[North-NV-Greens] Fwd: Global Warming Key Factor in Drought's Global Reach

[Paul Etxeberri]

>
>
>Drought's Growing Reach:
>NCAR Study Points to Global Warming as Key Factor
>
>January 10, 2005
><http://www.ucar.edu/news/releases/2005/drought_research.shtml>
>
>BOULDER- The percentage of Earth's land area stricken by
>serious drought more than doubled from the 1970s to the
>early 2000s, according to a new analysis by scientists
>at the National Center for Atmospheric Research (NCAR).
>Widespread drying occurred over much of Europe and Asia,
>Canada, western and southern Africa, and eastern
>Australia. Rising global temperatures appear to be a
>major factor, says NCAR's Aiguo Dai, lead author of the
>study.
>
>Dai will present the new findings on January 12 at the
>American Meteorological Society's annual meeting in San
>Diego. The work also appears in the December issue of
>the Journal of Hydrometeorology in a paper also authored
>by NCAR's Kevin Trenberth and Taotao Qian. The study was
>supported by the National Science Foundation, NCAR's
>primary sponsor.
>
>Dai and colleagues found that the fraction of global
>land experiencing very dry conditions (defined as -3 or
>less on the Palmer Drought Severity Index) rose from
>about 10-15% in the early 1970s to about 30% by 2002.
>Almost half of that change is due to rising temperatures
>rather than decreases in rainfall or snowfall, according
>to Dai.
>
>"Global climate models predict increased drying over
>most land areas during their warm season, as carbon
>dioxide and other greenhouse gases increase," says Dai.
>"Our analyses suggest that this drying may have already
>begun."
>
>Even as drought has expanded across Earth's land areas,
>the amount of water vapor in the air has increased over
>the past few decades. The average global precipitation
>has also risen slightly. However, as Dai notes, "surface
>air temperatures over global land areas have increased
>sharply since the 1970s." The large warming increases
>the tendency for moisture to evaporate from land areas.
>Together, the overall area experiencing either very dry
>or very wet conditions could occupy a greater fraction
>of Earth's land areas in a warmer world, Dai says.
>
>Though most of the Northern Hemisphere has shown a
>drying in recent decades, the United States has bucked
>that trend, becoming wetter overall during the last 50
>years, says Dai. The moistening is especially notable
>between the Rocky Mountains and Mississippi River. Other
>parts of the world showing a moistening trend include
>Argentina and parts of western Australia. These trends
>are related more to increased precipitation than to
>temperature, says Dai
>
>>   [Go to the source link above to see the illustration
>>   that this caption accompanies. -- moderator]
>>
>>   This depiction of linear trends in the Palmer Drought
>>   Severity Index from 1948 to 2002 shows drying (reds
>>   and pinks) across much of Canada, Europe, Asia, and
>>   Africa and moistening (green) across parts of the
>>   United States, Argentina, Scandinavia, and western
>>   Australia. (Illustration courtesy Aiguo Dai and the
>>   American Meteorological Society.)
>
>"Droughts and floods are extreme climate events that are
>likely to change more rapidly than the average climate,"
>says Dai. "Because they are among the world's costliest
>natural disasters and affect a very large number of
>people each year, it is important to monitor them and
>perhaps predict their variability."
>
>To see how soil moisture has evolved over the last few
>decades, Dai and colleagues produced a unique global-
>scale analysis using the Palmer index, which for decades
>has been the most widely used yardstick of U.S. drought.
>The index is a measure of near-surface moisture
>conditions and is correlated with soil moisture content.
>
>Since the Palmer index is not routinely calculated in
>most of the world, Dai and colleagues used long-term
>records of temperature and precipitation from a variety
>of sources to derive the index for the period 1870-2002.
>The results were consistent with those from a historical
>simulation of global land surface conditions, produced
>by a comprehensive computer model developed by
>scientists at NCAR, NASA, Georgia University of
>Technology, the University of Texas at Austin, and the
>University of Arizona.
>
>By factoring out rainfall and snowfall, Dai and
>colleagues estimated how much of the global trend in
>soil moisture was due solely to rising temperatures
>through the extra evaporation they produce.
>
>"The warming-induced drying has occurred over most land
>areas since the 1970s," says Dai, "with the largest
>effects in northern mid and high latitudes." In
>contrast, rainfall deficits alone were the main factor
>behind expansion of dry soils in Africa's Sahel and East
>Asia. These are regions where El NiÒo, a more frequent
>visitor since the 1970s, tends to inhibit precipitation.
>
>---
>
>The National Center for Atmospheric Research and UCAR
>Office of Programs are operated by UCAR under the
>sponsorship of the National Science Foundation and other
>agencies. Opinions, findings, conclusions, or
>recommendations expressed in this publication do not
>necessarily reflect the views of any of UCAR's sponsors.
>
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-- 
Paul Etxeberri

"Forests precede civilizations and deserts follow"   ---Chateaubriand