California's Central Valley is one of the most productive agricultural regions in the world, with some 230 crops grown there. Heat waves are costly for the region and its residents. File Photo by Ken Lund/Wikimedia Commons https://creativecommons.org/licenses/by-sa/2.0/deed.en

April 12 (UPI) -- Californians may want to start watching the forecast in Southeast Asia.

When heavy rains fall on the tropics in the Indian and the eastern Pacific oceans, temperatures across California increase some 16 days later, according to a new study.


California's Central Valley is one of the most productive agricultural regions in the world, with some 230 crops grown there. The region's farms and orchards produce half of the nation's tree fruit and nut crops. Heat waves are costly for the region and its residents.

"We want to know more about how extreme events are created," Richard Grotjahn, professor at the University of California, Davis, said in a news release. "We know that such patterns in winter are sometimes linked with areas of the tropics where thunderstorms are enhanced. We wondered if there might be similar links during summer for those heat waves."

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When scientists surveyed data collected by 15 National Climatic Data Centers stations between 1979 to 2010, they identified 24 Central Valley heatwaves during that time span. Researchers compared the timing of California's heat waves with the timing of an atmospheric circulation pattern known as the Madden-Julian Oscillation, or MJO.

The MJO pattern produces large amounts of rain and thunderstorms that move across the tropical Indian and eastern Pacific oceans.

Researchers found a consistent and predictable pattern -- a strong link between the Southeast Asian atmospheric pattern and rising temperatures in California. Some two weeks after heavy rains travel across the tropics of Southeast Asia, a heat wave spreads across the Central Valley.

The new analysis, published this week in the journal Advances in Atmospheric Sciences, also showed stronger MJO storms trigger more intense heatwaves.

"The more we know about such associations to large-scale weather patterns and remote links, the better we can assess climate model simulations and therefore better assess simulations of future climate scenarios," Grotjahn said.