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

Redwoods poorly regulate their water use, and thus are highly sensitive to humidity. Without summer fog, redwoods can lose too much water through their leaves by transpiration and suffer drought stress. (James Johnstone/UC Berkeley) BERKELEY — 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. "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.