How accurate are rain gauges? You may be asking this question if you are currently thinking of buying a backyard rain gauge to keep an eye on the changing weather.
No doubt, rainfall monitoring is essential for farmers.
Because of this, most farms have both a manual rain gauge and a Rainwise weather station wired into NEWA.
It is a good idea to get into the habit of checking your weather station data against readings from a manual rain gauge.
But, really, how accurate are backyard rain gauges?
The accuracy of backyard rain gauges depends on the type and brand you use, but some are quite accurate, displaying rain totals down to 0.01 of an inch.
How Accurate are Rain Gauges?
You can find many different types and brands of rain gauges, which vary significantly in accuracy.
Among the most accurate rain gauges are those that can display rain totals down to 0.01.
It indicates that the rain gauge can accurately record and report rainfall down to the hundredth of an inch.
This precision is useful for determining the total amount of rain that has fallen at a given place.
Fact: The rain gauge's ability to deliver precise measurements is handy in applications ranging from weather forecasting and agricultural planning to flood monitoring and more.
How Accurate Are Different Types of Rain Gauges?
When speaking of accuracy, you first need to consider the type of rain gauge you are going to use.
The most commonly used are:
- The standard rain gauges
- The weighing rain gauges
- Tipping bucket rain gauges
Which one of these is going to be the most accurate? Let’s talk more about it.
The Standard Rain Gauges
A standard or funnel rain gauge requires manual recording of precipitation.
Such rain gauges have a funnel-shaped collector at the end which is a measuring tube.
Since the collector’s surface area is 10 times that of the tube, the rain gauge effectively acts as a 10-fold magnifier.
This method of magnifying the rain makes measurements accurate within a hundredth of an inch.
A gauge’s outer casing catches readings too high for the tube, allowing the recorder to refill the tube by pouring out the excess liquid.
The Weighing Rain Gauge
For climatological purposes, a universal weighing rain gauge is usually a superior option.
It is a more useful option because more precipitation is able to enter the gauge thanks to a vacuum that counteracts the effects of wind.
The weighing mechanism at the collector’s base allows for highly accurate measurements of both depth and time, making these gauges ideal for monitoring rainfall amounts.
Fact: The weighing rain gauges are popular because of their accuracy and recording process, which is very similar to traditional tipping bucket gauges.
Tipping Bucket Rain Gauges
When it comes to statistical accuracy, the 8-inch tipping bucket rain gauges surpass NWS standards.
The water flows through the collector’s screen and into the emptying bucket below.
The water slowly fills the bucket and as it teeters back and forth, it empties out of one side first, much like a teeter-totter.
A reed switch is set to register 0.01 inch (=0.25 mm) of rain records each time the tipping bucket located beneath the black collector moves.
Because of its low surface tension, the plastic used to make the tipping bucket allows the gathered rain to quickly and completely drain off.
Is the Traditional Tipping Bucket Gauge the Most Accurate?
It is true that traditional tipping bucket gauges are popular because of their accuracy, but they are not without disadvantages.
One issue is that they become ineffective or stop working entirely when frost is present.
Another issue is that they do not catch enough water at times of excessive downpours, such as when more than 1.5 inches of rainfall in an hour.
It happens when the tipping arm fails to maintain the rate at which water is flowing into the bucket.
Because of this, rainfall totals may cover a longer period than the rain really fell.
The Idea of Going with Electronic Tipping Bucket Rain Gauges
The electronic tipping bucket rain gauge eliminates the need to manually check, empty, and reset the instrument after each rainfall.
Manufacturer calibrations for these automated gauges are not always accurate, especially after a couple of years of use.
Tipping bucket rain gauges from popular brands are accurate to within 2% at a rate of 1.5″ per hour.
An Important Consideration
There should not be more than a 2% discrepancy between the data from the manual rain gauge and that from the tipping bucket rain gauge for the same time period.
Errors in tipping bucket calibration might range from 5% to 10%.
There is probably a clog in the tipping bucket collector if it is collecting less than 90% of what your manual gauge is gathering.
Fact: The accuracy of plastic rain gauges with a 4-inch diameter top aperture is very high but can be expensive.
How to Confirm Your Rain Gauge is Accurate?
Calibration testing for a rain gauge is important yet easy to do.
However, it is also simple to introduce complications, such as passing off simulated data as real data.
Data loggers often require only a one-time setup at the outset of a given task.
Regular site visits are still crucial to ensure:
- The sensors are functioning properly
- The readings are properly calibrated
Rain Gauge Calibration Check
Calibration checks on rain gauges are a common maintenance need for applications that rely on them.
After you have done things like cleaning and checking the level of your rain gauge, you can calibrate it.
You can verify the rain gauge’s accuracy by pouring a known quantity of water into it at a known flow rate to mimic a known amount of rain in an hour.
Things to Remember When Calibrating
The current standard protocols make this type of test quite easy to perform.
Here are a few things to remember when calibrating your rain gauges:
- If the data logger performs a typical measurement sequence throughout the test, simulated data may appear as actual data.
- Remembering the baseline rainfall amount will allow you to return it to that level once the test is complete.
- You may have physically unplugged the rain gauge from the logger and instead attached it to a different measurement device.
- Physically unplugging the gauge from the logger prevents the simulated data from contaminating the actual data.
- Unplugging it inappropriately can raise the possibility of an error upon reconnecting the gauge to the logger.
- Remember to reattach the gauge to the data logger if you unplug it. This may sound like a no-brainer, yet it is easy to overlook.
Other Accurate and Simple Ways to Measure Rainfall
Federal and state agencies invest considerable resources into studying the frequency and intensity of precipitation throughout the year and between seasons.
It helps them to better predict the effects of climate change. The agricultural department places equal importance on the amount of rainfall in a region as does the individual farmer.
You can use this data to calculate how much water your lawn or garden needs.
A weather station could utilize them to record precipitation data like daily totals. One such application is in a flood warning system.
What is the Most Accurate Way to Record Rain?
The weight of rainwater is 5.20 ounces per square foot of land. When it rains, it dumps 113.31 tons of water per square inch of land.
Putting a rain bucket on a scale with a known diameter (often 12 or 24 inches) is the most precise technique to measure rainfall.
To calculate how much rain fell, the scale deducts the mass of the container.
They are more precise because they do not make the common mistake of underestimating the force of heavy rain, which can influence the precision of an analog gauge, and they can also measure less common kinds of precipitation like hail and snow.
Fact: Scientists can determine how much of a certain chemical is floating around in the air or falling from the sky in a given area by attaching a special gadget to a weighing gauge.
Takeaway
How accurate are rain gauges? Modern-day rain gauges are quite accurate, provided you have calibrated them properly. Traditional rain gauges work but are often not that accurate.
Using the tipping bucket rain gauges continues to be the most accurate way to measure precipitation, but it still has some limitations that you should be aware of before putting them to use.
