Wildfire smoke reached almost every lake in North America in 2019-2021

Wildfire smoke, sometimes drifting from hundreds of miles away, touched nearly every lake in North America for at least one day per year from 2019 to 2021, according to a new study.

Even more significantly, 89% of the lakes in North America experienced smoke for more than 30 days during each of those three years of intense wildfire activity.

“That was surprising, even to us,” says Mary Jade Farruggia, a PhD candidate in the Graduate Group in ecology and the environmental science and policy department at the University of California, Davis.

“With this study, we quantified for the first time the scope of the smoke problem. We show that it’s not just a widespread problem, but one that is long-lasting in a lot of places.”

Lake-smoke days

The study introduces a concept the authors call the “lake-smoke day” to serve as a metric for monitoring smoke prevalence at lakes. It refers to the number of days a lake is exposed to smoke in any given fire season.

A lake-smoke day metric could help establish a baseline to better understand the extent and intensity of events such as 2023’s persistent blanket of wildfire smoke from Canada that reached the Northeastern United States and crossed the Atlantic Ocean to Western Europe.

The authors established the metric using a hazard-mapping product from the National Oceanic and Atmospheric Association that quantifies smoke density based on a combination of satellite imagery and ground-based measurements. They also analyzed databases of about 1.3 million North American lakes larger than 25 acres to learn the prevalence and duration of exposure.

“Smoke is widespread, and smoke is pervasive,” says Steven Sadro, a limnologist and associate professor in the environmental science and policy department and senior author of the study published in the journal Global Change Biology. “We knew that by looking out the window and looking at satellite images we see almost every summer. Now we’re starting to quantify it.”

Smoke science

While wildfire has been a consistent and even healthy presence on the landscape for millions of years, the frequency and severity of catastrophic wildfires in recent years is novel compared to previous decades. For that reason, the impacts of smoke on natural systems are understudied.

This study is part of a growing, broader effort to examine how smoke affects lake environments. The authors worked with the Global Lakes Ecological Observatory Network, or GLEON, to create a working group to share, understand, and communicate these impacts.

They reviewed the known and theoretical impacts of smoke on lakes, such as how smoke can change the amount and composition of solar radiation that reaches lakes. Smoke and ash also can alter the deposition of carbon, nutrients, or toxic compounds. Yet these impacts tend to be lake-specific and highly variable.

“We just don’t know yet how smoke affects food webs, lake ecology, or what the future of these systems will be if there’s an increase in lake-smoke days,” says Farruggia. “I think quantifying the scope of the problem is really the first step. We’re pointing out that this is something we need to manage for across the globe, and not just areas affected by wildfire.”

The research was funded primarily through the National Science Foundation.

Source: UC Davis

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