Rain falling through wildfire smoke can deliver unusually large bursts of nitrogen, phosphorus, and potassium to ecosystems, potentially serving as an increasingly significant ecological consequence of fire, according to a study published Aug. 25, 2026.
Nutrient Delivery Through Wet Deposition
The research, published in the journal Global Change Biology, was led by scientists from the University of Utah, Utah State University, and the Cary Institute of Ecosystem Studies. The study represents the first large-scale analysis to examine how wildfire smoke particles are delivered to ecosystems through rainfall across hundreds of U.S. sites over multiple years.
The Connection Between Smoke and Rain
When rain falls through smoke, it washes particles to the ground in a process known as wet deposition. Once these nutrients are dissolved in water, they become bioavailable, meaning organisms in lakes or on land can immediately access them.
"You can see the remnants of material that are left behind when the water evaporates," said Alexandra Ponette-González, an urban ecologist at the University of Utah and the Natural History Museum of Utah. "When rain hits an ecosystem, the nutrients are bioavailable—organisms, whether in lake or on land, can immediately access them because they're dissolved in water."
Increasing Frequency of Events
The study analyzed 250 sites across 16 climate regions during 2014, 2020, and 2022. Researchers found that smoke-rain events are becoming more frequent. In 2014, monitoring sites averaged about four days per year where smoke and rain coincided. By 2020, that average rose to six days, and by 2022, the average increased to approximately 22 days per year.
In a high-smoke year like 2022, smoke-rain days accounted for only about 5% of days but delivered between 20% and 30% of the annual rain-deposited nitrogen, phosphorus, and potassium.
Shifting Regional Hotspots
The geographical hotspots for these events shifted over the study period. While the Upper Midwest was the top hotspot across all three years, other regions saw peaks at different times: the Northern Rockies in 2014, the Southwest in 2020, and the Ohio Valley in 2022.
"Smoke plumes are a large source of gases and particles in the atmosphere," said Heather Holmes, a chemical engineer at the University of Utah. "Understanding the complex interactions between smoke, atmospheric dynamics and precipitation is critical to gain insight on nutrient transport and deposition."
Ecological Impacts and Nuance
While the study identifies these nutrient pulses, the authors emphasized that the findings do not necessarily mean wildfire smoke "fertilizes" ecosystems in a way that benefits growth or productivity. The ecological impact depends on the specific characteristics of the receiving ecosystem.
In nutrient-poor mountain areas, an added pulse of nitrogen or phosphorus may have different consequences than in areas already receiving abundant nutrients from agriculture. In lakes, additional nutrients can increase production and shift community composition, while in forests, smoke deposition can have both positive and negative effects, such as stimulating tree growth while potentially decreasing survival.
Research Methodology
The research utilized satellite-derived smoke observations and national network rainfall data, including data from the National Atmospheric Deposition Program, which has monitored rainwater chemical composition since the 1970s to track acid rain.
"The impact of wildfire on rain chemistry has been largely overlooked," noted coauthor Kathleen Weathers, an ecosystem scientist at the Cary Institute.
The Importance of Atmospheric Fallout
"It's important to remember that what goes up must come down," Ponette-González said, noting that while much focus is placed on how smoke affects human health, the environmental impact of what falls out of the atmosphere remains a critical area of study.
