Influence of Clouds & FOG


fog bank engulfs central ridge

Wet soil beneath bishop pine from fog drip

Automated soil respiration chambers and met station

Fog event, Upem field site

Fog collector


Fog is a cloud that is in contact with the ground. Low-level marine stratus are the most common clouds forming fog.  Fog is often present in coastal California during May through August.  It occurs when the land warms in the spring and summer, and moist ocean air is pulled over cold coastal upwelling ocean waters. This moist air then condenses, creating low clouds or fog banks.  Santa Cruz Island is the largest of 8 Channel Islands. Located about 20 miles off the coast of Santa Barbara, CA, it is frequently inundated with low stratus and immersed in fog.

Related Sites:

UC Natural Reserve

The Nature Conservancy

Channel Islands National Park

CLoud water inputs & Plants:

Fog has been shown to be an important water source for plants in coastal CA.  It is often the only water input during the summer months because of the Mediterranean-type climate. During fog events, cloud water droplets accumulate on vegetation and drip to the ground significantly enhancing soil moisture (Ingraham & Matthews 1995; Corbin et al. 2005).  This fog drip is likely the largest water input to ecosystems from fog. However, fog and clouds are also important because they decrease evapo-transpirational losses from plants and soil by reducing net radiation and vapor pressure deficits (shading).

This project:

We are working at 2 field sites located in Bishop pine stands that have been shown to differ in the amount of fog and low-cloud cover (Fischer et al. 2007).  Despite the often months-long enhancement of soil moisture from fog, it is unclear (1) whether the additional fog-derived moisture stimulates summertime photosynthesis and stem and root growth by the conifer trees, or (2) whether it influences soil C cycling through effects on microbial dynamics, decomposition, and root respiration.  The study aims to understand how these summertime fog inputs versus wintertime rain inputs influence ecosystem C cycling and overall ecosystem function. This work includes automated, near-continuous measurements of soil respiration and evaporation, soil pore space CO2 concentrations, and sap flow, along with monthly measurements of pine growth, microbial biomass, soil nutrient availability, and isotopes of water and C. See Carbone et al (2011) Oecologia; Carbone et al (2013) Global Change Biology.

Field sites


Modis Images courtesy of nasa

Paired Sap flow and chamber measurements

Sap flow Probe set in a bishop pine  

Other island things:

Endemic island fox

spider webs are good fog collectoRS

In the Mediterranean-type climate of California, moisture inputs are almost exclusively derived from wintertime rain. In some coastal ecosystems, however, warm dry summers are ameliorated to some extent by fog and clouds.