Pacific Dictates Droughts and Drenchings
January 28, 2004
The cooler and drier conditions in Southern California over the last
few years appear to be a direct result of a long-term ocean pattern
known as the Pacific Decadal Oscillation, according to research
presented recently at the 2004 meeting of the American Meteorological
Society.
The study by Steve LaDochy, associate professor of geography at
California State University, Los Angeles; Dr. Bill Patzert, research
oceanographer at NASA's Jet Propulsion Laboratory in Pasadena,
Calif.; and others, suggests Pacific oceanic and atmospheric
measurements can be used to forecast seasonal West Coast temperatures
and precipitation up to a year in advance, from Seattle to San Diego.
An important climate controller, the Pacific Decadal Oscillation is a
basin-wide oceanic pattern similar to El Niño and La Niña but much
larger. The pattern lasts many decades rather than just a few months
like El Niño and La Niña. The climatic fingerprints of the pattern
are most visible in the North Pacific and North America, with
secondary influences coming from the tropics. The long-term nature of
the pattern makes it useful for forecasting, as its effects persist
for so long.
Since mid-1992, NASA has been able to provide space-based, synoptic
views of the entire Pacific Ocean and its shifts in heat content
through the Topex/Poseidon mission and its follow-up mission, Jason
(which began in 2001). Before these satellites were available,
monitoring oceanic climate signals in near-real time was virtually
impossible.
The remarkable data and images can tag and monitor the shifts in
short-term climate events, like El Niño and La Niña, and long-term
events such as the Pacific Decadal Oscillation. These data provide a
13-year continuous, complete time-series of two major El Niños and
two La Niñas, and have made it possible to detect a major phase shift
of the Pacific Decadal Oscillation. Patzert and LaDochy show that
these data, when combined with longer-term studies of land-based
data, provide a powerful set of forecasting tools.
The pattern shifted to a negative, cool phase, leading to wetter
conditions in the U.S. Pacific Northwest, and drier than normal
conditions in Central and Southern California this decade. Since the
last El Nino in 1997-1998, the Los Angeles area has had only 79
percent of its normal rainfall, Patzert said. Lake Mead, the great
fresh-water reservoir in southeast Nevada, is at less than 50 percent
of normal capacity. Also, huge West Coast fires over the past few
years have been greatly exacerbated by drought induced by the
pattern, Patzert added.
"These shifts in the pattern are long-term tendencies, which actually
have a bigger economic impact than El Niño," said Patzert. "People
talk about floods from El Niño, but what really has a harsh and
costly impact is a five-year drought."
"A full cycle of the Pacific Decadal Oscillation (cool to warm and
back to cool) runs about 50 years," said LaDochy. "Over the next
several years there is going to be a tendency toward dry and colder
temperatures in the southern U.S. West Coast. It is very difficult to
forecast day-to-day here on the West Coast, but we can say with some
confidence that over the next five years, we'd better start saving
water."
The researchers used more than 50 years of U.S. climatic information,
and Pacific atmospheric and oceanic data from the National Oceanic
and Atmospheric Administrations National Centers for Environmental
Prediction. By comparing data, they saw strong correlations between
Pacific climate patterns, temperatures and precipitation trends on
the West Coast. They then were able to develop "hindcasts" to explain
temperature and precipitation variability for West Coast regions.
These decadal cycles also will be useful for explaining future
regional climate variability.
NASA's Earth Science Enterprise is dedicated to understanding the
Earth as an integrated system and applying Earth System Science to
improve prediction of climate, weather and natural hazards using the
unique vantage point of space.
For more information and images about the research on the Internet,
visit:
http://www.gsfc.nasa.gov/topstory/2004/0116westcoast.html.
JPL is managed for NASA by the California Institute of Technology in
Pasadena.
