Fog has declined in past century along California's redwood coast

ScienceDaily (Feb. 16, 2010) — California’s coastal fog has decreased significantly over the past 100 years, potentially endangering coast redwood trees dependent on cool, humid summers, according to a new study by University of California, Berkeley, scientists. It is unclear whether this is part of a natural cycle of the result of human activity, but the change could affect not only the redwoods, but the entire redwood ecosystem, the scientists say. “Since 1901, the average number of hours of fog along the coast in summer has dropped from 56 percent to 42 percent, which is a loss of about three hours per day,” said study leader James A. Johnstone, who recently received his Ph.D. from UC Berkeley’s Department of Geography before becoming a postdoctoral scholar in the campus’s Department of Environmental Science, Policy and Management (ESPM). “A cool coast and warm interior is one of the defining characteristics of California’s coastal climate, but the temperature difference between the coast and interior has declined substantially in the last century, in step with the decline in summer fog.” The loss of fog and increased temperature mean that “coast redwood and other ecosystems along the U.S. West Coast may be increasingly drought-stressed, with a summer climate of reduced fog frequency and greater evaporative demand,” said coauthor Todd E. Dawson, UC Berkeley professor of integrative biology and of ESPM. “Fog prevents water loss from redwoods in summer, and is really important for both the tree and the forest. If the fog is gone, we might not have the redwood forests we do now.” The scientists’ report will be posted online during the week of Feb. 15 in advance of publication in the journal Proceedings of the National Academy of Sciences. The surprising result came from analysis of new records recently made available by the National Climate Data Center. The U.S. Surface Airways data come from airports around the country, which have recorded for more than 60 years hourly information such as cloud cover (cloud ceiling height), visibility, wind and temperature. … “This is the first data actually illustrating that upwelling along the Pacific coast and fog over the land are linked,” Johnstone said. … “The data support the idea that Northern California coastal fog has decreased in connection with a decline in the coast-inland temperature gradient and weakening of the summer temperature inversion,” Johnstone said. “As fog decreases, the mature redwoods along the coast are not likely to die outright, but there may be less recruitment of new trees; they will look elsewhere for water, high humidity and cooler temperatures,” Dawson said. “What does that mean for the current redwood range and that of the plants and animals with them?” …

Fog has declined in past century along California’s redwood coast