What’s happening to Santa Cruz’s coastal fog?
If Santa Cruz seems less foggy lately, Dr. Daniel Fernandez, a professor at CUSMB, says it’s not a fluke, but part of a developing trend. Fernandez has been using fog collectors to measure condensation from fog for the past 11 years.
“At least at the sites where I have had measurements over the past few years, I would say I received less than 20 percent of the fog in each of the last two years,” says Fernandez, who now has more than 30 fog collectors set up as far south as Big Sur and as far north as Arcata, including two at Long Marine Labs in Santa Cruz.
While it’s tempting to celebrate the lack of fog—more sunny days!—the environmental importance of fog has become a growing area of research for local scientists, especially in the face of unprecedented climate change.
Fog offsets water stress in two ways, says Dr. Sara Baguskas, a postdoctoral environmental studies scholar at UCSC. One is by direct water input, which increases soil moisture through the deposit of water droplets onto surfaces and plant leaves. Fernandez estimates that direct water input ranges anywhere from none, if there’s no fog at ground level, to about a couple of litres in a day, depending on the location.
“Fog water input is not trivial,” says Baguskas. “The water inputs during the summer can almost amount to big rainfall events that we would experience in the winter, which actually sort of challenges our notion of Mediterranean climates. In foggy places, it can be functionally raining.”
The other way fog offsets water stress is through its “shading effect,” by reducing water loss to the atmosphere, which is like a sponge for moisture, especially on hot days.
The low-fog trend is most likely due to a “warm blob” in the ocean, which extends as far north as Alaska and south to Baja California, causing significantly above-average sea surface temperatures. Offshore, fog forms when warm air meets colder ocean. But if drought conditions are expected to be more frequent, and if sea surface temperatures continue to rise, we can expect that coastal fog will continue to decline.
“Plants here have evolved to survive seasonal water stress,” says Baguskas. “What’s different about the last four years is we have not received much rain, we are in the most severe drought of the past 1200 years, and so what we are seeing, in terms of an ecosystem perspective, are species of plants that are virtually tolerant to drought dying back.”
Why Fog Matters
Scientists are only now just beginning to quantify the impact of fog decrease on a long list of plant species that are succumbing to drought stress, including huge old trees like giant sequoias inland, coastal redwoods, and Monterey pines, which are numerous north of Santa Cruz, says Baguskas.
“The coastal forests depend on the fog, not only for the moisture but for the nitrogen,” says Dr. Peter Weiss-Penzias, an atmospheric chemist at UCSC who began studying what is actually in fog back in 2011.
“Studying fog, you get a whole new outlook on the foggy climate. I used to dread fog, now I hope for fog,” says Weiss-Penzias. “You really start to realize the volume of water that’s involved and the contribution that it makes to our landscape.”
Baguskas has spent the summer studying fog in the Salinas Valley. Low fog levels gave way to the important realization that “this is what California may look like in the future,” she says. “Understanding even the more subtle effects of fog may be really important in terms of climate change adaptation, and for people who manage water in agriculture,” she says.
Baguskas found that the shading effect of fog may be even more significant than its direct water input when it comes to agriculture.
“What I’m seeing is that there’s a significant reduction in water loss from strawberry fields on foggy days compared to sunny days,” says Baguskas. “This is not surprising, per se, but it’s the first time it’s been quantified. My goal is to integrate these observations into weather-based irrigation decisions.”
The foggiest August recorded over the past seven years was in 2011, with a total of 46 liters of fog water collected in Marina, says Fernandez. In August 2014, a mere 4 liters were collected at the same site, with 5 liters collected in August of 2015. And, one night in September of 2011, a fog collector in Big Sur caught 9 gallons, or 34 liters, of water, although Fernandez cautions that this was unusually extreme, partly due to the exposed, very windy site at a high elevation.
How Fog Works
Another active area of fog research includes finding out what, exactly, is in fog. “Fog is a medium that picks up things and moves them from one place to another. It’s a transport mechanism for chemical constituents,” says Baguskas.
It’s also a valuable source of naturally occurring nutrients. “The fog tends to be very heavy in ammonium and nitrate ions [the ingredients in fertilizer], and those definitely do fertilize the coastal area,” says Weiss-Penzias.
But it may also spread pollution. There is some research that suggests fog may transport pesticides from conventional farms to organic farms. And soon after Weiss-Penzias began analyzing fog for pollutants and other chemicals, he made a big discovery: unexpectedly high levels of mercury, to the tune of 100 times more concentrated than in rain.
“The hypothesis is that the fog sits over the ocean, and because of the ocean currents in our coastal area and how mercury gets altered in the deeper water by bacteria—it gets converted into methylmercury, which is a more toxic form and also more volatile—it can come out of the water as a gas and is quickly taken up by the fog droplets. It’s like a sponge, and whatever was coming out of the ocean was soaked up by the fog. Whereas in the rain, there is a distinct boundary layer,” says Weiss-Penzias.
The trace levels of mercury in the fog are well below any health dangers for animals and humans breathing the air. “It’s not like walking by a nuclear reactor,” says Weiss-Penzias. “But my big discovery was basically finding a new pathway for it to enter into the food web. Where you are on the food chain is going to determine how much mercury you get in your diet. The health threshold for human intake is .3 parts per million, and a lot of animals have accumulated up to that level, primarily fish because there’s a lot of methylated mercury in the ocean.”
Weiss-Penzias is expanding his research to study the amount of mercury that’s actually in plants and animals that live along the coast, “and we’re actually seeing an enhancement along the coast.”
Researchers invite readers to comment on their fog blog, fognet.ucsc.edu.
FOG BRAINS Dr. Sara Baguskas and Dr. Peter Weiss-Penzias of UCSC at Long Marine Lab in Santa Cruz, with a fog collector used to measure fog water. PHOTO: KEANA PARKER