Are rain gauges accurate?

Before we address the question of accuracy, we want to answer a fundamental question:

How do rain gauges work?

The tipping bucket rain gauge (TBRG) consists of a funnel mounted atop a cylinder. The tapered shape collects precipitation and passes it into one of two small buckets, which balance on a pivot. After a specific amount of precipitation falls — typically 0.1mm, 0.2mm or 0.01 in — the bucket tips and an electrical signal is sent to a recorder or datalogger. This process, tips (almost all of) the water from the bucket, so the process can be repeated throughout a storm event.

Are rain gauges accurate?

Since TBRG measurements occur every time a bucket tips, very light precipitation may not get recorded. However, this amount does not represent a significant issue for many agencies monitoring rainfall.

The more significant issue is the underreporting by the traditional type of uncorrected tipping bucket rain gauges (TBRG) during periods of intense rainfall.

Experience has shown that many existing flood warning and weather monitoring networks that use uncorrected rain gauges struggle to record highly accurate data. This problem occurs for several reasons. The most significant of these is referred to as ‘loss’.

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How are rain gauges calibrated?

Technicians can use a field calibration device to checks rain gauges for accuracy. Take the portable, lightweight device into the field to conveniently run functional tests and verifications. Keep tipping bucket rain gauges at their assigned monitoring stations unless more serious repairs are required. Minimize gauge downtime.

The FCD discharges a certain volume of water into the rain gauge collector. Then, the number of tips is counted and compared with the provided calibration specifications. The tips generated when emptying the FCD water volume can be counted using an app with BlueTooth converter, by a datalogger, or manually.

What’s an alternative to rain gauges?

For the meas­urement of combined liquid and solid precipitation, weighing type precipitation gauges can be an excel­lent solution. These devices meet and exceed the updated requirements of the WMO/CIMO guideline No. 8, with an overall field accuracy of ±5%. However, the cost to deploy a network of weighing type gauges is about five times higher than deploying standard TBRGs in regions where only liquid precipitation is measured.