Fog drip explained

Fog drip is water dripping to the ground during fog. It occurs when water droplets from the fog adhere to the needles or leaves of trees or other objects, coalesce into larger drops and then drop to the ground.^[1]

Fog drip can be an important source of moisture in areas of low rainfall, or in areas that are seasonally dry.

Studies in the United States

• On the leeward slopes of Maui, the original dryland cloud forests were destroyed during the 19th century but historically were inhabited by native Hawaiians, so there must have been water sources. Isotopic (Oxygen-18) analyses of one of the few remaining areas of native forest, at 4000feet elevation in the fog belt, found that fog drip was a major component of stream flow and shallow ground water at higher altitudes in the watershed.^[2]
• On arid Santa Cruz Island, a study of the southernmost Bishop pine (Pinus muricata) forest in California found that summer cloud shading and fog drip mitigate the effects of summer drought. Even though fog cover in summer only occurs 15% of the day, this minor amount of fog enabled trees and soil microbes to grow at an increased rate. However, winter rainfall was the primary driver of summer tree growth, which is only aided by reduced soil evaporation in summer due to fog drip. Cloud cover and fog drip have enabled this relict pine forest to persist from prehistoric times when the climate was wetter.^[3]
• In the Bull Run River, Oregon, fog drip from mature Douglas fir (Pseudotsuga menziesii) forest adds 35inches of moisture per year, a 41% increase over that from rain and snow, and importantly, of all moisture in the dry May to September season.^[4]
• In California Coast Ranges, a single Coast redwood (Sequoia sempervirens) can "douse the ground beneath it with the equivalent of a drenching rainstorm and the drops off redwoods can provide as much as half the moisture coming into a forest over a year".^[5] Dawson reported that in a study of northern California redwood forests, 34% of annual hydrologic input was from fog drip. In areas where trees had been cut down, the average annual input from fog was only 17%, proving that the redwoods were required for the fog moisture input to the ecosystem.^[6] In an Occidental, California study beneath a single 200adj=midNaNadj=mid Douglas fir on a ridge dividing the moister western slope of the California Coast Range from the drier eastern slope, moisture collected under the tree averaged 58inches versus 27inches in an adjacent open meadow.^[7] On Inverness Ridge in Point Reyes National Seashore fog drip from Douglas firs in summer may add 20inches to the otherwise 40inches of annual average rainfall.^[8] Further south, on Cahill Ridge on the San Francisco Peninsula (between Pilarcitos Creek and Crystal Springs Reservoir) at an altitude of 1000feet, Oberlander measured fog drip beneath Tanoak (Lithocarpus densiflorus), Coast redwood and three Douglas fir trees, the latter 125feet tall. He found that the trees most exposed produced the most moisture and in five weeks of measurement (July 20–August 28, 1951) fog drip below the tanoak produced 59inches of moisture, more than the total annual precipitation on nearby grasslands and chaparral. The Douglas fir produced 7inches-17inchesin (-in) of fog drip and appeared to provide unique conditions supporting the orchids Giant helleborine (Epipactis gigantea) and Phantom orchid (Cephalanthera austiniae), since these plants were found exclusively in these moist ridge tops.^[9]
• In the Green Mountains of northern Vermont at elevations above 2500feet in the spruce–fir zone on the western slope of Camel's Hump, fog drip increased the total moisture available up to 67% over rainfall alone. The authors concluded that the needlelike leaves and twiggy character of the conifers in the spruce–fir zone serve as effective mechanical collectors of the wind-driven cloud droplets.^[10]

Outside the United States

• One of the few areas in the world where people climb to the hilltops to get water in times of drought is the Downs in England, where fog blows in from the English Channel to form what locals call "dew ponds", although they are formed by fog drip instead of dew.^[11]
• Near the Pacific coast of Peru and northern Chile, in the nearly complete absence of any annual rainfall, fog drip allows vegetation, including trees, to grow in small areas called "Lomas," which contrast with the surrounding areas of barren desert.^[12]
• In the arid climate of northern Kenya, fog drip may be an important source of infiltration and groundwater recharge, where isotopic analysis found the latter to be a mixture of rainwater and fog drip.^[13]
• In the Pacific Ocean off Mexico, Cedros and Guadalupe Islands support Monterey pine forests. Very sparse rainfall augmented by fog drip permits the existence of the forests.^[14]

See also

• Fog desert
• Cloud forest
• Dew

External links

• FogQuest is a non-profit Canadian charity dedicated to helping developing countries harvest atmospheric water
• Video: "Fog and Wind" - Cloud Forests of Santa Rosa Island, USGS Western Ecology Research Center

Notes and References

1. Web site: Fog drip - AMS Glossary . . December 15, 2014.
2. The influence of microclimates and fog on stable isotope signatures used in interpretation of regional hydrology: East Maui, Hawaii . Martha A. . Scholl . Stephen B. Gingerich . Gordon W. Tribble . Journal of Hydrology . July 2002 . 264 . 170–184 . October 16, 2010 . 1–4 . 10.1016/S0022-1694(02)00073-2 . 2002JHyd..264..170S.
3. Cloud shading and fog drip influence the metabolism of a coastal pine ecosystem . Mariah S. Carbone . Global Change Biology . 2012 . 19 . 2 . 484–497 . 10.1111/gcb.12054. 23504786 . etal. 2013GCBio..19..484C . 16511876 .
4. Fog Drip in the Bull Run Municipal Watershed, Oregon . R. Dennis Harr . October 1982 . Journal of the American Water Resources Association . 10.1111/j.1752-1688.1982.tb00073.x . 18 . 5 . 785–789. 1982JAWRA..18..785H .
5. News: Clues To Redwoods' Mighty Growth Emerge in Fog . Carol Kaesuk Yoon . New York Times . November 24, 1998 . October 16, 2010.
6. Fog in the California redwood forest: ecosystem inputs and use by plants . T. E. Dawson . Oecologia . September 1998 . 10.1007/s004420050683 . 28307672 . 117 . 4 . 476–485. 1998Oecol.117..476D . 26820268 .
7. Web site: Capturing the Clouds: Fog Drip & Cisterns . Robert W. Kourik . 1995 . October 16, 2010.
8. In the Fog Drip at Point Reyes . Bay Nature . Jules Evens . August 12, 2012 . April 8, 2013.
9. Summer Fog Precipitation on the San Francisco Peninsula . G. T. Oberlander . Ecology . October 1956 . 1933081 . 37 . 4 . 851–852 . 10.2307/1933081.
10. Precipitation from Fog Moisture in the Green Mountains of Vermont . Ecology . November 1968 . 1205–1207 . 1934518 . H. W. Vogelmann . Thomas Siccama . Dwight Leedy . Dwight C. Ovitt . 49 . 6 . 10.2307/1934518.
11. Fog Drip May Hold Key to Drought Relief . Calvin Frazer . Popular Mechanics and Inventions . June 1931 . October 16, 2010.
12. Monitoring fog-vegetation communities at a fog site in Alto Patache, South of Iquique, Northern Chile, during 'El NiZo' and 'La NiZa' events (1997–2000) . 2001 . In Second International Conference on Fog and Fog Collection . Schemenauer R.S. . Puxbaum H. . 293–296 . October 17, 2010 . Pinto R. . Larrain H. . Cereceda P. . Lazaro P. . Osses P. . Schemenauer R.S. . September 27, 2011 . https://web.archive.org/web/20110927160612/http://www.uc.cl/geografia/cda/pdf/est_patache/id_cda_23.pdf . dead .
13. Fog Drip as a Source of Groundwater Recharge in Northern Kenya . Water Resources Research . 1406–1410 . August 1988 . October 16, 2010 . Neil L. Ingraham . Robert A. Matthews . 10.1029/wr024i008p01406 . 1988WRR....24.1406I . 24. 8 .
14. Oberbauer, Thomas A. (2013), "Floristic Analysis of Vegetation Communities on Isla de Cedros, Baja California, Mexico," https://www.academia.edu/1109025/Floristic_analysis_of_vegetation_communities_on_Isla_de_Cedros_Baja_California_Mexico, accessed 20 Jun 2018