The Central Valley’s heavy wintertime tule fog – known for snarling traffic and closing schools — has been on the decline over the past 30 years, and falling levels of air pollution are the cause, says a new study by scientists at the University of California, Berkeley.
Tule fog, named for a sedge grass that populates California’s wetlands, is a thick ground fog that periodically blankets the Central Valley during the winter months.
To find out why the fog is fading, the researchers analyzed meteorological and air pollution data from the Central Valley reaching back to 1930. They found that while yearly fluctuations in fog frequency could be explained by changes in annual weather patterns, the long-term trends matched those of pollutants in the air.
The results help explain the puzzling decades-long rise and fall in the number of “fog days” affecting the region, which increased 85 percent between 1930 to 1970 and then decreased 76 percent between 1980 to 2016. This up-and-down pattern follows trends in air pollution in the valley, which rose during the first half of the century, when the region was increasingly farmed and industrialized, and then dropped off after the enactment of air pollution regulations in the 1970s.
Read more at University of California, Berkeley
Photo: NASA’s Terra – MODIS satellite captures a thick blanket of fog covering California’s Central Valley. (NASA photo by Jeff Schmaltz)