Western US is fending off more fires before they start—and still getting hit by its biggest blazes yet

The annual occurrence of wildfires in the Western United States has decreased by approximately 28% over the last thirty years, despite a significant increase in the total area burned and the resulting damages. A study indicates that more than 40% of this decline can be attributed to a reduction in fires ignited accidentally by humans.

The relationship between human population density and wildfire frequency is complex. In regions with low population densities, the number of fires tends to rise with increasing population. However, beyond a specific density threshold, the frequency of fires diminishes. Understanding the impact of changing human demographics on wildfire patterns is crucial for scientists as they work to forecast future fire activity more accurately.

According to Gavin Madakumbura, an atmospheric and oceanic scientist at the University of California, Los Angeles and the lead author of the study, "It would be premature to talk about informing fire management based on these results, but the main implication is that we can incorporate these results into projections of future fire activity."

The findings are published in the journal Earth's Future.

More burning, fewer blazes

The consequences of wildfires are escalating in many parts of the Western U.S. From 1992 to 2020, the area burned annually increased by nearly 4% each year, with 2020 witnessing nine million acres of land engulfed in flames—an area larger than the entire state of Maryland.

Despite widespread assumptions that the frequency of fires is on the rise, a comprehensive analysis conducted by Madakumbura and his colleagues revealed a decline in fire incidents from over 25,000 annually in 1992 to around 18,000 in 2020. This translates to approximately 305 fewer fires each year across the 11 continental western states.

Madakumbura attributes the increase in burned area primarily to climate change driven by human activities, which exacerbates hot and dry conditions conducive to larger fires. However, the initiation of fires is influenced by various factors beyond climate, including human behavior and fire prevention strategies.

"We often hear that the burned area, fire damages, and fire frequency are increasing. However, fire frequency is a more complex issue," Madakumbura stated. "We aimed to investigate this with the best tools available to determine whether fire frequency is indeed increasing."

In many western regions, fires ignited by humans have declined more sharply than those caused by natural phenomena such as lightning. However, the trends differ by region: for example, significant declines in human ignitions were observed in California and Arizona, while Wyoming saw an increase.

To explore this discrepancy, the research team analyzed population density data and financial statistics from the U.S. Census Bureau detailing expenditures on fire protection and management at the state level.

They discovered that states with higher population densities tend to allocate significantly larger budgets for fire protection. California, for instance, spends over seven billion dollars annually more on fire management than Wyoming.

These findings align with the concept of "pyric transition," which posits that in sparsely populated regions, an increase in population leads to more human-caused fires. However, beyond a certain population density, a larger population also results in enhanced fire prevention measures and public awareness initiatives that can mitigate fire risks. This, combined with the fragmented landscapes of more densely populated areas, may contribute to a decrease in fire occurrence.

While a strong correlation exists between population density and fire prevention spending, the study's conclusions do not definitively establish that increased population density directly results in higher fire management budgets. As Madakumbura noted, fire prevention initiatives may also develop in response to escalating fire risks posed by climate change, which increases aridity in western regions.

In this context, climate change appears to trigger both an increase in fire frequency and, in well-resourced areas, proactive prevention measures to counteract that trend. Nonetheless, Madakumbura believes that population density significantly influences this relationship.

"We understand that higher human activity correlates with more accidental fire ignitions. Simultaneously, many regions invest heavily in fire prevention and awareness; thus, we should observe this trend in the data," he explained.

Madakumbura expressed satisfaction in uncovering the regional variations in fire frequency trends revealed by the study. "The data strongly indicate a possible causative relationship."

Not all good news

Certain exceptions persist: urban centers such as Los Angeles, Phoenix, and Denver are experiencing increased fire frequency despite their high population densities. Madakumbura suggested that this trend may be partly due to inconsistent reporting practices among regional fire agencies, where local jurisdictions document more instances of smaller, urban fires as populations grow, whereas state and federal agencies focus their efforts primarily on wildland fires.

Moreover, the "pyric transition" may not uniformly apply to individual cities or counties, although it seems pertinent at the state and multi-state levels.

The exploration of the links between human demographics and fire frequency will assist scientists in predicting future fire trends more precisely than if they solely considered climate change factors.

The study also highlights that the majority of fire damage to human communities originates from fires ignited by human actions. Additionally, intensive fire suppression tactics can lead to an accumulation of wildfire fuels, resulting in more severe fires when they do occur.