Citizen Scientists Collect Rainfall Data Across Arizona

Published: Thursday, December 22, 2016 - 5:00am
Updated: Monday, December 26, 2016 - 10:25am

(Photo by Sara Hammond - KUAZ)
Rainfall is measured in more that 500 rain gauges across Arizona for the UA Rainlog project.

Babies are born natural scientists, exploring the world and discovering how things work. But few grow up to be scientists. In our five-part citizen science series, we look at how everyday citizens are contributing to science with the help of trained professionals.


Hundreds of people in Arizona voluntarily keep an eye on rainfall totals in their yards and report them to a database used by utilities, government agencies, gardeners, researchers, even weather geeks. Each rainlogger is a citizen scientist.

The University of Arizona-based rainlog.org project collects rainfall data from individuals across Arizona. The program started more than 15 years ago as a way to gather rainfall information around the upper San Pedro River in Cochise County.

Water resource expert Gary Woodard is one of the founders.

“Some of the researchers came to me and said we need a way for volunteers to report rainfall in the Sierra Vista area," Woodard said. "They thought maybe eight or 10 folks that could report it weekly."

Within a couple of years, more than 500 people in Pima County had backyard gauges. They were joined by 350 in Maricopa County, and clusters in other parts of the state and country. Woodard said the numbers are now down a bit — the program has limited funding and is promoted largely by word of mouth.

“Some people do not report every day when it doesn’t rain. But some people report every single day," Woodard said. "Other people mostly just when it does rain. Reports just pour in the morning after an active monsoon day.”

The database can be manipulated to show rainfall by an individual weather event, by year or cumulatively.

Martha Retallick has been recording rainfall data at her central Tucson home for more than five years.

“I like statistics, I like data," Retallick said.

In addition to the hundreds of people who record data on the website, thousands of others benefit by registering as rain mappers. Each gets an email when rainfall in their surrounding area has been recorded

Margrit McIntosh is one of those weather watchers.

McIntosh said she has been recording rainfall totals since she moved to Tucson in 1994. If she’s away, she relies on rainlog.org to fill in the blanks.

“If I’m not sure what I got in my rain gauge, how accurate that is or I was out of town when there was a rain event, I check rainlog.org to see what the people in my neighborhood who are reporting rainfall have reported," she said.

McIntosh is an ecologist who is studying an endangered cactus in the Waterman Mountains near Tucson. She says her team’s research would benefit if there were rain loggers near the study area.

“I sort of wish there was somebody who had a house out at the end of Avra Valley Road who had a rain gauge and was reporting to rainlog.org cause then we would have closer data,” McIntosh said.

Woodard said he is pleased that rainlog.org is used for a variety of purposes.

“What really caught me by surprise was the variety of groups and individuals that started using the data for purposes we never imagined," Woodard said.

Woodard remembered a call he received from an attorney who had to prove that it had rained at a particular intersection in Tucson on a specific day. The official rain gauge at Tucson International Airport had recorded no rain that day, but rainlog.org’s data told a different story.

“The [Arizona] Department of Environmental Quality has a number of superfund sites and other locations where there has been pollution in the past," Woodard said, "and if they get a certain amount of rain they have to go out and take water quality samples, test the quality of the runoff from these sites. And they rely on rainlog to figure out if it actually rained near some of these sites.”

Rainfall measured in more the 500 gauges across Arizona is logged on this site.

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