Between grazing land and shifting sand

Casey Thornbrugh, Ph.D. candidate

Photograph of Casey Thornbrugh
Casey Thornbrugh, Ph.D. candidate, Department of Atmospheric Science, v. Thornbrugh is a UCAR SOARS alumnus. (Photo courtesy University of Arizona.)


Mention statistics to most middle schoolers and, unless you're talking about odds for poker hands, the response is likely to be an eye roll. When Casey Thornbrugh was in middle school, though, his hobby was climate statistics.

"I was into statistical anomalies before I ever took a statistics class," he recalls. "How many 90-degree days can a place get? New York and LA have about the same summer, temperature-wise; why can LA get 110-degree days and New York doesn't? I was asking those questions in the eighth grade."

His family didn't share his interest, but they supported him anyway. Since they didn't have Internet access, they bought him world almanacs to help him make his own climate maps.

Thornbrugh's tribal heritage (Mashpee Wampanoag) is from the northeastern woodlands and he was born in Massachusetts, but his family moved to Albuquerque, New Mexico, when he was nine. As a result, "My climate record is all in the Southwest," he explains.

As he grew older and began to think of a career, his family pointed him toward science, even though nobody knew where his unusual hobby might lead him. "People would say, 'Oh, you're going to be the first Wampanoag on the Weather Channel,' but I was more interested in climate than [regional weather] forecasting."

‘I wanted to work on something I could see with my own eyes.’

Discovering a vocation

Thornbrugh entered the University of New Mexico as a geography major. There he encountered professor David Gutzler in the Department of Earth and Planetary Sciences.

Things didn't go smoothly at first, Gutzler recalls. "In the first half of the first course he took from me," Gutzler says, "he was not one of the outstanding students; in fact, he seemed to be struggling a bit. But by the end of the class he got the highest grade. He didn't come into the class with a huge amount of background, but he sure had the motivation."

Thornbrugh stood out in another way, Gutzler recalls. "I always issue a blanket invitation to the students that if they're interested in the subject matter, they should come talk to me about doing research. He jumped on that. To be honest, I don't expect a large number of students to be leaping out of their seats to come work for free, but it's always exciting when someone does. And there's no better way to learn how to actually do science."

Gutzler put Thornbrugh to work studying the correlation between winter precipitation in New Mexico, the phase of El Niño–Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO). "I had a PC in the outer part of my office, and Casey would put on his headphones and bang away for hours at a time," he remembers, applying various compositing techniques to the data. They found that the PDO regime shift in the late 1970s changed the ENSO-related winter precipitation patterns in the Southwest. The work resulted in a published paper and a poster session at the American Meteorological Society's 2002 annual meeting.

"In essence, Dr. Gutzler gave me a graduate experience before I was a grad student," Thornbrugh says.

SOARing ahead

Thornbrugh's journey toward a career in research took a giant step forward in 2001, when he was accepted into UCAR's SOARS program (Significant Opportunities in Atmospheric Research and Science).

His first assignment was to assess the climatological airmass patterns and human health statistics associated with heat waves in Chicago and Philadelphia. "I really enjoyed the work, but I wanted to work on something I could see with my own eyes, and that would be in the Southwest," Thornbrugh says.

‘You can go online and look at the climate records, but I really need to hear it from the elders.’

His mentor at UCAR, Robert Harriss, had met scientist Margaret Hiza Redsteer (U.S. Geological Survey) at a workshop on Native American decision making on climate change; Harriss contacted her and asked if she would like an intern. "I wasn't about to turn down an opportunity like that," she says. She had Thornburgh analyze the data from the weather station on the Moenkopi Plateau. "He was very organized; he started writing right away, and by the time the summer was over he had put together a pretty good first draft of a paper. He's incredibly motivated, and his energy is infectious."

Thornbrugh enjoyed the challenge of applying climate data to a new field. "I didn't have a background in geology or geomorphology, so I had to hold on tight."

Paying it forward

As he begins his Ph.D. work, Thornbrugh hasn't forgotten what it was like to be the only kid who cared about climate. "My hope is that I can continue to do research, but that I can also continue to work with communities, with students. I know that the climate is changing, and I would like to be a part of education and planning that's going to need to be done."

Last summer, fellow University of Arizona grad students Rachel Novak (Navajo) and Andrew Knowler recruited him to join them in a climate change enrichment project for students at Monument Valley High School. They borrowed Hiza Redsteer's specialized tape measure to teach the students how to calculate the percentage of vegetation on nearby dunes.

For Thornbrugh, a highlight of the summer came when they took the young people to remote settlements to talk with older Navajos about climate. "You can go online and look at the climate records, but I really need to hear it from the elders."

About the Research

Ask Casey Thornbrugh about the fragile state of Navajo grazing lands in Arizona and he'll tell you that "the sustainability of the land is essential to the cultural and economic well-being of those who reside on it." This principle fires his work studying sand dune mobility on the Moenkopi Plateau in Arizona, a semiarid region of rolling sandhills on the southwestern side of the Navajo Nation.

In their stable state, the plateau's sandhills are covered with grasses or shrubs, providing sparse grazing for the Navajos' cattle and horses. If that cover is lost, the sandhills may become active sand dunes, barren heaps of sand that offer no feed for livestock and make transportation difficult. Winds blow these active dunes slowly across the plateau, blocking roads and threatening any buildings in their path.

Although active dunes are easily created, replanting and restabilizing them is extremely difficult.

Thornbrugh's main research tool is a widely used index of sand dune mobility, developed by Nicholas Lancaster of the Desert Research Institute. Lancaster applied the index to the Moenkopi Plateau for the years 1986 to 1997, using meteorological data from a weather station installed in 1979 for the Desert Winds Project. (Also see Geometeorological data collected by the USGS Desert Winds Project.)

Under the direction of Margaret Hiza Redsteer (U.S. Geological Survey), Thornbrugh has extended the index—and the meteorological record from the still-functioning weather station—to 2005 to observe the effects of a decade of drought. He has found that, while it correlated well with the earlier years, "the index has some challenges when you apply it from 1997 onward. The reason has to do with the time scale that it's applied to and the nature of precipitation in northern Arizona."

Map in black and white of a part of Arizona
The Moenkopi Plateau in Arizona. The USGS station at Gold Spring provides meteorological data for Thornbrugh's research. (Image courtesy U.S. Geological Survey.)

In a drought, heavy storms alter the index

The last decade has seen almost unrelenting drought in the Southwest. When rain did fall in northern Arizona, though, it sometimes came in extremely heavy individual storms. For example, two record storms in September 2002 provided 45–50% of that year's total precipitation. Applying the mobility index to the 2002 annual data, Thornbrugh obtained relatively low values, supposedly indicating that it was a year with low sand dune growth.

Photos and communication with local residents in 2002, however, demonstrated just the opposite. The parched dirt was too compacted to absorb the heavy rainfall and instead simply washed away, exposing the sand beneath.

Thornbrugh's considering ways to modify the index to account for this precipitation pattern. It might seem logical simply to apply the index to shorter periods of time to avoid dealing with the extreme events, but that doesn't work because in the real world it takes longer amounts of time for vegetation to die back and active dunes to develop.

Future work: The potential for seasonal forecasts

One of Thornbrugh's goals is to use the index in connection with climate forecasts.

Others have combined index data with global model output to forecast dune growth in the coming decades in the U.S. Great Plains, but when it comes to the Southwest, the models disagree greatly about how precipitation will change. He would prefer to use the index with shorter-term forecasts.

"What people would really find useful, especially people who have livestock, is using the index with shorter-term climate data, for example, getting an outlook in the winter of what the coming spring and summer are anticipated to be."

Thornbrugh, who is Native American, hopes that his project will benefit the people of the Moenkopi Plateau and throughout the Navajo Nation. With their deeply ingrained tradition of "belonging to"—not owning—the land, the Navajos will be looking for additional resources and information that they can apply to protect their fragile environment. "Climate change has happened to these people before, and they've dealt with it. In the communities I work with, people are really positive. They will get really upset with you if you just present the problem. The best presentation is, 'This is what might happen, and here are some solutions that have worked in other places.' "


The dune mobility index

"It's very simple, really," is how Nicholas Lancaster explains his dune mobility index, developed in 1988. "Basically, the movement of dunes is directly proportional to the presence of strong winds and inversely proportional to the presence of vegetation." In other words, if there's a lot of wind and not much vegetation, dunes blow away; if there's plenty of groundcover and not much wind, they don't.

The formula is: M  =   W

where M is dune mobility, W is the percentage of time that the wind blows about the threshold velocity for sand transport, P is annual rainfall, and PET is potential evapotranspiration (a measure of the atmosphere's ability to remove water from plants).

The wind threshold velocity varies according to the fineness or coarseness of the sand being studied. Solving the equation with data from a stable, plant- or grass-covered area, such as the Nebraska Sandhills, will give a low value—say, around 50. Values of 200 or higher indicate a great danger that the region will degrade into barren, blowing sand. Using northern Arizona data from drought years, Thornbrugh has seen values as high as 400.

Although the index accounts for the major factors affecting sand dune mobility, there are other climatological and land-use factors that would need to be included for a truly complete forecast, such as whether precipitation falls as rain or snow and what kinds of livestock graze on the sandhills.

May 2007

One-minute mentor

What advice would you offer to someone interested in a career like your own?

Find support while you're in high school

If you have an interest in weather and climate and can't find anyone else at school who does, seek outside support, says Casey Thornbrugh. "If students don't have an opportunity to put their interest to use, it's very easy to get discouraged. You think, 'Nobody cares about what I do.' " If you're in an urban area, he suggests, start looking for volunteer work at your local weather service office. If you're in a rural area or on the reservation, look for summer programs that you might apply for, even if they don't pay. They can keep your interest alive for the rest of the year, and you might find a mentor and further opportunities.

Casey Thornbrugh, Ph.D. candidate

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