Raingauge comparative trials

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Raingauge comparative trials

Postby Stephen Burt » 2013 May 20, 15:50

Over the last few months I have been running a comparison of the low-cost CoCoRaHS plastic raingauge against the UK/Ireland standard 'five-inch' copper gauge. CoCoRaHS http://www.cocorahs.org (an abbreviation for ‘Community Collaborative Rain, Hail and Snow Network’) is a North American grassroots volunteer network of backyard weather observers of all ages and backgrounds working together to measure and map precipitation (rain, hail and snow) in their local communities. By using low-cost measurement tools, stressing training and education, and utilising an interactive Web-site, the organisation aims to provide high-quality data for natural resource, education and research applications. The only requirements to join are an enthusiasm for watching and reporting weather conditions and a desire to learn more about how weather can affect and impact our lives (oh, and living in the United States or Canada ... !)

Over the last few years the CoCoRaHS network has grown rapidly, to the point where there are now more CoCoRaHS gauges and observers than the 'official' NOAA/National Weather Service network, today numbering more than 15,000 in all. Now that the gauge is becoming available in Europe, it's appropriate to assess how well it compares against standard raingauges.

The bottom line is that it performed very well - within about 2 per cent of an adjacent five-inch gauge (at a single site in central southern England). It would therefore seem to be an attractive inexpensive alternative to the standard copper gauge, as it is about a fifth of the price. It's particularly relevant to those members with an automatic weather station who do not have an independent means of measuring rainfall, as the tipping bucket unit in most consumer AWSs, including those from Davis Instruments, can be very inaccurate.

The full review is available here: http://measuringtheweather.com/equipment-reviews/ and a photograph of the gauge itself is (hopefully) attached below.

SB
Attachments
2012 08 14 - 0909z - 007 (240 x 360).jpg
2012 08 14 - 0909z - 007 (240 x 360).jpg (16.75 KiB) Viewed 2326 times
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Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
Stephen Burt
 
Posts: 247
Joined: 2011 Dec 02, 19:36
Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading

Re: Raingauge comparative trials

Postby Richard Hunt » 2013 May 21, 16:23

I am pleased you have done this review as I have a "CM1016 - Professional Manual Rain Gauge" from Metcheck which seems to all intents and purposes exactly the same as the US CoCoRaHS gauge. The dimensions are exactly the same, the only difference being mine has a green funnel instead of the totally clear one used on the US gauge.

I have had this installed at the same height (or thereabouts) as your gauge on a fence post for just over two years and I find it suits my needs fine. I don't have the open spaces you have but I have it in the best position I can.

I agree a tapered measuring cylinder would help for trace amounts, but other than that the gauge has been faultless.

Is they any difference between the US and Metcheck gauges?.

Very intresting review, enjoyed reading it.
COL Station: 25020.

Watson W-8681 AWS. Standard Stevenson Screen. Maximum and Minimum screen thermometers. Grass minimum thermometer.
5" Copper standard rain gauge. Roof mounted annemometer.
Richard Hunt
 
Posts: 374
Joined: 2012 Jan 27, 19:23
Location: Hornsea, East Yorkshire. 10m AMSL

Re: Raingauge comparative trials

Postby Stephen Burt » 2013 Jul 02, 16:19

I've now updated the comparison of the CoCoRaHS plastic raingauge vs the standard five-inch model to include May and June results, thus completing a full 12 month overlap at my site in Berkshire.

The results differ from the interim version only slightly - the CoCoRaHS gauge recorded within 2% of the standard gauge over the 12 months. Full results are in the PDF, which can be downloaded from

http://measuringtheweather.com/equipment-reviews/

On the basis of the comparison trial, the CoCoRaHS gauge can be strongly recommended for UK/Ireland observers where budget considerations do not permit consideration of a standard ‘five-inch’ copper raingauge. Although the results from the CoCoRaHS gauge cannot be accepted as fully comparable with the official standard, this analysis has shown that differences over a lengthy comparison period, measured daily, were small - a very acceptable 2 per cent at the comparison site, although it is likely that losses would be greater in areas with a higher frequency of strong winds and wind-driven rain than central southern England.

This gauge is particularly recommended for owners of automatic weather stations whose only precipitation measurements come from the built-in tipping-bucket raingauge within such systems. Experience has shown that the ‘out-of-the-box’ calibration on such units can be 20 per cent or more in error, while simple blockages may quickly destroy the reliability and continuity of rainfall records. A fixed manual raingauge installed on the same site will invariably provide both more accurate and more reliable measurement of absolute precipitation totals, help pinpoint any shortcomings in instrument calibration and identify any periods of instrumental failure or funnel blockages.

The CoCoRaHS gauge will shortly be de-installed and moved to a wetter and windier site in the north of England, and the results from that site will be appended to the review once a further 12 months daily observations have been obtained.

Thanks to John Dann of Prodata, who loaned the CoCoRaHS gauge for this independent review - see http://shop.weatherstations.co.uk/cocor ... -802-p.asp

SB
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Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
Stephen Burt
 
Posts: 247
Joined: 2011 Dec 02, 19:36
Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading


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