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 Impacts of mass coral die-off on Indian Ocean reefs revealed
21.02.2017 | University of Exeter

nachricht How much biomass grows in the savannah?
16.02.2017 | Friedrich-Schiller-Universität Jena

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Microhotplates for a smart gas sensor

22.02.2017 | Power and Electrical Engineering

Scientists unlock ability to generate new sensory hair cells

22.02.2017 | Life Sciences

Prediction: More gas-giants will be found orbiting Sun-like stars

22.02.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>