Fog and live fuel moisture in coastal California shrublands

Abstract

9Across most Mediterranean-type climate regions, seasonal drought desiccates plants, facilitating ignition 10 and the spread of wildfires. Along the California coast, summertime fog has the potential to ameliorate 11 drought conditions and thus reduce plant flammability during a critical time of elevated fire risk. This 12 study investigated the uptake of dry season fog and how it affects live fuel moisture in six dominant shrub 13 species from chaparral and sage scrub plant associations. Fog water uptake was evaluated using stable 14 isotopes of hydrogen and oxygen at several field sites in Santa Barbara County, California. Clear 15 evidence of fog water uptake was identified only in Baccharis pilularis, from the sage scrub association. 16To determine the effects of fog on live fuel moisture, meteorological variables and indices including fog 17 deposition were combined into principal components and the scores regressed against the live fuel 18 moisture loss rate during the summer drought. Fog deposition slowed rates of live fuel moisture loss for 19all three sage scrub species tested, but it did not affect the chaparral species. Fog is a more regular 20 occurrence in the sage scrub association and thus it is likely that fog ameliorates drought for species that 21 experience consistent fog during the summer months. In coastal California, summer fog can be essential 22 to plant water relations and reduce live fuel moisture loss rates during the summer drought. 23

Effect of Reduced Summer Cloud Shading on Evaporative Demand and Wildfire in Coastal Southern California

“…Stratus clouds provide vital shade and occasional direct moisture deposition for coastal vegetation during the rain‐free warm season on North America's west coast (Baguskas et al, ; Dawson, ; Emery et al, ; Fischer et al, ; Iacobellis & Cayan, ; Williams et al, ). Coastal stratus clouds form within the cool and humid marine boundary layer and are most frequent during the warm season when synoptic frontal disturbances are infrequent, northerly winds promote coastal upwelling of cold water, and subsiding warm air on the east side of the North Pacific High enforces stability aloft (Clemesha et al, ; Wood, ).…”

Spatial Patterns and Trends of Summertime Low Cloudiness for the Pacific Northwest, 1996–2017

“…By the end of the 21st century, PNW summers are projected to be drier and hotter (Mote & Salathé, 2010), more closely resembling present‐day northern California (Fitzpatrick & Dunn, 2019). During coastal California's summers, low clouds regulate land surface temperatures (Iacobellis & Cayan, 2013), provide shade and supplemental moisture for native vegetation (Carbone et al, 2013; Fischer et al, 2009; Johnstone & Dawson, 2010; Williams et al, 2008), improve agricultural water use efficiency (Baguskas et al, 2018), reduce wildfire potential (Emery et al, 2018; Williams et al, 2018), maintain healthy stream levels (Sawaske & Freyberg, 2015), and modulate heat waves (Clemesha et al, 2018). Similar effects likely occur in the PNW.…”