[permaculture] [Fwd: Long-Term Droughts in U.S. Linked to to Ocean Temperature Variations in North Pacific and North Atlantic]
Lawrence F. London, Jr.
lfl at intrex.net
Wed Mar 10 04:04:28 EST 2004
From: Catherine E Puckett [mailto:catherine_puckett at usgs.gov]
Sent: Tuesday, March 09, 2004 12:18 PM
Subject: USGS PRESS RELEASE: Research Links Long-Term Droughts in U.S. to
Ocean Temperature Variations in North Pacific and North Atantic
USGS, Western Region
Office of Communications
371 Redmond Rd.
Eureka, CA 95503
EMAIL: catherine_puckett at usgs.gov
U.S. Geological Survey
U.S. Department of the Interior
Date: March 9, 2003
Contact: Greg McCabe, 303-236-7278, gmmcabe at usgs.gov; Mike Palecki,
217-333-8506, palecki at uiuc.edu; Julio Betancourt, 520-670-6821, x107,
jlbetanc at usgs.gov
USGS Research Links Long-Term Droughts in U.S. to Ocean Temperature
Variations in the North Pacific and North Atlantic
Large-scale, long-lasting droughts in the United States -- such as the
present one in the West -- tend to be linked to warmer than normal sea
surface temperatures in the North Atlantic Ocean, and not just cooling in
the tropical Pacific, according to a USGS study published today in the
Proceedings of the National Academy of Sciences.
The study statistically associates the patterns of U.S. droughts during the
last century to multi-decade variations in North Pacific and North Atlantic
sea surface temperatures, said USGS lead author Gregory McCabe and his
co-authors, USGS scientist Julio Betancourt and Mike Palecki of the
Midwestern Regional Climate Center at the Illinois State Water Survey.
Although droughts remain largely unpredictable, McCabe suggests that "this
research, as well as that of others, "increases concern that the current
drought in the West could persist due to continuing above normal North
Atlantic sea surface temperatures." The focal region of the drought may
shift with the more variable North Pacific sea surface temperatures, he
The U.S. climate of the last century was marked by three prolonged
continental-scale wet spells (1905-1930, the 1940s, and 1976-1995) and
three dry spells (the 1930's, 1950s-60s, and 1996-2004). Although
researchers believe that such large and sustained shifts in U.S.
precipitation are linked with the natural variability of sea surface
temperatures, the mechanisms are not well understood and cannot yet be used
to help predict the likelihood of droughts.
These sea surface temperature variations are characterized by climatic
indices dubbed the Pacific Decadal Oscillation, or PDO, and the Atlantic
Multidecadal Oscillation, or AMO. The Pacific Decadal Oscillation, or PDO
index, reflects the geographic pattern of temperatures in the North Pacific
Ocean and the AMO reflects basinwide temperatures in the North Atlantic
Ocean. When the PDO is positive, temperatures of the central North Pacific
are cool and the eastern tropical Pacific Ocean is warm. When PDO is
negative, the central North Pacific is warm and the eastern tropical
Pacific is cool. A positive AMO indicates warm temperatures across the
entire North Atlantic Ocean and negative AMO indicates cool North Atlantic
Both negative and positive PDO "events" in the North Pacific Ocean tend to
last 20-30 years, with recent research increasingly associating these
events with regional temperature and precipitation variability across the
country. For example, most scientists think the PDO variability is linked
to changes in the frequency and duration of El Niño or La Niña events over
the course of decades.
The AMO association with U.S. climate is less well known, but recent
studies suggest that variation in water temperatures in the North Atlantic
affects summertime precipitation and could also regulate the strength of El
Niño/La Niña effects on weather year-round, particularly in the Midwest.
The statistical study was aimed at delineating temporal and geographical
variations in drought frequency and then correlating these variations with
indices of Pacific and Atlantic Ocean climate . The researchers were able
to correlate two of the three leading modes of drought frequency with PDO
and AMO variations. The other pattern of variability, the researchers
suggest, may represent a complex pattern of trends in drought frequency
related to increasing Northern Hemisphere temperatures, or some other
as-yet unidentified climate trend.
In general, McCabe and his coauthors suggest that large-scale droughts in
the United States are likely to be associated with positive AMO -- the kind
of warming of sea surface temperatures that occurred over the North
Atlantic in the 1930s, 50s, and since 1995.
In contrast, wet conditions prevail over most of the country during North
Atlantic cooling (negative AMO). The researchers found that cool waters in
the central North Pacific are associated with drought in the Northern
Rockies and Pacific Northwest, whereas warm waters in the central North
Pacific are generally associated with drought in the Southwest and
The researchers said that the best hope for predicting long-term droughts
seems to lie with identifying precursor states in oceanic climate that
could lead to drought. The authors noted that persistent and widespread
droughts can potentially compromise crop and livestock production, revenues
from outdoor recreation and tourism, international and interstate water
agreements, sustained urban growth, management of wildland fires, and even
conservation efforts nationwide.
"What we hope to do eventually," said Betancourt, "is use the information
on the relationship between sea surface temperatures and North American
climate to help resource managers and policy makers guide the country in
more effective and long-term water management strategies and to anticipate
climatic effects on ecosystems."
The USGS serves the nation by providing reliable scientific information to
describe and understand the Earth; minimize loss of life and property from
natural disasters; manage water, biological, energy, and mineral resources;
and enhance and protect our quality of life.
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