Broad-Scale Surface and Atmospheric Conditions during Large Fires in South-Central Chile

The unprecedented size of the 2017 wildfires that burned nearly 600,000 hectares of central Chile highlight a need to better understand the climatic conditions under which large fires develop. Here we evaluate synoptic atmospheric conditions at the surface and free troposphere associated with anomalously high (active) versus low (inactive) months of area burned in south-central Chile (ca. 32-41 degrees S) from the Chilean Forest Service (CONAF) record of area burned from 1984-2018. Active fire months are correlated with warm surface temperatures, dry conditions, and the presence of a circumpolar assemblage of high-pressure systems located ca. 40 degrees-60 degrees S. Additionally, warm surface temperatures associated with active fire months are linked to reduced strength of cool, onshore westerly winds and an increase in warm, downslope Andean Cordillera easterly winds. Episodic warm downslope winds and easterly wind anomalies superimposed on long-term warming and drying trends will continue to create conditions that promote large fires in south-central Chile. Identifying the mechanisms responsible for easterly wind anomalies and determining whether this trend is strengthening due to synoptic-scale climatic changes such as the poleward shift in Southern Hemisphere westerly winds will be critical for anticipating future large fire activity in south-central Chile.

Automated summary

The study found that active fire months in south-central Chile are correlated with warm surface temperatures, dry conditions, and the presence of circumpolar high-pressure systems. Additionally, warm surface temperatures in active fire months are linked to weakened cool westerly winds and increased warm easterly winds from the Andean Cordillera. These conditions, compounded by episodic warm winds and easterly wind anomalies, will continue to create a conducive environment for large fires in south-central Chile.