Weathering Climate Change and Variability
by David Pescovitz
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UC
Berkeley Civil and Environmental Engineering professor
John Dracup believes the biggest breakthroughs in hydrologic
forecasting will come from his students who are only now beginning
their research careers.
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While we watch weather reports to decide if we need to carry an umbrella, the managers of California's water resources have much more invested in accurate climate forecasts. From subtle changes in snowfall to dramatic events like El Nino, climate fluctuations dramatically impact how much water is available to irrigate crops. That's why
UC Berkeley Civil and Environmental Engineering professor John
Dracup is helping water managers better predict the future.
"Understanding the impact and making accurate forecasts about
whether certain events may occur in a given season can help us
improve
the operation of our dams, reservoirs, and water systems."
The aim is to gain insight into the hydrologic implications of
global climate variables on stream flow. For example, in the western
United States, water managers consider the expected flow of this
surface water through the Columbia River basin, along with predicted
snowfall and other factors, to determine how much water to keep
in storage for the coming irrigation season. Currently, operators
base their decisions on mean data from previous years. But this
does not take into account the major deviations that may occur.
According to Dracup, there are two kinds of climate events that
have the most potential to alter stream flows. The first, climate
variability, refers to natural shifts in temperature in the tropical
Pacific Ocean that don't happen with any regularity from year to
year. The best-known of these events is the El Nino-Southern Oscillation,
or ENSO. In the 1990s, Dracup and his colleagues studied the impact
of ENSO on rainfall. The particularly strong effect of ENSO in
eastern Australia and the western United States enabled Dracup
to demonstrate an improved method to forecast stream flows six
months in advance.
More recently, Dracup has immersed himself in the Pacific Decadal
Oscillation (PDO), an ENSO-like pattern of Pacific climate variations
first observed in 1996. The main difference between the two is
that PDO events may persist as long as three decades as compared
to ENSO's six to eighteen months.
"We'd eventually like water managers to incorporate these
long-term variabilities in their operational decisions, for example
how much
water they store or allocate for irrigation," Dracup says. "But
we need to give them probabilities of, say, whether it will be
drier or wetter than usual in the coming year."
Another focus of
Dracup's work is to tease apart climate variability from climate
change, a continuous shift in temperature. For example,
global warming may be an example of climate change but, Dracup
says, "the jury is still out on that one." Only by differentiating
between climate variability and climate change can better models
be developed to determine how the phenomena will impact agricultural
production, for example, or the salinity of rivers that yield drinking
water. Drawing from observations of the geophysical record, as
melting glaciers, global circulation models, and scenarios based
on those models, Dracup hopes to reveal how climate change and
variability may be related.
"To study these things, we use computer simulation models
that reproduce the essence of a system without reproducing the
entire system itself," he
explains.
Yet the simulations are only as good as the data fed into them.
That's why, Dracup believes, the biggest breakthroughs in hydrologic
forecasting will come from his students who are only now beginning
their research careers.
"Climate variability and climate change have been occurring
for thousands of years but people have only recently begun observing
them," Dracup says. "Twenty years from now, scientists
will have a lot more data to study."
John Dracup's Home Page
Institute for Environmental Science and Engineering (IESE)
Lab Notes is
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© 2003 UC Regents.
Updated 11/30/03.
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