By Betsy Mason
CONTRA COSTA TIMES
New research suggests that
irrigation has kept croplands cool, essentially countering rising temperatures
caused by greenhouse gas emissions over the last half century. But in the
future, global warming will win out and agricultural areas will see hotter
temperatures.
"When you irrigate the land
it causes cooling that is almost equal in magnitude to the global warming
effect," said climate scientist Lisa Sloan of UC Santa Cruz. "Changing
the land surface can change regional climate a lot."
And the impact may be compounded
by the predicted decreases in water available for agriculture in the state due
to global warming. This in turn would cause more reductions in water supply,
which would further restrict irrigation.
"If our water gets cut back
and we stop irrigating, suddenly we could double the warming," Sloan said
at the Climate Change Conference in
The cooling from irrigation
explains why computer models that simulate climate were consistently
overestimating past summer temperatures in agricultural areas, researchers said
Thursday.
"The fact that irrigation
has a strong effect on summer temperatures helps us understand why our models
were wrong," said climate scientist David Lobell of Lawrence Livermore
Laboratory, who also studies the effect of irrigation on climate. When
irrigation is accounted for in these models, they come much closer to the actual
recorded summer temperatures in these areas.
But winter temperatures have been
rising as expected, which is causing problems for some farmers who complain of
changes such as a decrease in the number of "chill hours" below 45
degrees that fruit trees need to flower.
Biological meteorologist Dennis
Baldocchi of UC Berkeley looked at temperature records for several agricultural
areas in the state, including the
"In
Once global warming overcomes the
cooling effect of irrigation, summer crops will begin having serious problems as
well.
"It's been suppressed and
held back by irrigation," said Lobell of Livermore Lab. "But in the
future that constraint on temperature won't be there anymore."
Reach Betsy Mason at bmason@cctimes.com
or 925-847-2158.
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Source:
http://www.contracostatimes.com/mld/cctimes/news/15521350.htm