Poor tourists. They read about sunny California and come for their summer vacation traveling the scenic Highway 1 only to find days of fog. Fall and late spring often have much less fog than in the height of summer.
I just returned from two wonderful days on the coast 100 miles north of San Francisco. I got lucky with glorious fog-free weather. What visitors and locals fail to notice along the coastal Highway 1 is the extra 32 to 123 inches of "rain" each year. Although actual summer rain is scarce-to-nonexistent in the Northern California Mediterranean coastal zone where I live, another type of "rain," consisting of droplets of condensed fog, is a frequent occurrence. Moist summer fog condenses on the leaves of plants, mostly tall trees.
Shortly after moving to my mountain ridge, I noticed that a foggy summer evening produced the sound of steady rain beneath the tallest trees, while the meadow 20 feet away remained dry. I became obsessed with fog drip.
I put a rain gauge beneath a 125-foot tall Douglas fir tree near my garden and another 100 feet away in open grasses. The needles of the Douglas fir have an immense surface area for condensation. The Douglas fir tree averaged up to 2-1/2 times more "rain" year-round than the open field a mere 100 feet away. I discovered over 10 years of records that this single tree can gather one or more inches of water during a single heavy fog—six inches during one very foggy August! That rare six-inch fog drip equaled 163,000 gallons of water for every acre of tree foliage! It is fog drip that helps water the edges of redwood grove just around the corner from my house and allows the redwoods to expand their growth into the adjacent fields, shrubs, and smaller trees. (The trees at the edges of the forest get much more of the fog drip than those inside the grove. The perimeter trees strip most of the fog moisture from the sky.)
Fog drip is so uncommon that it is rarely found even two miles inland from my garden. I learned that microclimates can indeed be very small, special places. A microclimate that never shows up on the evening weather report. Nature sure has extraordinary niches as part of its fabric of life.
Alas, coastal-bound tourists are not impressed at all with fog drip. It rains on their parade— especially if camping in a tent beneath coastal redwoods.
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