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Is The Honister Rain Gauge Accurate?

December 9, 2015

By Paul Homewood   

  

The Old Bloke left a very interesting comment on the “record” rainfall total at Honister, where the rain gauge is operated by the Environment Agency:

 

So, was it a record or wasn’t it? The claim is that in Honister, Cumbria, an Environment Agency rain gauge recorded a record in the U.K for an amount of rainfall collected in 24 hours, that being 341mm. Or did it? How many of us know that the Environment Agency use different gauges to that of the Met Office and that the Environment Agency rain gauges do not conform to the “Standard” W.M.O. 5″ collection tube? Well, I did. I also know that at the last review, the E.A. gauges, mainly “tipping bucket” types are known to record spurious data as the method of collection and measuring has given rise to incorrect data. The funnel to collect the rainfall is not the standard 5″ as in the Met Office gauges but can be up to 12″ for the E.A. ones. The E.A. gathering can also be greatly affected by wind and to a lesser degree by temperature. The E.A. know that their gauges cannot be relied upon and as such ‘adjustments’ have to be made.
I have enclosed some important links for all of the forum members and trust that they are read.

 
The first is a photo of the E.A. device at Honister
http://www.geograph.org.uk/more.php?id=2666377
The rain gauge is the white “toilet” bowl in the back ground and this picture can be enlarged by clicking on it.

 

Next is the problems pertaining to the “tipping bucket” gauges as used by the E.A.
http://www.emltd.net/pdf/Evaluation%20of%20Tipping%20Bucket%20Rain%20Gauge%20Performance%20and%20Data%20Quality.pdf

 

And third is the Met Office requirement as stipulated by the “standard” rain gauge which is commonly used throughout the world and regulated by the W.M.O.

[An ordinary funnel-type raingauge has been in use for all manual measurements since the earliest days of observing. The design has varied over the years but today the Met Office strongly encourages conformity in order to maximise comparability of readings across the network. The standard design has a rim of diameter 5 in (127 mm) standing 12 in (30 cm) above the ground. Raingauges based on the standard design are adapted to meet specific needs; there is a version having a capacity to hold a large volume of rain which is used in remote sites where readings may only be taken once a month. Exposure of the gauge should be on open ground distant from the effects of sheltering objects. At a few windy sites, established a number of years ago, there may be a surrounding turf wall of diameter 3 m and height 30 cm which shields the gauge from the extreme effects of strong winds. Systematic differences as large as 12% have been noted between an unsheltered gauge and one within a turf wall. It is not the present practice to build turf walls at new station]

To repeat, the standard Met Office gauge has a collecting neck of just 5″ whereas the E.A. in the photo above has a 12″ bowl leading to a collecting chamber. Is it no wonder that a record was set if the collecting bowl was nearly 3 times the size?

http://www.metoffice.gov.uk/media/pdf/0/p/OH_Chapter9.pdf 

 

 

It is worth noting that the Met Office still have not officially logged the Honister rainfall as a record. (I do seem to recall they declared the “record” temperature on Heathrow runway within minutes in July).

It remains to be seen whether they will confirm the Honister one.

 

image

http://www.metoffice.gov.uk/public/weather/climate-extremes/#?tab=climateExtremes

 

In a way, none of this would matter if it was just an entry in the Guinness Book of Records. But it is not. This one rain gauge has led to media claims, such as this one in the Telegraph:

 

image

http://www.telegraph.co.uk/news/weather/12036138/Cumbrian-floods-cancelled-flood-defence-schemes-may-have-added-to-misery.html

 

This ludicrous statement is wrong on so many levels.

18 Comments leave one →
  1. December 9, 2015 2:56 pm

    ” … the standard Met Office gauge has a collecting neck of just 5″ whereas the E.A. in the photo above has a 12″ bowl leading to a collecting chamber. Is it no wonder that a record was set if the collecting bowl was nearly 3 times the size?”

    Only if the depth-measurement was taken in a chamber having a diameter of 5″. Surely the diameters of collecting neck & depth-measurement chambers should simply be identical, or, mathematically related.

    • David Richardson permalink
      December 9, 2015 6:25 pm

      True at the one level Joe, but in a windy regime it might be a factor. The reason for exposure rules for rainguages is to avoid false readings from very heavy precipitation bouncing off the surrounding ground into the guage. Whatever way you do it there must also be scope for rain bouncing out of the guage in heavy, windy conditions.

      Someone more current than I with practice today can tell us, but I expect that tipping bucket guages {similar to the Honister guage} are used at Met Office sites giving 0.2 mm clicks and hourly readings. This is handy as it gives rainfall rate as well as amount. I assume that a 5 inch guage (simply a sharp edged funnel draining direct to a bottle) is read at least once a day – 0900 GMT? . Obviously if the site is unmanned there may be no 5 inch guage as this requires an observer – rare as hens teeth these days I would guess. I am not sure how much effort goes into reconciling both guages where they exist.

  2. December 9, 2015 3:14 pm

    Paul, There’s a very early retweet by EA of tweet of a higher measurement by one of their guys

    “‏@TobyWillisonEA Dec 5
    Provisional figures from a rain gauge in Honister #Cumbria shows 352mm of rain fell in 24hrs, if verified this would be a UK record”

    I saw also tweets of 340, the fig mentioned first by BBC (340 was also mentioned in 2009 so you’d need 341 fro a record maybe ? tho the 2009 record was mentioned as 316mm) seemed to me the figs were murky.
    (I Wonder is a legend of 341 could come from mis-reading of 314)
    Later the Guardian was the first to print 341mm claim but GODD ON THEM for contexting it

    The Met Office’s confirmed 48-hour figures.. were more modest. .. Shap 262.6mm, Keswick 178mm and Blencathra 175mm..said .some parts of the county might have experienced 300mm of rainfall

    #1 Skeptics have to acknowledge it was a pretty big rain.

    #2 Media people who run around shouting about an unconfirmed anomoalistic measurement at one place are really showing they’re low class Honister on its own should not matter, but rather indications of a trend across a number of guages.

  3. xmetman permalink
    December 9, 2015 3:16 pm

    Paul

    Although this blog I’ve put together is only loosely connected to your post, I don’t have your email address and thought that you might like to read it:

    https://xmetman.wordpress.com/2015/12/09/seven-times-more-likely/

    Bruce.

  4. December 9, 2015 5:55 pm

    What we need is a media jingo index.

    The number of times that climate change has been claimed to be proved by the awful flooding (and now lakes drying-up in Arica as a BBC theme) is beyond belief. Very similar to the Heathrow fiasco.

    None of the reports contained any balance or allowed for other opinions: this is the level of brainwashing that the UK’s media now exemplify: the ministry of truth even down to re-writing temperature history!

    Doomed, we’re all doomed.

    • Anoneumouse permalink
      December 9, 2015 9:35 pm

      you mean a sligoism

  5. December 9, 2015 7:57 pm

    Um, surely the size of the container doesn’t matter, X cm of rain means any (flat-bottomed) container will get a water depth of X cm, regardless of area?

    • Anoneumouse permalink
      December 9, 2015 9:37 pm

      Have you ever tried to piss into an empty bottle from 5ft away.

  6. Ted permalink
    December 9, 2015 8:14 pm

    “Um, surely the size of the container doesn’t matter, X cm of rain means any (flat-bottomed) container will get a water depth of X cm, regardless of area?”

    It depends. Might not matter in windless conditions. Where there is wind though this affects the amount of rain collected. So for the sake of standardising measurements the same design of gauge should ideally be used.

    A history of rain gauges is at

    http://www.rmets.org/sites/default/files/pdf/presentation/20100417-strangeways.pdf

    • December 10, 2015 7:51 am

      OK, wind will spread rain over a larger surface area, but any gauge will record the amount that falls at its location, if it didn’t where would the missing rain go (I’m thinking here of a carpet of gauges, one real one, surrounded by hypothetical ones, no gaps).

  7. Anoneumouse permalink
    December 9, 2015 9:18 pm

    We’ll keep a crapper on the hillside

  8. December 9, 2015 9:24 pm

    Paul: forgive me if someone has asked this already, but this question has been nagging me ever since the Honister story broke.

    Do you know what the readings were for Seathwaite and other neighbouring sites at the crucial time? Or what equipment they use? Or is such information not made available to ordinary mortals by DEFRA and the Met Office?

    • December 9, 2015 9:54 pm

      I’ve asked the Met Office about Sleathwaite. I assume it must be less than the other examples they gave on their blog, which would put it well below 200mm for 48 hours.

  9. December 10, 2015 9:45 am

    Thanks Paul. What you say, and the Met Office’s apparent failure to confirm the record, really does look pretty bad.

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