i.e. the average rainfall per rainday, and the second plots the trend of the 90th percentile.

 

 

 image

 

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Both graphs follow similar patterns; notable is the spike in both plots for winter precipitation in the 1990’s, which the authors find are at least partially associated with “a strongly positive NAO”.

Current levels seem to be back to where they were in the 1930’s, as far as winter precipitation is concerned. As I have speculated before, given that winter precipitation in England was at its highest in the 1910’s, it appears likely that extreme rainfall would also have been more common then.

 

 image

http://www.metoffice.gov.uk/climate/uk/summaries/actualmonthly

 

 

Finally, it is worth repeating what is said about seasonal trends.

Prior observations of a trend towards drier summers and wetter winters have been complicated by a recent succession of wet summers and dry winters.

 

And they conclude:

The observed trends in UK precipitation are mostly consistent with the projections from climate models, with evidence of a trend towards wetter winters (especially in Scotland) and drier summers. The trends in mean precipitation have generally been less significant than the trends in extreme precipitation, and many years since 2000 have bucked the trend towards wetter winters and drier summers

 

As they admit, the trend towards drier winters and wetter summers in recent years is opposite to what the models were predicting.

 

I plan to do some more detailed analysis on this topic in the next day or so.

2 Comments
  1. September 3, 2014 9:44 pm

    so all the hype emanating from the same old suspect media sources and the proponents of catastrophic climate, surrounding last winter’s ‘extreme rainfall’, leading to flooding in the Somerset levels, where in fact predominately caused by a failure of the Environment Agency’s deliberate policy to reduce or cattail the historical dredging of rivers,

    This ‘extreme unprecedented rainfall event’ was even cited as evidence at a wind farm appeal by the appellants in January this year, as justification for their ridiculous planning application,… wait for it…. for their wind farm, comprising of a turbine positioned in an relatively small overflow flood reservoir adjacent to a canal and the others located in the adjacent flood plain, where the 1,000 tonnes of concrete required per turbine foundation and infrastructure, would have seriously changed the ground’s permeability to absorb the extra run off water..

    Incidentally the overflow reservoir is under the Environment Agency’s management & control and they thought it was an excellent proposal…

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