Study Links Low Eurasian Snowfall to Increased California Winter Wildfires

California’s wildfire season has historically peaked in summer and tapered off by winter, when cooler, wetter weather typically reduces fire risks. However, January 2025 defied this pattern, as Southern California experienced some of the deadliest and costliest wildfires in state history.

A new study published in Nature Communications suggests that these unusual winter wildfires may be linked to low autumn snow levels in western Eurasia. Researchers propose that tracking snowfall in Eurasia could help forecast winters in California with higher wildfire risks.

Investigating Climate Drivers of Winter Wildfires

The research team, led by Shineng Hu, a climate scientist at Duke University, initially explored potential connections between winter wildfires and ocean temperatures, including La Niña events, which are associated with drier-than-average conditions in California. They also examined the influence of sea ice variability on global weather patterns. However, these factors showed only weak correlations with California’s winter wildfires.

Compared to oceans and sea ice, the impact of snow cover on global weather patterns remains understudied, Hu noted. However, a previous study by a colleague in his lab highlighted the connection between snow cover and weather patterns, prompting the team to investigate further.

Discovering the Eurasian Snowfall Link

The researchers found a significant correlation between low snow cover in western Eurasia and increased winter wildfires in California. Hu described his initial skepticism:

“When I saw the result, I was suspicious, because we all know that correlation doesn’t mean causality.”

To validate their findings, the team ran hundreds of climate model simulations, reducing snow cover in Eurasia. The simulations consistently showed an increased probability of winter wildfires in California.

“At that point, we were pretty much convinced that there could be something interesting happening over there,” Hu said.

How Low Snow Cover Triggers Wildfires

The study explains that low snow cover in Eurasia allows the land to absorb more solar energy, disrupting the atmosphere above it. This disturbance generates large atmospheric waves called Rossby waves, which travel eastward along the jet stream across the Pacific Ocean. These waves contribute to the formation of a high-pressure zone over California, creating hot, dry, and windy conditions that are highly conducive to wildfires.

Judah Cohen, a climatologist at the Massachusetts Institute of Technology who was not involved in the study, emphasized the significance of this mechanism:

“I’m glad to see this group saying snow can do something similar to what ocean temperature anomalies can do. I’ve been surprised by how important this mechanism is for U.S. weather in the winter and how little there is about it in the literature.”

Cohen added that the study highlights a previously overlooked gap in climate research:

“This is just one missing gap that people didn’t even realize. We want to add that.”