By Sara S. Moore
The fog comes/ on little cat feet, wrote Carl Sandburg. We here in the San Francisco Bay Area follow it on Twitter under the name Karl the Fog. It seems like a sentient being that winters on the water and summers on the land. It contributes a gentle touch to the atmosphere, keeping coastal plants and animals living within their narrow comfort zone. It is the natural air conditioning for coast-siders. It is the preferred summer water source for Sequoia sempervirens—coast redwood—the world’s tallest tree (Limm et al. 2009). Throughout history fog has also been tapped to generate drinking water, such as the harvesting of fog-drip from trees using cisterns in the Canary Islands.
There are also many varied modern efforts at tapping fog water for human use. One example with mixed results began in 1985 in Canada. An atmospheric physicist at Environment Canada named Dr. Robert Schemenauer was approached by an international aid agency with this question: can fog be used for water supply in the desert in Chile? His “proof of technology” project resulted in the world's first large operational fog collection project being built at El Tofo, Chile. It served the nearby coastal community of Chungungo from 1992 until 2003. The project delivered 15,000 liters of fog water per day on average, some days delivering over 100,000 liters. The size of the community doubled as a result. After 10 years of successful water production, the community leaders abandoned the fog collectors, eventually building their own desalination plant. The caretaker for their 100 large fog collectors was let go, and the collectors decayed. In an article about this shift away from fog collection, a representative of the aid agency that began this project, the International Development Research Centre, reflected: “people have certain visions of what it means to be developed, and one of them is that water should be brought to you by the state, and you should never have to think about it.”
Although the Chungungo project did not continue, Dr. Schemenauer, one of the founders of modern fog collection, persists in his work helping establish fog-water systems for isolated high-country communities in the developing world through FogQuest, the NGO he co-founded in 2000. He makes community engagement a priority in his projects.
FogQuest’s 1 m2 “standard fog catcher” uses a special polyethylene mesh (called Raschel mesh) that is both effective at capturing fog droplets and is wind-resistant. One of the longest-running (since 2006) and successful FogQuest collection arrays is located in Tojquia, Guatemala, where 35 large (40 m2) collectors trap 7,000 liters (1,849 gallons) of water a day during the winter dry season (FogQuest 2017). Dr. Schemenauer points to that project as having a “bright future” in part because of its robust maintenance regime. Other current projects include other sites in the highlands of Chile (the Atacama Desert Center and Falda Verde), Ethiopia, Nepal, Eritrea, and Morocco (read a 2016 update about this project: Fog harvesting brings water to Morocco’s rural communities, which combines FogQuest collectors and a newer German design created for high wind environments).
Fog collection pilot projects have also been undertaken by many other institutions around the world, including through the University of South Africa. The South African collectors were adapted for local weather conditions: “instead of having one flat vertical panel, we now put three panels (30 m2 each) in the form of a triangle […] provid[ing] stability to the system during storms,” per a 2013 report.
What is fog and how will climate change affect it?
For most purposes, fog is a cloud that touches the ground. There are different types of fog. One way some types form when warm, moist air passes over a cool surface, causing water vapor to condense on tiny particles (called condensation nuclei). But historically the presence of fog has been measured at airports with regards to navigation (officially, “fog” is present when visibility is less than 1 km), so fog scientists trying to understand how climate change and other factors are affecting fog in, for example, coast redwood habitat have to interpolate trends from airport data which aren’t tailored to their purposes. Fog also doesn’t collect as water in uniform ways: wind and the composition of droplets change how it gathers on collectors. The science of determining the optimal places for fog collection and the optimal collector construction is still being developed through modeling and trial and error.
The question of how climate change is affecting fog is highly unresolved, and probably will be for some time. Some researchers speculate it is declining (see the Johnstone and Dawson 2010 study that shows a 33% decline in summertime fog hours off the coast of California), some that it is intensifying. In any case, the atmospheric, oceanic, and terrestrial systems that produce fog are highly variable and undergoing changes: their future interactions can’t be projected with much certainty.
Ideal conditions for a bumper crop of fog
For the best water production, fog collectors should be constructed perpendicular to the prevailing wind. Drops will form on the mesh and then fall into a trough that is angled to fill a tank. On average, a fog collector of the sort built by FogQuest will produce 3-15 liters (about 1-4 gallons) per day per m2. If the fog event is especially productive, the collector may yield 50 liters (about 13 gallons) per m2 in one day (source).
You can’t get these results by hoisting up a fog collector in any back yard. Fog collectors are most productive in high mountains very close to the ocean. One report from South Africa specifies the following requirements for a viable fog collection project in local conditions:
- It must be in an area where fog events are frequent year-round and last several hours.
- It must be at least 1,000 m above sea level and receive at least 90 days of fog precipitation per year.
- The water content of the fog must be high.
- There must be wind with the fog to ensure a minimum volume of air blown through collectors.
The fog collector mesh has a 10 year life span. For a large collector of 40m2 the cost of the standard fog collector mesh and the poles and cables that comprise the frame is between $1,000-1,500 USD. The structure on which it is suspended is flexible in wind storms and earthquakes, so it is relatively easy to put back into place after a natural disturbance. There is no permanent infrastructure required (e.g., no concrete slabs necessary, no electrical cables for pumps): maintenance is relatively cheap, consisting of replacing worn out mesh or damaged pipes, cables, troughs, or water containers. Although it is relatively cheap, a commitment must be made to maintenance, as Chungungo exemplified.
To get ahead of that obstacle, Dr. Schemenauer recommends prioritizing connecting the local people to the project: “The success of projects depends on having people in the community involved right from the beginning, before you put a fog collector up.”
Dr. Schemenauer emphasizes the importance of involving women and children—the whole community, showing them the concept and starting with a test structure (a 1x1m Standard Fog Collector, for example) as a demonstration. If materials are scarce, a simple mosquito net can work for a proof-of-concept demonstration. The initial construction of fog collectors is relatively easy compared to long-term maintenance, so the sustainability of a fog collector project hinges on local buy-in.
Your new California coastal utility: CalFog?
As romantic as it would be, fog is not likely to ever be a viable source of new water for human consumption in cities, especially not in the developed world with its high-demand user habits. Ultimately fog water requires too much effort and expense for the quantity of water needed. The lifestyle of urban water users would have to change and the cost of fresh water from inland sources would have to skyrocket (and/or quality would have to plummet) to make a utility-scale fog collection project make sense for a city.
In isolated coastal areas where the two main alternative water sources are fog collection and desalination (as in Chungungo), the people who run the desalination plants are unlikely to be equipped to operate a hybrid system integrating both sources: it will be one or the other. If commitment to local maintenance is already a problem, the relative unreliability of fog water compared to desalination might be a deciding factor. Also, if a community has never tried fog harvesting, it will face the problem of any new public infrastructure project (e.g., the questions associated with building water storage basins, how to support collection and maintenance, etc.).
The optimal place for fog water collection for human water needs is a high mountain/ coastal community with a small, isolated population with low water demand, as in the examples above.
The next most cost-effective use might be for agriculture such is in Falda Verde near Chañaral, Chile, where fog water supports a commercial aloe vera plantation through drip irrigation (Carter et al. 2007). The project there is aiming at integrating a fog-fed fish farm, the water from which would add fertilizer to the plantation (aquaponics), according to Dr. Daniel Fernandez, who visited the site in March 2017. Majada Blanca, Chile, has an experimental olive farm fed exclusively with fog water (with a goal of selling fog-fed olive oil to advertise the technique). Its first harvest took place in May 2017.
FogQuest volunteer Chris Fogliatti suggested another drip irrigation system might take the form of fog-collecting mesh installed around an individual native tree sapling. He suggests this might be a useful approach to watering landscaping at high altitudes along the coast; fog water could also be used to feed hydroponic operations producing California’s newly legalized cash crop, marijuana.
Is it safe to drink fog water?
Fog water tends to be of high quality, although it should be subjected to regular testing and filtration if it is being consumed by humans.
There is a concern about bioaccumulation of mercury in coastal animals due to fog exposure. According to Peter Weiss-Penzias at UC Santa Cruz, it appears that mercury levels, on average, are ten times higher in coastal mountain lion whiskers than those found inland. The fog these animals live in can be 20 times more polluted with mercury than rain. This is not a concern for humans, since the amounts are too small to affect humans and we don’t consume anything that consumes fog, but it might be a concern for the long-term health of animals in coastal habitats.
The future of fog
Johnstone and Dawson’s 2010 study illustrating a decline in California’s coastal fog has been widely discussed and questioned. Meanwhile, over the past ten years Dr. Daniel Fernandez says coastal fog in Chile has been in decline, with a more pronounced drop than what has been observed in California, but the long-term trends aren’t clear. It might be connected to the Pacific Decadal Oscillation, or a regional effect. Presuming the fog stays with us, our understanding of how best to utilize it as a natural resource will continue to expand, thanks to the many thoughtful people who keep their heads in the clouds.
Many thanks to those who contributed to this research for this article: Dr. Daniel Fernandez (Cal State Monterey Bay), Bill Fox (Center for Art and Environment, Nevada Museum of Art), Dr. Robert Schemenauer (FogQuest), and Chris Fogliatti (FogQuest).
FogQuest – the modern pioneer in fog collection for water supply in isolated communities in the developing world, an all-volunteer NGO where 90% of funds received from donors and foundations is spent directly on fog-water projects.
The CloudFisher by Aqualonis – a newer design of fog collector designed for high winds. It is more expensive at the outset but intended to be cheaper to maintain than the Raschel mesh fog collectors. Its comparative efficiency in producing water is still being tested. A study in 2014-2015 (Mount Boutmezguida, Morocco) showed the CloudFisher mesh to be more productive (see results table on p. 20-21).
Warka Water – a project by designer Arturo Vittori (see the most recent updates on Facebook). This fog collector, still in the pilot stage, is cylindrical, designed to resemble a tree (the warka fig tree), and made at least in part using locally sourced natural materials (bamboo, hemp, and bio-plastic). It is being piloted in Italy, with the target destination of villages in the NE Ethiopian high plateau. The current model (3.7) includes photovoltaic illumination.
Device pulls water from dry air, powered only by the sun (April 2017) – Scientists at the Massachusetts Institute of Technology and UC Berkeley have built a device that can “pull liters of water out of the air each day in conditions as low as 20 percent humidity.”
The California fog collection story in a 25-minute video by Al-Jazeera’s “TechKnow” (April 2017), featuring an interview with fog scientist Dr. Daniel Fernandez, California State University Monterey Bay.
Want to Make Your Own Fog Collector?
Bayside Fog Collectors will be the small-purchaser distributor for the company that produces Raschel mesh– Marienberg– starting in late 2017, along with other products for people who want to make their own or buy a custom-built backyard fog collector.
Get the 2017 FogQuest Fog Water Collection Manual ($35 Canadian).
Fog Research Resources
The International Fog and Dew Association – founded at the 7th International Conference on Fog, Fog Collection and Dew held in Poland in 2016. The next conference is expected to be in Taiwan in 2019 and in the U.S. in 2022.
Fog Research: Network and Sites – a new fog StoryMap designed to be a repository for photographs and data from an international network of fog researchers, managed by USGS fog scientist Dr. Alicia Torregrosa, currently featuring research projects in the U.S. (California), Namibia, and Chile. Dr. Torregrosa is also the convener of a weekly webinar series for fog researchers, hosted by the Coastal Fog Online Group, part of the Pacific Coastal Fog Project.
The Summen Project – a $1.75 million, three-year study underway on the U.S. West Coast to study the relationships between fog, climate change, redwoods, and human activities. Read about the project’s launch: Researchers Eye Foggy Link Between Redwoods, Climate Change (2016).
About the Author
Sara S. Moore is a climate change adaptation researcher based in Oakland, California. She worked on the Sonoma County Adaptation Strategy (2015) as part of its Climate Action 2020 plan. She wrote a white paper on the Marin case study in scenario planning for the California Climate Vulnerability Assessment (Moore, Zavaleta, Shaw, 2012) and a guidance on implementing scenario planning for natural resource managers for the California Coastal Conservancy and Point Blue Conservation Science (Moore, Seavy, Gerhart, 2013). She holds a Master of Public Policy degree and an MA in International and Area Studies from UC Berkeley.