Posts Tagged: Hyunok Lee
Rising temperatures appear to be reducing the number of hours tree crops in the San Joaquin Valley are subjected to chill during the winter, a critical factor in producing a profitable yield, reported Ezra David Romero on Valley Public Radio, KVPR-FM.
Pistachios, for example, require temperatures between 32 and 45 degrees for about 700 hours each winter, but for the past four years have had less than 500 chill hours.
UC Davis researcher Hyunok Lee recently published a study about climate change impacts on agriculture in UC Agriculture and Natural Resources' peer-reviewed journal California Agriculture. The study found that winter temperatures are increasing more than any other time of year. Her modeling looks at the year 2050 in Yolo County.
“Our agriculture will continue,” Lee said. “But if you look at . . . like 20 years or 30 years. The pattern may change a little bit, crops may move a little bit north.”
Romero spoke to UC Cooperative Extension farm advisor Craig Kallsen, who holds the UC Cooperative Extension Presidential Chair for Tree Nut Genetics. Kallsen is conducting trials aimed at finding pistachio varieties with novel nut, tree growth and yield characteristics, and varieties that produce a high yield even under low-chill conditions.
"We're trying to use the other species of pistachios actually to see if we can come up with something that has a low chill requirement. It's pretty hypothetical at this stage,” Kallsen told Romero. “We made quite a few crosses this spring and we actually hope to put a trial in a low chill area.”
David Doll, UC Cooperative Extension farm advisor in Merced County, is studying other tactics to improve winter chill, such as using overhead sprinklers to cool the trees and painting them white with liquid clay to reflect sunlight.
"So this is something that could impact a lot of farmers over the next 10, 20, 30 to 40 years,” Doll said. “And in fact it's already impacting farmers on random given years across the state."
Of 12 crops examined in Yolo County, walnuts are most vulnerable, while processing tomatoes and alfalfa acreage may increase due to warmer winters.
In an effort to forecast how climate change may affect agriculture, University of California agricultural economists looked at how climate has affected crop acreage in the past. The effect of temperature changes on plants depends on local conditions and the crops grown. In a case study of Yolo County agriculture, warmer winter temperatures would reduce chill hours, potentially reducing yields for some crops while extending the growing season for others, according to a University of California study published in the peer-reviewed journal California Agriculture.
This technique used in Yolo County could be used for projecting the effects of climate change on agriculture in other regions, said Lee.
Using about 100 years of climate data and 60 years of farm acreage, Lee and her co-author looked at the relationships between the evolution of local climate conditions and the acreage of 12 major crops grown in Yolo County. The crops included processing tomatoes, rice, alfalfa, wheat, corn, prunes, grapes, walnuts, almonds, safflower, pasture and other fruit.
“When we look at maximum and minimum temperatures, the minimum temperatures are higher while the maximum temperature stays about the same,” Lee said. “And the lower temperature is rising at a faster rate, especially in winter. That's good for winter crops, but not so good for crops that require chill hours.” Many tree crops require cold for a certain number of hours below a critical temperature, commonly 45 degrees Fahrenheit, to stimulate the growth of leaves and flowers.
Among trees and vines, the most sensitive to climate change are walnuts, which require more chill hours. Walnut acreage would decline, Lee said, while there would be a modest change in grape and almond acreage.
Lee emphasized that market conditions exert a great deal of influence on the crops growers choose to plant. Growers who consider trends in climate change may choose different cultivars rather than different crops, such as a walnut variety that requires fewer chilling hours.
Lee and co-author Daniel Sumner, director of the UC Agricultural Issues Center and Frank H. Buck, Jr. Professor in the Department of Agricultural and Resource Economics at UC Davis, based their acreage projections on following the trend of climate change for the past 105 years, but were not able to incorporate climate variability, extreme weather events, accelerated warming or availability of irrigation water in their modeling.
This research, which was part of a larger study of climate change and agriculture funded by a grant from the California Energy Commission, was also supported by the UC Agricultural Issues Center, a program of UC Agriculture and Natural Resources.