The frequency of catastrophic wildfires is increasing around the globe. Our ability to mitigate the risks associated with these fires, and the toll they take on communities, life, and the environment, will depend in large part on understanding their driving causes. But there remains significant debate over how interacting factors like climate change and fire suppression enable ignitions to grow into extreme wildfires. While regional syntheses attribute increases in wildfire activity to both rising global temperatures and fuel accumulation due to historical fire suppression, they have yet to separate the influence of these drivers at watershed or even finer scales. Understanding how these factors interact is crucial for determining when and where fuel reduction treatments will be most effective.

Researchers at Washington State University analysed how historical climate change and fire suppression are influencing wildfire activity at management-relevant scales, focusing on two mixed-conifer watersheds in Central Idaho: Johnson Creek, a 565-km2 sub-catchment of the South Fork Salmon River, and Trail Creek, a 167-km2 sub-catchment of the Big Wood River. Using a novel modelling technique, researchers simulated the frequency, magnitude, and risk of wildfires over a four-decade period (1980-2017) with and without historical climate change and fire suppression. They developed scenarios informed by historical climate data, including temperature and precipitation, current understanding of climate change trends, and fire suppression, modelled as complete fire exclusion. The modelling framework enabled them to examine how the drivers of wildfire are modified by local environmental conditions, including gradients in aridity and vegetation productivity.