California’s Fog is Clearing, and It’s Not Good

California’s Fog is Clearing, and It’s Not Good

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In the Central Valley, the fog is clearing.


A recent study published in the Geophysical Research Letters has shown that the average levels of winter Tule fog in California is dropping, negatively affecting the land that provides the US with 95 percent of its almonds, pistachios, cherries, apricots and peaches. Without fog, plants do not enter their natural dormant cycle. And without the cycle, they’re not protected.


“The trees need this dormant time to rest so that they can later develop buds, flowers and fruit during the growing season,” said biometeorologist and study lead author Dennis Baldocchi, whose father grew almonds and walnuts in Antioch and Oakley. “An insufficient rest period impairs the ability of farmers to achieve high quality fruit yields.”


During the winter time, California’s Central Valley is blanketed in both colder temperatures and “Tule Fog,” which is named after the grasslands from which the humidity comes. After studying the fog conditions over the last 32 winters, scientists have shown an an average drop of 46 percent in the number of fog days between the first of November and the end of February. Other studies have also shown there has also been a decline in the Central Valley of winter chill, or the number of hours between 0 and 7 degrees Celsius, and the number of hours of winter chill has dropped by several hundred since the 1950s, according to the study.


“The year-to-year variability we saw was likely influenced by whether the season was relatively wet or dry,” said Baldocchi. “Generally, when conditions are too dry or too wet, we get less fog. If we’re in a drought, there isn’t enough moisture to condense in the air. During wet years, we need the rain to stop so that the fog can form.”


Less fog and warmer temperatures mean plants aren’t reaching their dormant period, and therefore, buds are not protected and the germination process is thrown from its natural cycle. Baldocchi said that these drops are expected to continue, and therefore, farmers should start looking elsewhere.


“Farmers may also need to consider adjusting the location of orchards to follow the fog, so to speak,” said Baldocchi. “Some regions along the foothills of the Sierra are candidates, for instance. That type of change is a slow and difficult process, so we need to start thinking about this now.”


You may not like the Tule fog when you’re driving, but if you like almonds, pistachios, and fruits of California, you might change your mind.



FEATURED PHOTO: Anita Ritenour/Flickr

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