Drought may not be the right time to be thinking about this, or maybe it is. It concerns managing water and any time a grower uses water more effectively the crop performs better. But fog can be a significant factor in water management.
As fog passes through a tree canopy, it is absorbed by leaves and coats them. Before the tree will transpire water, the water coating must first be evaporated before the tree loses internal water. This water use is not accounted for in a water budget schedule using evapotranspiration based inputs, such as from CIMIS. For deciduous trees, this is often not of concern, because in the winter they don't have leaves and therefore are not transpiring anyway. For evergreen subtropicals like citrus and avocado, this could be an important source of water.
In many situations in the Central Valley and along the coast there can be periods where fog can represent a significant proportion of the water requirement for an orchard. These periods would be for winter tule fog in the Valley and along the coast in the spring and early summer. A recent publication by Rick Snyder at UC Davis has just been released that shows how this fog water can be incorporated into an irrigation schedule. You can see it at the UC's California Institute for Water Resources website: http://anrcatalog.ucanr.edu/pdf/8532.pdf, http://ciwr.ucanr.edu/california_drought_expertise/droughttips/
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