Collecting Precipitation Data - January 27, 2010
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County

Many people have a backyard rain gauge where they measure and record precipitation data. I have a rain gauge at my home and have kept records since 2002. Precipitation measurements give me a rough idea of how long I can go between irrigating my garden and fruit trees and makes for great conversation. I think many readers would enjoy measuring and recording precipitation data at their homes. I will also tell you about an ongoing program where you can share your precipitation data with researchers at the University of Arizona.

Precipitation amounts are highly variable across Arizona due to topography and seasonal weather patterns. This is especially true during the Arizona monsoon, when thunderstorms produce heavy rainfall that is very localized. The National Weather Service, County Flood Control Departments, and other government entities have many weather stations across the state, but there are still relatively large distances between these official weather stations. Scientists are trying to understand if there is an underlying cause to this spatial variability and if they can determine factors driving variability.

Various simple rain gauges are available through catalogs and the Internet. The most common types are the wedge type, cylinder or rectangular, and funnel catch with overflow. Most are made of plastic or polycarbonate and cost between $10 and $30. The wedge type has the advantage of accuracy when recording small amounts, but is limited to six inches of precipitation between readings. Cylinder or rectangular types are less accurate, but inexpensive. The funnel catch with overflow has a large collection area, but loses accuracy when measuring rainfall amounts greater than one inch.

Digital rain gauges are also available and are becoming more affordable. Some models use tipping bucket technology and another uses a calibrated tube that forms uniform drops which are counted by a sensor. The tipping bucket type trips a switch when the bucket is dumped and the remote base stations receive the signal via wireless technology so you can read the precipitation data from the comfort of your home. Digital rain gauges range in price from $40 to $60.

The most critical consideration in collecting rainfall data is the location of your gauge. Site your gauge in an open area away from obstructions such as trees or overhangs, and in an area protected from high winds. Mount your gauge on a post at a height of 3 to 5 feet with the gauge extending several inches beyond the post. Make sure that the top of the gauge is level. Avoid areas where rainwater can indirectly splash from sheds, equipment, carports, etc. If you have a large area, such as a ranch or farm, consider installing multiple rain gauges.

Are you interested in becoming an official precipitation observer? The University of Arizona Cooperative Extension and the SAHRA Water Center (also at U of A) are recruiting citizen scientists to help monitor rainfall across Arizona. The Rainlog project is an effort to better monitor and characterize rainfall patterns. You can collect and share precipitation information to make better decisions about how we use water in our own backyards all the way up to how we manage water resources across Arizona. Rainlog is centered at a website: Here, observations are entered on your home computer to create maps that show other rainloggers’ precipitation data across the southwest.

Participating in is easy and anyone with a backyard rain gauge can join. Web site registration includes a Google map utility to pinpoint the latitude and longitude of gauge locations, plus guidance on selecting and installing rain gauges and information on how to collect high quality observations. High quality, wedge type rain gauges are also available for $12 including shipping. You might consider ordering two to have a backup. Uploading data after rain events is a simple, straight-forward process using web forms. There are several rainloggers in the Verde Valley, but we can always use more data. I hope some readers will become rainloggers – it’s fun and contributes to our greater understanding of climate variability.

The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site:

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: January 21, 2010
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