Abstract
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° 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°–60° 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.
Highlights
Accepted: 6 May 2021In recent years, large wildfires have affected human communities throughout central and southern Chile along the subtropical Mediterranean and transitional-temperate west coast of South America
600,000 hectares in central Chile, the largest area burned during a single fire season since detailed records of fire activity began in the 1960s [1]
While changing climatic and biophysical conditions, land-use transitions, and changes in the vegetation and fuel characteristics are all thought to be partially responsible for these large fires [2,3], the role that broad-scale surface and atmospheric conditions play in driving the spread of large fires is still not well understood
Summary
Large wildfires have affected human communities throughout central and southern Chile along the subtropical Mediterranean and transitional-temperate west coast of South America. ‘megadrought’ [14] helped create the conditions for the occurrence of recent large fires in south-central Chile, the broad-scale (i.e., thousands of kilometers) climatic conditions associated with years of anomalously high (or low) area burned have not been well examined. These include synoptic-scale conditions that promote extreme fire weather including unstable air, low relative humidity, strong surface winds and high temperatures [1,6,20]. Indicated is the westerly wind belt (WWB) and the center of the subtropical anticyclone (H) (1b)
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