Wildfire smoke has covered up to 70 percent of California in recent years, affecting land and water: Study

Wildfire smoke covered as much as 70 percent of California in recent years — wreaking havoc not only on land, but also in the state’s vast freshwater ecosystems, a study published Wednesday has found. 

In the past 18 years, maximum smoke cover over the state has increased by about 116,000 square miles — equivalent to about 74.4 percent of California’s entire land area, according to the study published in Communications: Earth & Environment.

The authors came upon these dramatic percentages while researching how smoke has specifically affected the Golden State’s lakes. Although wildfire smoke regularly deposits aerosols and reduces sunlight in freshwater ecosystems, there is little data available about the overall impacts on these basins, the scientists noted.

Focusing on California’s three largest wildfire seasons on record — 2018, 2020 and 2021 — the researchers found that lakes endured an average of 33 days of high-density smoke between July and October.

“We’re looking at a scenario where for the next 100 years or longer, smoke will be a feature on the landscape,” senior author Steven Sadro, an associate professor in environmental science at the University of California, Davis said in a statement.

In two of the main study years, 2020 and 2021, medium- to high-density smoke surpassed 70 percent of the entire state in September and October, according to the study.

“What does that mean for fundamental ecology? What are the implications of those changes?” Sadro asked. “Those are the big questions we’re focused on in aquatic systems.”

To try to answer some of these questions, the scientists monitored sensors in 10 lakes across a wide range of coastal, mountain and inland environments as smoke settled during the three main study years.

They measured ecosystem health indicators, such as temperature, light and oxygen in the water, to determine how such characteristics change under smoky conditions, explained lead author Adrianne Smits, a UC Davis research scientist.

The authors hypothesized that smoke and ash would “dim the lights” and thereby affect rates of photosynthesis and respiration in aquatic life.

What they found was that while wildfire smoke does change light, water temperature and oxygen levels, it does so to a variable extent — depending on lake size, depth, smoke cover and nutrient levels.

Subsequent decreases in photosynthesis and respiration rates can then influence everything else, Smits noted.

“Food webs, algal growth, the ability to emit or sequester carbon — those are dependent on these rates,” she added. “They’re all related, and they’re all being changed by smoke.”

While the study focused on California’s lakes, the authors stressed that throughout North America, more than a million lakes were exposed to smoke for more than 30 days per year from 2019 to 2021. Those lakes, they continued, range from arctic to subtropical and face a variety of potential impacts from ongoing smoke coverage.

“We need to reframe how we’re thinking about wildfire smoke — as a seasonal weather phenomenon and not just an ‘event’ that happens and goes away,” Smits said. “We think about it for our health, but we should be thinking about it for ecosystem health, as well.”