Climate change could put the heat on California crops

LOS ANGELES TIMES. JULY 22, 2009. By Margo Roosevelt

Fruit and nut orchards in the Central Valley rely on winter chilling hours, but those are in decline, according to a UC Davis study.

The Lockes have tilled the rich soil along the Mokelumne River since 1850. Now Chris Locke, 57, looks forward to passing down his orchards of 40,000 walnut trees to his four sons.

But the threat of global warming has him worried. "I talk to my boys about climate change," he said. When he was young, frigid fogs rolled off the delta into Lockeford, the town named for his forebears. "We would go a week without seeing the sun. But we don't seem to get that weather anymore."

If San Joaquin Valley farmers such as Locke are fearful, so are the agricultural scientists who support California's $10-billion annual fruit and nut crop, the largest in the nation. A new study from UC Davis, to be published today, found that the number of winter chilling hours, essential to the flowering of orchards, has declined as much as 30% since 1950 in large swaths of the Central Valley, where most of the tree crops are grown.

Only 4% of the Central Valley is now suitable for apples, cherries and pears, all high-chill fruits that could once be grown in half the valley, according to the study. By the end of the century, it says, "areas where safe winter chill exists for growing walnuts, pistachios, peaches, apricots, plums and cherries are likely to almost completely disappear."

Winter chill hours could decrease 60% from 1950 levels by mid-century and by as much as 80% by the end of the century, according to the study.

"Climate change is not just about sea-level rise and polar bears," said UC Davis researcher Eike Luedeling, lead author of the study. "It is about our food security. Climate change may make conditions less favorable to grow the crops we need to feed ourselves."

The study comes amid a spate of reports predicting a decline in agriculture in California -- which produces half of the nation's domestic fruits, nuts and vegetables -- as climate change affects water supplies and growing seasons.

The UC Davis study, which is to appear in the journal PLoS One, builds on a 2007 paper by UC Berkeley scientists Dennis Baldocchi and Simon Wong that predicted dramatic drops in winter chilling hours. But it expands on that research using a variety of climate models, and maps the expected changes in detail.

"These maps directly communicate the devastating effects of climate change on tree crops in California," said co- author Minghua Zhang, a UC Davis professor of environmental and resource science.

Baldocchi endorsed the UC Davis study, remarking, "The irony is, just as the populace is getting more in tune with eating better, eating local, our wonderful fruit industry may be negatively affected."

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