Global Warming Bringing Perpetual Drought

Global Warming Bringing Perpetual Drought



   
April 2007 - Human-caused climate 
change is likely to lead to long periods of extreme drought 
throughout the American Southwest starting early this century, 
finds a new study released today by the Lamont-Doherty Earth 
Observatory, a member of The Earth Institute at Columbia 
University. 
The researchers compared the coming drought to the Dustbowl of 
the 1930s that sent millions of environmental refugees fleeing 
to California from across the Great Plains. 
In contrast to past droughts, future drying is not linked to 
any particular pattern of change in sea surface temperature 
but seems to be the result of "an overall surface warming 
driven by rising greenhouse gases," researchers said. 
"The arid lands of southwestern North America will imminently 
become even more arid as a result of human-induced climate 
change just at the time that population growth is increasing 
demand for water, most of which is still used by agriculture," 
said Richard Seager, senior research scientist at the 
Lamont-Doherty Earth Observatory and one of the lead authors 
of the study. 
Sprinklers moisten a field in arid Arizona, where agriculture 
depends on irrigation. 
Projections of climate change caused by human activities 
conducted by 19 different climate modeling groups around the 
world, using different climate models, show widespread 
agreement that southwestern North America, and the subtropics 
in general, are heading toward a climate even more arid than 
it is today. 
Appearing today in the journal "Science," the research shows 
that there is a broad consenvironment newsus amongst climate models that 
this region will dry in the 21st Century and that the 
transition to a more arid climate may already be underway. 
If these models are correct, the levels of aridity of the 
recent multiyear drought, or the Dustbowl and 1950s droughts, 
will, "within the coming years to decades, become the new 
climatology of the American Southwest," the researchers said. 
"Our study emphasizes the fact that global warming not only 
causes water shortage through early snow melt, which leads to 
significant water shortage in the summer over the Southwest, 
but it also aggregates the problem by reducing precipitation," 
said Mingfang Ting, one of the study's co-authors. 
Desert near El Paso, Texas 
As the planet warms, the study documented how the Hadley Cell, 
which links together rising air near the Equator and 
descending air in the subtropics, expands toward the poles. 
Descending air suppresses precipitation by drying the lower 
atmosphere, so this process expands the subtropical dry zones.
 At the same time, and related to this, the rain-bearing 
mid-latitude storm tracks also shift poleward. 
Both changes in atmospheric circulation, which are not fully 
understood, cause the poleward flanks of the subtropics to 
dry. 
Other land regions expected to be affected by subtropical 
drying include southern Europe, North Africa and the Middle 
East as well as parts of South America. 
"The West, and in particular, the United States and Mexico, 
need to plan for this right now, coming up with new, 
well-informed and fair deals for allocation of declining water 
resources," warned author Seager. 
Las Vegas Valley Water District spokesman Scott Huntley says 
the study reinforces what Colorado River water users like the 
city of Las Vegas are experiencing right now. "Ground zero is 
right here in Las Vegas," he said. 
"This really is the wake-up call to all of the desert 
Southwest to cooperate to develop solutions," said Huntley. 
"We have seen the effects in Lake Powell and in Lake Mead - 
we've seen that the usage of water along the Colorado has been 
greater than the flows for seven or eight years now. This has 
to be the incentive for states and water users to come 
together." 
This 2003 photo of the white border around Lake Mead, a water 
storage reservoir behind the Hoover Dam, shows how full the 
reservoir once was. The lake level has fallen even farther 
since then. 
Agriculture is still by far the dominant water user - 85 
percent of water useage in the desert Southwest is for 
agriculture, Huntley explained. 
While water used to turn the arid Southwest into fertile 
fields brings vegetables, grains and fruits to market, up to 
90 percent of the water used for irrigation in the Southwest 
is lost. It evaporates from the soil or transpires from crops 
and is not returned to its source for reuse. 
Huntley says many solutions are possible if there is 
cooperation between states and between agriculture and 
municipalities. 
Conservation and efficiency are important, he said, 
desalination is a possibility, and municipalities might 
purchase water rights from farmers to keep their fields 
fallow. 
In addition, he said, states might go outside of the Colorado 
River basin to utilize groundwater. 
Roger Manning, executive director of the Arizona Municipal 
Water Users Association, AMWUA, says there is already a 
drought in Arizona, but the association's member communities - 
Chandler, Gilbert, Glendale, Goodyear, Peoria, Phoenix, Mesa, 
Tempe, and Scottsdale - have been taking steps over the past 
few years to environment newsure that the worst effects of the drought will 
be mitigated. 
Phoenix, Arizona is a a city of 1.46 million people. 
"The Phoenix metropolitan area has avoided a major water 
shortage this past year due to foresight of the Valley's water 
managers who, for the past 20 years, have been planning on how 
to address the inevitable drought," Manning says. "We are in 
better shape than most of the rest of the state, because we 
have four sources of water here in the Valley - pumped 
groundwater; surface water from the Salt, Verde, and Agua Fria 
rivers; Colorado River water; and reclaimed wastewater." 
Legal restrictions on the use of pumped groundwater has 
resulted in additional reliance on the Colorado River as a 
water supply source, Manning explains. 
"Here in central Arizona, we live in an area with the most 
progressive and rigorous groundwater code in the nation," he 
says. 
In central and southern Arizona and the Prescott area, 
"municipal water conservation programs are required, and new 
residential developments for which there is not a 100-year 
assured water supply from primarily non-groundwater sources 
are not allowed," Manning says. 
Since 1992, only low water use plumbing fixtures can be sold 
and installed in Arizona. These kinds of fixtures are used in 
all new construction and remodeling projects. 
"Over the years, millions of dollars have been spent 
constructing water treatment plants, installing pipelines, 
drilling wells, and developing underground storage projects," 
said Manning. 
Recently, the AMWUA has purchased water from the Central 
Arizona Project and stored it underground for recovery and use 
during a drought. 
"We are treating wastewater to as high a level as possible so 
that it can be used to recharge the Valley's aquifers and to 
irrigate golf courses, parks, and other turf facilities. In 
fact," said Manning, "the biggest nuclear power plant in the 
country, the Palo Verde Nuclear Generating Station, uses 
treated wastewater for cooling purposes." 
The Lamont-Doherty study, "Model projections of an imminent 
transition to a more arid climate in southwestern North 
America," is online at: 
http://www.sciencemag.org/sciencexpress/recent.dtl 

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