Multifactorial interactions contribute to contrasting wildfire trends at mid–high latitudes of the Northern Hemisphere

Abstract

The contrasting changes in wildfires reflect their diverse responses to bioclimates, vegetation dynamics, and human activities. However, how wildfire drivers interact to shape contrasting wildfire dynamics remains unclear. Here, wildfire dynamics at mid–high latitudes (≥30°N) were analyzed using a burned area dataset from 1982 to 2018. We integrated structural equation modeling with fire regime triangle theory to define flammability, fuel, and human ignition as latent variables, thus explaining the major causes of contrasting wildfire trends. Wildfires increased in 2.91 % of land areas and decreased in 8.30 % at mid–high latitudes, exhibiting contrasting trends within and across ecoregions, in which flammability, fuel, and human ignition had impacts on wildfires with ratios of 0.63, 0.56, and 0.50, respectively. Temperature-driven flammability variations led to increasing trends in wildfires in fuel-rich forests, while increasing flammability, combined with reduced fuels from water deficits, caused decreasing trends in wildfires, especially in arid temperate grasslands. Moreover, increased natural and human ignitions led to increasing trends in wildfires in high-latitude ecosystems, whereas intensified human activities suppressed wildfires in densely populated areas, leading to declining wildfire trends. These results suggest that flammability impacts wildfire trends oppositely depending on fuel conditions, and human ignition has polarized effects on wildfire trends due to varying intensity and direction of human activities. Such interactions contribute to contrasting wildfire trends and imply that warmer climates and human activities will exacerbate contrasting wildfire dynamics. Our study improves the understanding of long-term wildfire trends, aids in exploring terrestrial carbon cycles under climate change, and supports practical wildfire management.