Climate and Wildfire Link Becoming More Complex in the Southwest

The Dragon Bravo Fire that burned across the Grand Canyon’s North Rim and destroyed the Grand Canyon Lodge is one of many recent wildfires with devastating impact in the Southwest. Wildfires are growing larger and more intense across the region. High temperatures, prolonged droughts, and increasing aridity—or drying of the region—are well-known factors driving the rise in these destructive fires. New research by members of the CLIMAS team exposes a more complex and nuanced relationship between climate and wildfire in the Southwest.

One critical factor in the relationship between wildfire and climate is the diversity of ecosystems across the region. The Southwest includes arid deserts with iconic saguaros, shrublands with creosote and mesquite, grasslands, and conifer forests in the higher elevation mountains. Climate plays a different role in wildfire activity across these different ecosystems. In our study we analyzed climate conditions that contributed to years of extreme wildfires across three vegetation zones: conifer forests, shrublands, and grasslands.

Conifer fires, such as those in the Arizona and New Mexico mountains, account for 49% of wildfires. Over the study period (1984-2021), we showed that conifer fires have consistently increased in total area burned, number of fires, and average fire size. Years of extreme wildfire in conifer forests (such as 2002, 2011, 2012) often followed prolonged droughts and periods of significant aridity, often linked to La Niña conditions.

Shrublands, which include woody perennial plants like creosote, sagebrush, and mesquite, extend across parts of the Mojave and Sonoran Deserts into the lower flanks of mountains across Arizona and New Mexico. We found that shrubland wildfires made up 33% of the area burned during the study period. While the number of shrubland fires has remained steady, the average size and total area burned have increased. Our analysis showed that climate conditions for extreme shrubland fire years included a wet preceding fall and winter that allowed for growth of fine fuels right up to the spring fire season.

In grasslands across the region, the widespread presence of invasive grasses such as red brome and buffelgrass is changing fire regimes in these systems. These non-native species respond quickly to precipitation, grow rapidly, and are fire-adapted, often spreading further after a burn. Invasive grasses are providing fuel for wildfires in areas that historically have not experienced large wildfires. The Bighorn Fire in Arizona (2020), which started in low-elevation desert shrubland and burned into higher elevations, exemplifies this growing risk.

We found that grassland wildfires primarily occurred in Eastern New Mexico, and the size and frequency of these fires remained consistent. Like shrublands, years of extreme grassland fires were tied to preceding wet periods that stimulated grass growth, followed by warm and dry conditions. 

The relationship between climate and wildfire in the Southwest is becoming more complex. Drought and high temperatures can provide conditions for increased wildfires in conifer forests, while rain and wet conditions can promote fuel growth for wildfires in shrubland and grasslands. Understanding the nuances of the relationship between climate and wildfire in the Southwest is crucial for planning fire mitigation strategies that are tailored to local conditions.