Fog, fog drip, and streamflow in the Santa Cruz Mountains of the California Coast Range

The onshore movement of marine fog is a common occurrence during summer months along much of the contiguous US Pacific Coast. Because the fog season tends to occur during the precipitation-free dry season, any additional input of moisture or reduction in loss of moisture through evapotranspiration provided by the marine layer can be an important factor in local hydrologic systems. To quantify some of the effects of fog on regional dry-season hydrology, a study site within the Santa Cruz Mountains of central California was established. The fog-laden coastside and predominately fog-free San Francisco Bay side of the study area provide an excellent opportunity to assess the impacts of the presence and absence of fog on ecohydrological processes. Streamflow, fog drip, and soil moisture were measured from May to September. Fog drip was essentially nonexistent on the bayside and highly variable on the coastside. Maximum rates and seasonal totals of drip occurred within stands of mature conifers (Sequoia sempervirens and Pseudotsuga menziesii) along exposed, often windy ridgelines. Fog-drip totals up to 961mm were recorded over 25months. Consequently, frequent infiltration events to depths of 23cm were documented. Over the course of the study, soil moisture levels at high-fog-drip locations either increased or were equivalent to spring conditions at the onset of data collection. Increases of flow in coastside streams, under otherwise receding conditions, were found to coincide with fog and fog-drip events. These results confirm that the presence of fog can significantly affect dry-season hydrologic conditions of some coastal locations. Copyright (c) 2014 John Wiley & Sons, Ltd.