Coastal Los Angeles losing fog to urban sprawl

Morning fog along parts of coastal Southern California is disappearing due to nearby urbanization, new research suggests.

Since 1948, fog frequency has plummeted 63 percent in the Los Angeles area, bioclimatologist A. Park Williams of Columbia University and colleagues report in a paper to be published in Geophysical Research Letters. Portions of San Diego also saw decreases. Fog around Santa Barbara and offshore islands remained relatively unchanged.

Williams and colleagues collected weather observations from 24 airfields along the Southern California coast. Using 1950 census data and modern-day maps, the researchers discovered that at airfields where fog frequency fell, significant amounts of urbanization had taken place within a 10-kilometer radius. Building materials such as concrete absorb heat during the day and radiate the stored energy overnight, raising nighttime temperatures. The heat prevents water from condensing near ground level, so fog can’t form.

Coastal fog is an important climate component that curbs water evaporation and moderates temperatures. So decreased fog frequency could worsen drought conditions and result in hotter summertime temperatures, the researchers note. Yet there is a silver lining in these missing clouds: Fog is a major cause of traffic accidents in the region.