Southwest Environment

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Department of Soil, Water and Environmental Science
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Network of ‘citizen scientists’ to track climate change

Jake WeltzinPhoto by Tim McDonnell
Jake Weltzin, NPN executive director, calls phenology a “simple, integrative indicator”of climate change. Weltzin hopes to use the NPN to amass an army of “citizen scientists.

By Tim McDonnell, May 2009

If you’ve ever made mental note of the first flower in spring or the first orange leaf in fall, you’re already a potential phenologist, even if you’ve never heard the term before.

Phenology, or the study of the timing of seasons, is at the center of a new project known as the National Phenology Network, led by the U.S. Geological Survey and housed at the University of Arizona’s Office of Arid Land Studies.

The project aims to amass a giant database of phenological observations, such as blooming flowers and arriving birds to track changes in seasonal timing.

If you think this sounds like something anyone could help do, you’re right.

Much of the NPN is that data is collected from what Executive Director Jake Weltzin calls “citizen science monitors,” everyday members of the public who use worksheets provided online by the NPN to record data about the plants and animals in their own backyards. Botanists and scientists can participate at more involved levels.

“Scientists are few and far between,” Weltzin said, adding that the simplicity of some phenological observation makes is possible and practical to enlist lay people to contribute to the scientific cause.

The NPN has been operating publicly since March 2009 and already boasted 2,500 users by May.

Why phenology? The answer, Weltzin said, is that it can be “a simple, integrative indicator” of climate change.

“The timing of when saguaro blossoms, for example, is a function of a lot of different driving variables: rainfall, soil moisture, temperature, day length,” he said. “But by getting a good handle on flower timing and linking it to those different variables you can get a good handle on what’s the primary driving variable.”

That primary driving factor, said NPN Network Liaison Theresa Crimmins, is often temperature.  The Intergovernmental Panel on Climate Change reported in 2007 that average global temperatures could rise  several more degrees by mid-century, on top of the 1.4 degree Fahrenheit increase observed from 1900 through 2005.  

The temperature rise has an impact on phenology, such as by changing the patterns of species migration.

The monarch butterfly, Danaus plexippus, is cued to migrate when the sun reaches a certain angle in its yearly rotation, Crimmins said. The butterfly feeds and pollinates a number of plant species that bloom when the weather is warm enough.

Because the sun’s pattern is the same every year, the butterflies always migrate at the same time. But as temperatures rise earlier in the season, plants bloom earlier as well. The result, Crimmins said, is that the monarchs might miss their chance to eat.

But the NPN doesn’t exist for the sake of butterflies, however unfortunate their situation, Crimmins said. Ultimately, the idea is to use phenological data to help make decisions about land management.

“We need to better understand how ecosystems are responding to climate change,” Crimmins said. “This network can also help us, as humans, adapt to this and inform management decisions about land use.”

Having a widespread network of citizens rather than a concentrated group of scientists is essential to the project’s success, Weltzin said, because people are often able to notice things in their backyards that might not get picked up by the kinds of imaging techniques generally employed to assess phenological factors, such as overall greenness.

The NPN’s method is simple: interested contributors register at, selecting a location and species of plant to observe. The network is available all across the U.S., but is not yet programmed to accept animal observations. Contributors then print out a worksheet specially designed for that species with a series of simple observational questions. This data is entered online, with observations continuing for as long as the contributor is interested.

The process is exciting, Crimmins said, but by no means new: people have been informally collecting phenological data for centuries. Although it is difficult to scientifically standardize great-grandma’s diary entries about the arrival of bluebirds, such data could prove invaluable, she said.

“If we can bring together data sets that folks have been collecting for the past 10, 20, 30, 100 years, we suddenly can look backwards, and expand our record immensely, and you can’t put a value on that,” she said.

Britain has hosted a similar program, the Butterfly Monitoring Scheme, since 1976. The program utilizes a ‘citizen scientist’ watch network similar to NPN’s, although confined solely to butterflies.

The BMS gathers reports from 134 sites across Britain, according to its website. Canada, the Netherlands and other European countries also have been monitoring changes in phenology for many years, via scientific studies and citizen efforts.

Ironically, one of the biggest challenges scientists will face in interpreting this information is deciding how to actually attach a date to the “arrival” of a season. Part of the difficulty, Weltzin said, is that some methods for date assigning work well in some geographic locations but not in others.

“Different natural systems do things differently,” Weltzin said. “We’re trying to establish a single point along a spectrum of space and time that defines that system, and it’s almost impossible to do.”

To illustrate, Weltzin pointed to a mesquite tree outside his office window.

“We can see that it has green leaves on it, but it had green leaves on it all winter long,” he said. “It never gets cold enough to kill the old leaves, so gradually new ones come out and push the old ones off. Probably all those leaves we see up there now are new, I guess, so when did the season start for that? When the first new green leaf came out, you could argue. Or was it when there were new leaves on three parts? That’s what we’re trying to standardize.”

For information about how to become an NPN contributor, visit and click the ‘participate’ heading at the top of the screen.

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