# Multi-ignition fire complexes drive extreme fire years and impacts

## TL;DR

Large fires caused by merging multiple ignitions are a major driver of extreme fire years and increased destruction in regions like California and the Arctic.

## Contribution

The study identifies multi-ignition fire complexes as a key mechanism amplifying fire size and impact, using satellite data from 2012 to 2023.

## Key findings

- Multi-ignition fires account for 31% of burned area in California and 59% in the Arctic-boreal domain.
- These fires spread faster, persist longer, and disproportionately contribute to extreme fire years in key regions.
- They generate stronger atmospheric feedbacks and strain firefighting resources due to their complex nature.

## Abstract

Climate change is intensifying fire behavior, with the largest and fastest-spreading fires causing the greatest impacts on people and ecosystems. Yet the mechanisms driving variability and trends in large fires remain poorly understood. Using 12-hour satellite-derived fire tracking data from 2012 to 2023, we show that the merging of separate ignitions into multi-ignition complexes is a key process amplifying fire size and destructive potential across temperate and boreal ecoregions. Multi-ignition fires account for 31% of the burned area in California and 59% in the Arctic-boreal domain, spread faster and persist longer than single-ignition fires, and disproportionately contribute to extreme fire years in California, Canada, and Siberia. They also generate stronger atmospheric feedbacks, produce more pyrocumulonimbus events, and strain firefighting capacity by dispersing suppression resources. Recognizing and accounting for fire-merging dynamics are critical for improving wildfire prediction, risk assessment, and management.

When lightning ignites multiple fires that merge, the resulting complexes spread faster and cause greater destruction.