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Warmer Temperatures Could Offer Californian Farmers A Rare Silver Plated: Less Frost

Few things affect where fruit and nut trees can thrive more than heat. Nuts and many fruit trees need enough cold hours to produce quality yields, whereas too much cold can result in disaster, especially at the wrong time.

Untimed frosts have caused California farmers to pay nearly $ 400 million in insurance for damages to perennial orchards over the past two decades. But the real cost of freezing is much higher because not all farmers carry insurance and yield losses will not cover all the money spent on preventing freezing.

Now, in news of a rare good climate for California farmers, a recent study suggests that orchards could see fewer crop destructive frosts by mid-century.

Frost damage has always been a risk for perennial tree crops that have passed through a growth-stopping type of hibernation to survive freezing temperatures. Farmers may lose the entire crop if a cold blow strikes the trees during their early flowering after a warm, non-seasonal winter drives them to disturb their sleep.

However, it was unclear whether such significant encounters between frosts and early bud break would become an unsustainable cost of business under climate change.

To find out, scientists from two University of California campuses and the U.S. Department of Agriculture have used climate models to understand how changes in temperature in the coldest winters will affect frost exposure and mitigation costs for $ 7 billion almonds, avocados, in the state. navel orange groves.

Scientists have compared past exposure to frost with predicted frost events, based on the most likely scenario for future emissions (using a scenario called RCP 8.5). According to the model, the coldest winter temperatures in California will warm more than 4.5 degrees Fahrenheit (2.5 Celsius) in most of the state by the middle of the century.

According to estimates published in the March issue of Science of the Total Environment and online in December, most almond and navel orange plantations will see a 50 to 70 percent decrease in frost exposure by the middle of the century, while avocado gardens will see at least 75 percent more. less freezing hours.

The study found that less frost in the growing region could save farmers billions of gallons of water and millions of dollars in energy costs to prevent frost damage.

Lauren Parker, co-author and postdoctoral fellow at the University of California at Davis and the USDA’s California Climate Center, will always be winners and losers with climate change, but the study pointed to a potential benefit.

Parker, who specializes in agricultural climate science, quickly points out that warmer winters can do more harm than good to long-lived crops, which could result in a reduction in required cold hours and more pests. “But despite all the bad news, it’s nice to be able to say that there is at least some silver lining at these warming temperatures,” he said.

A Costly War Against Frost

Almonds and navel oranges are particularly sensitive to frost. Battered almond trees that bloom earlier than normal after a bitterly cold, warm winter temperatures in 2018. Growers in the most affected areas received approximately $ 45 million from federal insurance payments for frost damage. Four years ago, a freezing cost cost $ 25 million to orange growers.

Most frosts in California occur on clear nights with little wind, when the heat spreads rapidly from the orchard as the sun sets. Cool, dense air sinks to the ground, while lighter warm air rises above the tree canopy.

Growers put in great effort and resources to reduce the risk of frost by using heaters, wind machines and jets to mix the layers of air and raise the temperature around the trees by a few degrees. Some growers even hired helicopter pilots to visit an orchard and blend the cold air hanging in the trees with the warmer air floating above the canopy, Parker said.

After the freeze in 2018, Parker spoke to a Sacramento Valley almond farmer who passed late at night to check the predicted freezing thermometers, wandering around orchards late at night, sometimes waking up at midnight. “He joked about all the coffees he drank during flowering season,” he said. I sent him coffee at Christmas for the next season.

Kripa Jagannathan, a postdoctoral research fellow in climate adaptation at the Lawrence Berkeley Lab and not involved in the research, said that a non-freezing season is both critical for trees and prolonged, providing valuable information for growers.

Five years ago, Jagannathan asked Central Valley almond growers what kind of climate change information would be most useful to them as part of his doctoral research. During flowering, frost effects were a major concern, as they could steal a large part of their annual income.

Jagannathan said a climate projection couldn’t tell growers how many times they should use sprinkler systems to reduce freezing by 2050. “But it helps them understand their regional climate and how it’s changing.”

The projected reduction in water and energy use from having less frost to manage is clearly a bonus, Parker said. “But it’s not all sunshine and roses.”

The water and energy used to reduce freezing are just part of what is needed during the growing season, he said. These demands are likely to increase as farmers face more frequent, severe and prolonged heatwaves. In addition, the same warming phenomenon, which will reduce the risk of frost, will reduce the cold hours required for proper fruit development, increase the reproductive capacity of pests, and reduce the Sierra Nevada snowpack that provides surface water irrigation.

Estimating how climate change might affect crops is complex, and results will vary based on crop, location, emission pattern and other factors. The study did not determine whether the plants would bloom earlier, but the previous study by Parker and a colleague found that climate change would pose a minimal risk of frost for California almonds, although new growth was expected to occur on average six days earlier. Until the middle of the century.

However, farmers will continue to see early blooms against frosts, Parker said. “Most of California’s orchards will have frosts, maybe less.”

Parker paused to consider what the results might mean for individual breeders. “I often think of Will,” he said, referring to his almond grower friend in Sacramento Valley. “He might not need that much coffee.”

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