It has been
raining for days in the Triangle, but state climatologist
Sethu Raman has drought on his mind. Evidence is mounting, he
says, that a recently identified cooling pattern in the
Pacific Ocean could prolong drought conditions in this region
for another seven years, especially in the western part of
North Carolina.
"The public often feels that things are going to be OK if
we get a couple of days of rain in a row," he said. "They
don't understand."
This pattern, called the cool phase of the Pacific Decadal
Oscillation, occurs when central and eastern Pacific waters
near the equator become cooler than their average temperature.
That shifts the jet stream that travels over North America to
the north, pushing many rain-carrying storms away from the
Southeast.
"If it persists for more than a few years, which it
typically does, then we could be in for a prolonged period of
much-lower-than-normal precipitation statewide, particularly
in western North Carolina in the summer," said Raman,
professor of meteorology at N.C. State University and director
of the State Climate Office.
"Municipalities would be well advised to plan for long-term
water use and conservation measures now," he said.
Meteorologists did not know about the PDO, which can last a
decade, until the 1990s. A fisheries scientist gave a name to
the pattern in 1996 when studying the connection between
Alaska salmon populations and the Pacific climate.
Now scientists are tracking its effects in the past by
studying Pacific water temperature trends and rainfall
records. Raman's office, for one, is analyzing 100 years of
data from weather stations across the state to better assess
the effects of PDO. North Carolina has suffered drought
conditions since 1998.
Research by the State Climate Office so far shows that
cool-phase PDOs occurred in the 1920s, 1950s and 1980s, when
this state had some of its driest periods, he said.
In the meantime, a cooling of Pacific waters has been
observed since 1998, indicating that below-normal rainfall,
averaging four to six inches during 1998, 1999 and 2000, could
be linked to the Pacific water shifts, Raman said. North
Carolina's rainfall remained lower than average despite the
heavy rain from hurricanes Bonnie, Dennis, Floyd and Irene in
1998 and 1999.
It is such hurricanes, or tropical storms, that could
protect the eastern part of North Carolina from the worst of
the drying phase to come, Raman said. In fact, forecasters
expect that the Southeast could see a higher number of
tropical storms in coming years as a result, in part, of
higher-than-average water temperatures in portions of the
Atlantic.
So far, the central and western part of North Carolina has
felt the drought's effects more than the East, said Tony
Young, chairman of the state's Drought Monitoring Council.
Several communities have had to ask, sometimes even require,
residents to use less water. Forty water systems statewide
called for water use restrictions during 1999. Greensboro and
Asheville are among the communities that have been hit
hardest.
Drought, which Raman describes as a deficit of 4 to 12
inches of rain a year in a state that usually soaks up 50
inches, affects more than people's abilities to keep their
grass pretty during a scorching Tar Heel summer. Drought can
slow production on farms and in factories, which use water to
cool equipment or process waste. It drops stream levels. And
it can leave undeveloped areas vulnerable to fire, Young said.
"March was a nice, wet month," Young said. "It brought some
good short-term relief. Whether that's enough to provide
relief for the long term, we don't know."
Raman, who comes from a dry region in India where people
sometimes must spend more for water than for food, wants to
get word out on the PDO so people understand that larger
trends are shaping the weather they encounter each day. That
way people can better plan for the long term, he said.
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