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Professor's Research Shows Irrigation Hides Global Warming Effects

February 8, 2007

MERCED, CA— The prevalence of irrigation
throughout California — especially in the Central Valley
— could mask the effects of global warming, a new research
paper indicates.

Professor Lara Kueppers, with the School of Natural Sciences at
UC Merced, said she and two colleagues from UC Santa Cruz began
looking at how irrigation’s natural cooling can affect mean
temperatures in certain areas.

What they found is that irrigation causes the mean temperature
in summer months to drop, even as greenhouse gas emissions drive
temperatures upward.

“It gives a false sense of security,” Kueppers said, “because
the irrigation makes it really difficult to assess the effects of
greenhouse gases.”

Kueppers and her colleagues used a computer model to look at
California, which essentially became a look at the Central Valley,
the state’s largest irrigated area.

Their model indicates that August’s mean temperature in
irrigated areas has dropped by about 6.5 degrees Fahrenheit, while
greenhouse gas emissions are expected to warm the Earth about the
same amount.

Kueppers’ paper has a major implication: activities related to
agriculture, forestry and development do matter to the climate, she said.

“If we don’t consider what we’re doing to the area by
urbanizing, which removes farmland that has a cooling effect, we
could very well end up with a much hotter Central Valley,” she said.

She and co-authors Mark A. Snyder and Lisa C. Sloan, of the
Climate Change and Impacts Laboratory, Department of Earth and
Planetary Sciences at UC Santa Cruz, said more research looking at
absolute temperatures — not using computer models — is
already under way at Lawrence Livermore National Laboratory.

“From what I’ve seen, their work is coming to similar
conclusions as ours,” Kueppers said.

The abstract of Kueppers’ paper can be viewed for free

. Geophysical Research Letters, published by The American
Geophysical Union, presents short research letters that offer
scientific advances likely to have immediate influence other
investigators’ research. It has been published since 1974.