Is The Honister Rain Gauge Accurate?
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
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.
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?
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.
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:
This ludicrous statement is wrong on so many levels.