The Pacific Ocean’s El Niño-Southern Oscillation (ENSO) is arguably the most influential climate driver on Earth. Its cycles of warm and cool waters in the central and eastern equatorial Pacific alter where ocean heat is released into the atmosphere, affecting atmospheric circulation, temperatures, and precipitation around the globe. 

A new study by CIRES and NOAA researchers shows how the state of ENSO in autumn, either the warm El Niño or cool La Niña phase, influences where wildfire activity will occur across specific regions of the United States during the following year. In particular, the analysis found a strong link between increased fire activity across the southern United States in the months following an autumn La Niña. 

“The El Niño-Southern Oscillation, through its La Niña and El Niño phases, offers a powerful tool for predicting the likelihood of extensive wildfire activity in several U.S. regions up to a year out, information that is crucial for wildfire managers as they prepare for wildfire activity,” said Andrew Hoell, a NOAA researcher and lead author of the new study published in the Journal of Geophysical Research: Atmospheres.

Hoell noted that the La Niña that emerged during autumn 2025 was followed by the historic western snow drought and an extraordinary early spring heat wave, which has led to drier, more flammable fuels.  

“Unfortunately, this year in the West and southern tier, it has been very dry and very warm,” Hoell said. “We’re talking about some historically warm conditions and at the same time below average precipitation. That sets up the land surface to be able to burn.”

Finding the link between ENSO and regional fire activity

During ENSO’s warm El Niño phase, the east-to-west Pacific trade winds weaken and a giant pool of warm surface water moves east, occupying the surface from the central Pacific to the coast of South America. During the cool La Niña phase, the Pacific trade winds strengthen, pushing warm surface water toward the western Pacific, cooling the eastern and central Pacific.

Changing the geographic region where these warm pools release heat into the atmosphere alters the jet stream—the high-altitude river of air that steers weather systems. This influence on atmospheric circulation controls regional precipitation and evaporative demand, key factors for fuel drying and fire potential.

In the new study, the researchers estimated the extent of large fires in nine U.S. geographic regions (shown in the map below) defined by the National Interagency Fire Center (NIFC). The NIFC, located in Boise, Idaho, is a place for employees of nine federal and state agencies to share resources and manage the logistics of fighting wildland fires. 

They estimated the extent of large fires in each region from satellite imagery and compiled data about precipitation and evaporative demand (how thirsty the atmosphere is) for overlapping three-month periods from 1984 to 2022 following El Niño and La Niña events. They also considered atmospheric pressure and sea surface temperatures to establish the physical links between ENSO and conditions in each geographic area. 

Examining how both the supply side of the hydrologic cycle (precipitation) and its demand side (evaporative demand) affect the extent of fires across the country is a new approach taken in the study. 

“It's uncovering findings that are both immediately useful to planners in the wildfire community, but also to encourage researchers to look more into this balance between supply and demand as they affect both fire and drought,” said Mike Hobbins, a CIRES researcher working in NOAA’s Physical Sciences Laboratory and co-author of the study. 

La Niña, drought, and fire 

The team’s results show that autumn La Niña events were associated with a greater than two-fold increase in the relative risk of extensive burns in the Southern, Southwest and Rocky Mountain regions in the following spring. Their analysis also found that the influence of La Niña lingered over the Great Basin and Northern California regions, increasing fire activity during the following summer.

By contrast, following an autumn El Niño, the likelihood of extensive burns was consistently halved in the Southern, Southwest, and Rocky Mountain during the following spring and summer due to higher precipitation and lower evaporative demand. At the same time, this large‐scale circulation promotes unusually high pressure over the northern tier, leading to an increased chance of large fires in the Eastern and Northern Rockies regions during the spring.

While the analysis provides a systematic diagnosis of how La Niña and El Niño influence the chances of extensive wildfire areas being burned across the contiguous U.S., the researchers caution that additional research on wind speed, fuel moisture, and vegetation, as well as improved predictability of evaporative demand, will be needed to improve the skill of localized fire risk models.