Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Loss of Summer Rains Stoked Long Droughts in Southwest

12.03.2013
Long-term droughts in southwestern North America often mean failure of both winter and summer rains, according to new tree-ring research.

The finding contradicts a commonly held belief regarding the region – that a dry winter rainy season is generally followed by a wet summer season, and vice versa. In fact, when severe, decades-long droughts have struck the area in centuries past, both winter and summer rains generally were sparse year after year, the new study shows.

"One of the big questions in drought studies is what prompts droughts to go on and on," said lead author Daniel Griffin, a doctoral candidate in the School of Geography and Development of the University of Arizona in Tucson. "This gives us some indication that the monsoon and its failure is involved in drought persistence in the Southwest."

A monsoon is a season of heavy rains caused by air rising over warm land, which draws in cooler, more humid air from the ocean. In most of Arizona, western New Mexico, and parts of northern Mexico--where the monsoon lasts from late spring to early fall--moisture-laden winds blow in from the Gulf of California and the eastern tropical Pacific Ocean.

The new study’s results surprised Griffin because rain gauge records for the Southwest from 1950-2000 show that dry seasons alternated with wet ones. However, the team’s new 470-year-long record, going from 2008 all the way back to 1539, shows that the wet/dry pattern of the latter part of the 20th century is not the norm – either prior to the 20th century or now, he said.

The research report by Griffin and his colleagues was published today, March 11, in Geophysical Research Letters, a journal of the American Geophysical Union.

"This is the first time researchers have used tree rings to take a closer look at the monsoon in a large and important area of the American Southwest," Griffin said. "Monsoon droughts of the past were more severe and persistent than any of the last 100 years," he added. "These major monsoon droughts coincided with decadal winter droughts."

Those droughts had major environmental and social effects, Griffin said, pointing out that the late-16th-century megadrought caused landscape-scale vegetation changes, a 17th-century drought has been implicated in the Pueblo Revolt of 1680 and the 1882-1905 drought killed more than 50 percent of Arizona’s cattle.

"The thing that’s interesting about these droughts is that we’ve reconstructed the winter precipitation, but we’ve never known what the summers were like," said co-author Connie A. Woodhouse, also of the University of Arizona, Tuscon.

Because winter precipitation has the strongest influence on annual tree growth, previous large-scale, long-term tree-ring reconstructions of the region’s precipitation history had focused only on the winter rainy season. "Now we see – wow – the summers were dry, too," Woodhouse said. "That has a big impact."

"In the Southwest, the winter precipitation is really important for water supply. This is the water that replenishes reservoirs and soil moisture," she said. "But the monsoon mediates the demand for water in the summer."

Until recently, most tree-ring researchers, known as dendrochronologists, have looked at the total width of trees’ annual rings to reconstruct past climate. Few teased out the seasonal climate signal recorded in the narrow part of the growth ring laid down in late summer known as latewood.

To figure out the region’s past history of monsoon precipitation, the scientists needed to measure latewood from tree-ring samples stored in the archives of the University of Arizona Laboratory of Tree-Ring Research and go into the field to take additional samples of tree rings.

The team looked at annual growth rings from two different species, Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) throughout the weather forecast region called North American Monsoon Region 2, or NAM2.

In all, the researchers used samples from 50 to 100 trees at each of 53 different sites throughout southwestern North America. The team’s climate analyses focused on NAM2, which covers most of Arizona, western New Mexico and northern parts of the Mexican states of Sonora and Chihuahua.

Griffin said, "It was a massive undertaking -- we employed about 15 undergraduates over a four-year period to measure almost 1 million tree rings."

One possible next step, Woodhouse said, is to expand the current project to other areas of the Southwest and into Mexico, where the monsoon has a bigger influence on annual precipitation.

Another would be using tree-ring reconstructions of the Southwest’s fire histories to see how wildfires are related to summer precipitation.

"Before I moved to the Southwest, I didn’t realize how critically important the summer rains are to the ecosystems here," Griffin said. "The summer monsoon rains have allowed humans to survive in the Southwest for at least 4,000 years."

The National Science Foundation, the National Oceanic and Atmospheric Administration and the U.S. Environmental Protection Agency supported the research.

Title:

“North American monsoon precipitation reconstructed from tree-ring latewood”
Authors:
Daniel Griffin and Connie A. Woodhouse Laboratory of Tree-Ring Research and School of Geography and Development, University of Arizona, Tucson, USA;David M. Meko Laboratory of Tree-Ring Research, University of Arizona, Tucson, USA;David W. Stahle Department of Geosciences, University of Arkansas, Fayetteville, USA;Holly L. Faulstich Laboratory of Tree-Ring Research and School of Geography and Development, University of Arizona, Tucson, USA;Carlos Carrillo Department of Atmospheric Sciences, University of Arizona, Tucson, USA;Ramzi Touchan Laboratory of Tree-Ring Research, University of Arizona, Tucson, USA;Christopher L. Castro Department of Atmospheric Sciences, University of Arizona, Tucson, USA;Steven W. Leavitt Laboratory of Tree-Ring Research, University of Arizona, Tucson, USA.

Contact information for the authors:

Contact information for the authors:
Daniel Griffin
School of Geography and Development
Laboratory of Tree-Ring Research
520-621-0858
dgriffin@email.arizona.edu
http://u.arizona.edu/~dgriffin/
Connie Woodhouse
School of Geography and Development
Laboratory of Tree-Ring Research
520-626-0235
conniew1@email.arizona.edu
http://cwoodhouse.faculty.arizona.edu

Peter Weiss | American Geophysical Union
Further information:
http://www.agu.org

More articles from Earth Sciences:

nachricht Predicting unpredictability: Information theory offers new way to read ice cores
07.12.2016 | Santa Fe Institute

nachricht Sea ice hit record lows in November
07.12.2016 | University of Colorado at Boulder

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Electron highway inside crystal

Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.

Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers identify potentially druggable mutant p53 proteins that promote cancer growth

09.12.2016 | Life Sciences

Scientists produce a new roadmap for guiding development & conservation in the Amazon

09.12.2016 | Ecology, The Environment and Conservation

Satellites, airport visibility readings shed light on troops' exposure to air pollution

09.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>