Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Southwest sliding into a drier climate


Weather patterns that bring moisture are becoming less frequent

The weather patterns that typically bring moisture to the southwestern United States are becoming more rare, an indication that the region is sliding into the drier climate state predicted by global models, according to a new study.

Weather systems that typically bring moisture to the southwestern United States are forming less often, resulting in a drier climate across the region. This map depicts the portion of overall changes in precipitation across the United States that can be attributed to these changes in weather system frequency. The gray dots represent areas where the results are statistically significant. Map courtesy of Andreas Prein, NCAR.

Map courtesy of Andreas Prein, NCAR. This image is freely available for media & nonprofit use.

"A normal year in the Southwest is now drier than it once was," said Andreas Prein, a postdoctoral researcher at the National Center for Atmospheric Research (NCAR) who led the study. "If you have a drought nowadays, it will be more severe because our base state is drier."

Climate models generally agree that human-caused climate change will push the southwestern United States to become drier. And in recent years, the region has been stricken by drought. But linking model predictions to changes on the ground is challenging.

In the new study--published online today in the journal Geophysical Research Letters, a publication of the American Geophysical Union--NCAR researchers grapple with the root cause of current drying in the Southwest to better understand how it might be connected to a warming climate.

--Subtle shift yields dramatic impact--

For the study, the researchers analyzed 35 years of data to identify common weather patterns--arrangements of high and low pressure systems that determine where it's likely to be sunny and clear or cloudy and wet, among other things. They identified a dozen patterns that are typical for the weather activity in the contiguous United States and then looked to see whether those patterns were becoming more or less frequent.

"The weather types that are becoming more rare are the ones that bring a lot of rain to the southwestern United States," Prein said. "Because only a few weather patterns bring precipitation to the Southwest, those changes have a dramatic impact."

The Southwest is especially vulnerable to any additional drying. The region, already the most arid in the country, is home to a quickly growing population that is putting tremendous stress on its limited water resources.

"Prolonged drought has many adverse effects," said Anjuli Bamzai, program director in the National Science Foundation's Division of Atmospheric and Geospace Sciences, which funded the research, "so understanding regional precipitation trends is vital for the well-being of society. These researchers demonstrate that subtle shifts in large-scale weather patterns over the past three decades or so have been the dominant factor in precipitation trends in the southwestern United States."

The study also found an opposite, though smaller, effect in the Northeast, where some of the weather patterns that typically bring moisture to the region are increasing.

"Understanding how changing weather pattern frequencies may impact total precipitation across the U.S. is particularly relevant to water resource managers as they contend with issues such as droughts and floods, and plan future infrastructure to store and disperse water," said NCAR scientist Mari Tye, a co-author of the study.

--The climate connection--

The three patterns that tend to bring the most wet weather to the Southwest all involve low pressure centered in the North Pacific just off the coast of Washington, typically during the winter. Between 1979 and 2014, such low-pressure systems formed less and less often. The associated persistent high pressure in that area over recent years is a main driver of the devastating California drought.

This shift toward higher pressure in the North Pacific is consistent with climate model runs, which predict that a belt of higher average pressure that now sits closer to the equator will move north. This high-pressure belt is created as air that rises over the equator moves poleward and then descends back toward the surface. The sinking air causes generally drier conditions over the region and inhibits the development of rain-producing systems.

Many of the world's deserts, including the Sahara, are found in such regions of sinking air, which typically lie around 30 degrees latitude on either side of the equator. Climate models project that these zones will move further poleward. The result is a generally drier Southwest.

While climate change is a plausible explanation for the change in frequency, the authors caution that the study does not prove a connection. To examine this potential connection further, they are studying climate model data for evidence of similar changes in future weather pattern frequencies.

"As temperatures increase, the ground becomes drier and the transition into drought happens more rapidly," said NCAR scientist Greg Holland, a co-author of the study. "In the Southwest the decreased frequency of rainfall events has further extended the period and intensity of these droughts."


The study was funded in part by the National Science Foundation, NCAR's sponsor, and the Research Partnership to Secure Energy for America.

Other co-authors of the study include NCAR scientists Roy Rasmussen and Martyn Clark.

The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Media Contact

Laura Snider


Laura Snider | EurekAlert!

More articles from Earth Sciences:

nachricht Ice shelf vibrations cause unusual waves in Antarctic atmosphere
25.10.2016 | American Geophysical Union

nachricht Enormous dome in central Andes driven by huge magma body beneath it
25.10.2016 | University of California - Santa Cruz

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Etching Microstructures with Lasers

Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.

This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...

Im Focus: Light-driven atomic rotations excite magnetic waves

Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion

Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

All Focus news of the innovation-report >>>



Event News

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

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Ice shelf vibrations cause unusual waves in Antarctic atmosphere

25.10.2016 | Earth Sciences

Fluorescent holography: Upending the world of biological imaging

25.10.2016 | Power and Electrical Engineering

Etching Microstructures with Lasers

25.10.2016 | Process Engineering

More VideoLinks >>>