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UK Extreme Rainfall Trends

June 7, 2021

By Paul Homewood




In March a Safety Review Report was published regarding UK reservoirs:






In the section on the potential impact of climate change, it included these graphs from the Met Office, illustrating trends in extreme rainfall:






The second (ie “right”) panel is statistically meaningless. It is based on a station mix which has constantly changed during the period. We know, for instance, that the Met Office have introduced many mountain sites in recent years, using Environment Agency automated meters. By nature these are more likely to record higher rainfall totals. For the exercise to be meaningful, it would have to based on a fixed number of stations with continuous data. There are many of these, with the added advantage of longer records too. I cannot understand why the Met Office failed to do so.


As for the first graph, the real measure of extreme daily rainfall is the 99% percentile, typically an event that happens once or twice a year, rather than the 95% percentile. The 99% percentile shows very little change over the period, peaking in 2000 and 2002.

We can repeat the exercise using data at Oxford back to 1900, and this confirms that little has changed in that time. Interestingly the worst years were 1927 and 1949.





Oxford is pretty representative of the southern half of England, but there may be be regional differences at play. However a quick look at some of the other long running stations elsewhere in the country appear to show no significant trends either.








Just for completeness sake, below is the 95% percentile graph for Oxford. Clearly nothing of concern here either when looked at over the full period since 1900, rather than the Met Office’s truncated post 1960 chart.



  1. June 7, 2021 7:51 pm

    By definition few people wanted to live in the mountainous and wettest areas of the country and those that did would not be interested in taking daily accurate records whilst being soaked.

    As Paul says, for this to be meaningful you have to have the same stations recording over a long time by someone who knew what they were doing.

    At nearby Dawlish when Brunel was building the Great Western Railway there were two people locally taking rainfall measurements.

    One was a senior engineer working on the railroad.

    The other was the bored well to do wife of a wealthy land owner famous for her social life.

    It is doubtful their records would coincide

  2. George Herraghty permalink
    June 7, 2021 7:55 pm

    Extreme Rainfall?
    The Great Flood of moray, 1829. The ‘Muckle Spate’ saw the water rise to one foot under the central span of Telford’s famous Craigellachie Bridge.
    Rabbits and hares were spotted sitting on logs 10 miles out at sea from passing fishing boats.
    Nothing new.

  3. mikewaite permalink
    June 7, 2021 8:22 pm

    This paper might be of interest :

    Click to access hess-21-1631-2017.pdf

    High-magnitude flooding across Britain since AD 1750

    “Abstract.The last decade has witnessed severe flooding across much of the globe, but have these floods really been exceptional ————-
    Here, we show how historical records from Britain have improved understanding of high-magnitude floods, by examining past spatial and temporal variability. The findings identify that whilst recent floods are notable, several comparable periods of increased flooding are identifiable historically, with periods of greater frequency(flood-rich periods). Statistically significant relationships be-tween the British flood index, the Atlantic Meridional Oscil-lation and the North Atlantic Oscillation Index are identified.The use of historical records identifies that the largest floods often transcend single catchments affecting regions and that the current flood-rich period is not unprecedented”. (open access)

    I am sure that some here , if not already aware of the paper, would be interested in one of their conclusions :

    “The principal findings of this work are that of the strong correlations between flood-rich/flood-poor phases and solarmagnetic activity, AMO and NAOI, indicating a clear driver for flooding patterns across Britain”.

    I have not , as I should do, checked the later citation references to this paper to see how well or not it was received by the authors’ fellow scientists .

  4. Mack permalink
    June 7, 2021 10:40 pm

    I note that the learned professor, who authored this report, hopes that modelling by the Environment Agency might assist in addressing any future weather issues impacting reservoirs caused by the ‘non stationarity of climate’. Stock up on arm bands and rubber rings folks, we’re doomed.

  5. wisewullie permalink
    June 7, 2021 11:00 pm

    “I cannot understand why the Met Office failed to do so” Oh yes you can.

  6. bobn permalink
    June 8, 2021 12:05 am

    Ludicrous that the paper looks for trends over such a short time period (60yrs is 2 data points). As we know climate follows a series of long and short cycles. Anything less than 120yrs is ridiculous.

  7. Martin Brumby permalink
    June 8, 2021 6:25 am

    Don’t forget that reservoir dam spillways are designed to pass the 10,000 year flood.

    A pity, then, that Noah’s data is a bit, ahem, patchy.

    I’m sure the good Professor was envigorated by his little session of shroud waving.

  8. cookers52 permalink
    June 8, 2021 6:32 am

    I have some sympathy with the dam regulation reports author.

    He was given the unenviable task of explaining away lack of government oversight as a direct cause of the risk imposed on the public, from the inadequate dam regulation. So including a few dodgy scary climate change potential hazards is sort of expected.

    Parliament, as deliberate strategy, has developed legislation that has enabled self regulation to become the norm in many areas of public safety, and not surprisingly there are failures in regulation and people get harmed. Grenfell tower is an example of this failed strategy.

    The current political paradigm is that government is not best placed to look after public safety, so politicians only develop strategies and leave the implementation to others.

    However politicians believe that many successful strategies fail in implementation!

  9. Chaswarnertoo permalink
    June 8, 2021 9:24 am

    There is no extreme rainfall. Just brainless management.

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