U.S. during past 40 years
Largest changes centered over Rio Grande region of Southwestern U.S.


Date:
April 6, 2022
Source:
Desert Research Institute
Summary:
In arid Western states, the climate is growing warmer and drier,
leading to increased demand for water resources from humans and
ecosystems. Now, the atmosphere across much of the U.S. is also
demanding a greater share of water than it used to, according to
a new study.



FULL STORY ==========================================================================
In arid Western states, the climate is growing warmer and drier, leading
to increased demand for water resources from humans and ecosystems. Now,
the atmosphere across much of the U.S. is also demanding a greater share
of water than it used to, according to a new study by a team from DRI, University of California, Merced, and Scripps Institution of Oceanography
at UC San Diego.


==========================================================================
The study was published in the Journal of Hydrometeorology and assessed
trends in evaporative demand across the U.S. during a 40-year period from 1980-2020 using five datasets. Evaporative demand, sometimes described
as "atmospheric thirst," is a measure of the potential loss of water
from the earth's surface to the atmosphere based on variables including temperature, humidity, wind speed, and solar radiation.

The team's findings showed substantial increases in atmospheric thirst
across much of the Western U.S. during the past 40 years, with the largest
and most robust increases in an area centered around the Rio Grande and
Lower Colorado rivers. These regions have experienced changes on the
order of two-to-three standard deviations from what was seen during the baseline period of 1980-2000.

"This means that atmospheric thirst conditions in parts of the country are
now verging outside of the range that was experienced 20 to 40 years ago, especially in some regions of the Southwest," said lead author Christine Albano, Ph.D., of DRI. "This is really important to understand, because
we know that atmospheric thirst is a persistent force in pushing Western landscapes and water supplies toward drought." To learn more about the
role that different climate variables play in determining atmospheric
thirst, Albano and her colleagues analyzed the relative influences of temperature, wind speed, solar radiation, and humidity. They found that,
on average, increases in temperature were responsible for 57 percent of
the changes observed in all regions, with humidity (26 percent), wind
speed (10 percent), and solar radiation (8 percent) playing lesser roles.

"This study shows the dominant role that warming has played on the
increasing evaporative demand and foreshadows the increased water
stressors the West faces with continued warming," said study co-author
John Abatzoglou, Ph.D., of the University of California, Merced.



==========================================================================
For farmers and other water users, increases in atmospheric thirst mean
that in the future, more water will be required to meet existing water
needs. Some of these changes observed in this study are centered over
areas where warming temperatures and lower-than-average precipitation
are already creating stress on water supplies.

For example, in the Rio Grande region, the study authors calculated
that atmospheric thirst increased by 8 to 15 percent between 1980 and
2020. Holding all else equal and assuming no other changes in management,
this means that 8 to 15 percent more water is now required to maintain
the same thoroughly- watered crop.

"Our analysis suggests that crops now require more water than they did
in the past and can be expected to require more water in the future,"
said study co- author Justin Huntington, Ph.D., of DRI.

Other impacts of increased atmospheric thirst include drought, increased
forest fire area, and reduced streamflows.

"Our results indicate that, decade by decade, for every drop of
precipitation that falls, less and less water is likely to drain into
streams, wetlands, aquifers, or other water bodies," said study co-author Michael Dettinger, Ph.D., of Scripps Institution of Oceanography and
DRI. "Resource managers, policy makers, and the public need to be aware
of these changes and plan for these impacts now and into the future."
Members of the team are now developing seasonal to sub-seasonal forecasts
of evaporative demand.

"We anticipate these types of forecasts will be important for drought
and fire forecasting applications," said study co-author Dan McEvoy,
Ph.D., of DRI.


========================================================================== Story Source: Materials provided by Desert_Research_Institute. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Christine M. Albano, John T. Abatzoglou, Daniel J. McEvoy, Justin L.

Huntington, Charles G. Morton, Michael D. Dettinger, Thomas
J. Ott. A Multidataset Assessment of Climatic Drivers and
Uncertainties of Recent Trends in Evaporative Demand across the
Continental United States.

Journal of Hydrometeorology, 2022; 23 (4): 505 DOI:
10.1175/JHM-D-21- 0163.1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220406132356.htm

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