Mathematical modeling of fog water deposition, San Francisco, California

Fog drip is a liquid form of occult precipitation that occurs when fog moves through vegetation and fog droplets are deposited on the vegetative surfaces and the water drips to the ground. Fog drip is an important hydrologic input to many ecosystems, including those in the San Francisco Bay Area where a number of studies have quantified fog drip and fog deposition from manmade collectors, which are a good approximation of fog drip. This is the first study to examine the correlation between meteorological conditions during advection fog episodes in the San Francisco Bay Area as well as fog deposition volume and stable isotopic composition. Meteorological data and fog deposition samples from a standard fog collector (SFC) and harp design were collected for a three-month period (2012) at a coastal site in Fort Funston, which is part of the Golden Gate National Recreation Area. Fog deposition samples from the SFC and harp collector were not significantly independent with mean 5D and 5I80 values, -13.74 (standard deviation 0.80) and -2.63 (standard deviation 0.15), respectively. These results support the important finding that fractionation of fog deposition is not a function of fog collector design. Meteorological data, fog deposition volume, and isotopic composition were used to construct multivariate linear regression models. Fog deposition volume strongly correlated with event duration, relative humidity, temperature, and wind direction, while isotopic composition strongly correlated with relative humidity and wind direction data.