Choosing The Right Rain Gauge

Question: How do I choose the right rain gauge so I know when my garden and landscape need water?

Climate change is bringing us periods of drought and periods of more excessive rainfalls as well as higher temperatures. Heat stress causes greater water demands in your garden, but you should irrigate only when rainfall is inadequate.

A rain gauge can be a simple, inexpensive tool for determining if your specific property has received too little or too much water. It can provide more accurate data for your landscape than official weather services reporting on rainfall measurements taken miles from your home.

The many types of rain gauges fall into two basic categories: manual gauges that are read and emptied outdoors, and automated gauges that self-empty, record their readings, and send them to a digital display indoors.

To choose the best instrument for accurately meeting your rainfall measurement needs, consider both the types of rain gauges available and where the gauge will be placed in the landscape. The accuracy, cost, ease of use, maintenance required, and how the rain gauge will work with your lifestyle should also factor into your decision.

Standard manual rain gauges are the cheapest and most straightforward option. These rain gauges are typically clear acrylic or glass cylinders, and usually marked in inches, centimeters, or millimeters. Some designs are less accurate than others. Plastic rain gauges that have a 4-inch-diameter opening at the top are fairly accurate and are considered adequate for home use. Those who prefer more precision can follow the lead of The National Oceanic and Atmospheric Association (NOAA) weather observer network and use a standard manual gauge with an 8-inch opening, which are considered the most accurate. Many of the plastic gauges that are “give aways” to the public are not 4-inch-diameter gauges. Gauges with smaller openings (some are as small as a test tube) give only a general, less accurate estimate of rainfall amounts.

Funnel-bucket gauge

Funnel-bucket gauges are another type of manual gauge with a more sophisticated design. The funnel is typically a tapered shape, connected to a graduated cylinder that allows for the gradual expansion as the funnel fills with more rain. This cylinder sits in a bucket to catch the overflow. This type of rain gauge is recommended for amateur home weather observers by the National Weather Service (https://weather.gov). Although considered more accurate than standard gauges, this type requires removal of the top funnel and self-emptying of the inner tube after each rainfall to take measurements.

Automated rain gauges include tipping bucket gauges, weighing precipitation gauges and wireless digital and home weather station rain gauges. They are complicated in design and because of the wide variety of models, each one should be evaluated for home use based on the specific features it offers. For more information on automated rain gauges, see the August 2023 “Timely Topic” posted on piedmontmastergardeners.com. 

La Crosse Technology

Regardless of the rain gauge selected, where you place a rain gauge can affect its accuracy. Proper siting and placement often depend upon connectivity to wireless networks (if needed), maintenance accessibility, consideration of local wind patterns, and avoidance of physical obstructions. Here are some considerations:

  • Place the gauge at least 2-5 feet off the ground on the side of a pole, a fence, or deck post in an open space. The top of the cylinder should be several inches above the top of the pole or post to avoid splash-back.
  • The top of the rain gauge should be level.
  • Keep your rain gauge away from obstructions that can keep water from entering, such as a tree branch. Mounting too close to your roof, trees, or buildings can cause inaccurate readings during heavy rain events. A general rule of thumb is to place the rain gauge twice the distance away from the height of the nearest obstruction (e.g., placing a gauge 20 feet away from 10-foot-tall trees).
  • Don’t locate gauges on elevated sites, such as tops of knolls, to avoid wind turbulence problems that can cause the gauge to underreport actual rainfall. The windier the location, the greater the precipitation measurement error will be.
  • Keep the gauge away from sources of artificial precipitation such as sprinklers.

In general, the ideal location would be at a corner of your garden, deck or yard, free from excessive wind and any obstacles that might interfere with the collection of rain.  An area that you walk past daily will help you remember to read and empty the gauge.

The point is to collect reasonably accurate data specifically for your property and the 4-inch-diameter manual rain gauge is adequate for that purpose. With this manual rain gauge properly sited and placed, the user can read the gauge at eye level, looking at the lowest point at the base of the curved rainwater surface (called the meniscus) and take the measurement at that point. It’s an easy way to obtain rainfall data needed to help you avoid over- or underwatering your plants.

Whichever rain gauge you choose, develop a routine and record your rainfall measurement at the same time each day—just like brushing your teeth in the morning. Or keep it simple by recording and emptying a manual rain gauge on a weekly basis. Pick your day of the week to do this.

No matter where you landscape or garden, water is a resource that should never be taken for granted. Increasing the soil’s water-holding capacity by adding organic matter is another good way to make sure plants have water when they need it. Work on building your soil, set up a rain gauge, and start monitoring!

Image sources: Weather Station Advisor

References

“Accuracy of rain gauge measurements”, Carrol, Dr. Juliet,  Cornell University, Network for Environment and Weather Applications, 18 Jun 2015

“Rain Gauges: What They Are, How They Work, And the Different Types of Rain Gauges”, Own Your Weather, 13 Jan 2023

 “Why Use a Rain Gauge?” , Quartararo, Marianna, Resource Conservationist, Pike County Conservation District, 18 Oct 2018