How much does dry-season fog matter? Quantifying fog contributions to water balance in a coastal California watershed

Michaella Chung, Alexis Dufour, Rebecca Pluche, Sally Thompson

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


The seasonally-dry climate of Northern California imposes significant water stress on ecosystems and water resources during the dry summer months. Frequently during summer, the only water inputs occur as non-rainfall water, in the form of fog and dew. However, due to spatially heterogeneous fog interaction within a watershed, estimating fog water fluxes to understand watershed-scale hydrologic effects remains challenging. In this study, we characterized the role of coastal fog, a dominant feature of Northern Californian coastal ecosystems, in a San Francisco Peninsula watershed. To monitor fog occurrence, intensity, and spatial extent, we focused on the mechanisms through which fog can affect the water balance: throughfall following canopy interception of fog, soil moisture, streamflow, and meteorological variables. A stratified sampling design was used to capture the watershed's spatial heterogeneities in relation to fog events. We developed a novel spatial averaging scheme to upscale local observations of throughfall inputs and evapotranspiration suppression and make watershed-scale estimates of fog water fluxes. Inputs from fog water throughfall (10-30mm/year) and fog suppression of evapotranspiration (125 mm/year) reduced dry-season water deficits by 25% at watershed scales. Evapotranspiration suppression was much more important for this reduction in water deficit than were direct inputs of fog water. The new upscaling scheme was analyzed to explore the sensitivity of its results to the methodology (data type and interpolation method) employed. This evaluation suggests that our combination of sensors and remote sensing allows an improved incorporation of spatially-averaged fog fluxes into the water balance than traditional interpolation approaches.

Original languageEnglish
Pages (from-to)3948-3961
Number of pages14
JournalHydrological Processes
Issue number22
Publication statusPublished - 30 Oct 2017
Externally publishedYes


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