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- Title
Compound Extremes Drive the Western Oregon Wildfires of September 2020.
- Authors
Abatzoglou, John T.; Rupp, David E.; O'Neill, Larry W.; Sadegh, Mojtaba
- Abstract
Several very large high‐impact fires burned nearly 4,000 km2 of mesic forests in western Oregon during September 7–9, 2020. While infrequent, very large high‐severity fires have occurred historically in western Oregon, the extreme nature of this event warrants analyses of climate and meteorological drivers. A strong blocking pattern led to an intrusion of dry air and strong downslope east winds in the Oregon Cascades following a warm‐dry 60‐day period that promoted widespread fuel flammability. Viewed independently, both the downslope east winds and fuel dryness were extreme, but not unprecedented. However, the concurrence of these drivers resulted in compound extremes and impacts unmatched in the observational record. We additionally find that most large wildfires in western Oregon since 1900 have similarly coincided with warm‐dry summers during at least moderate east wind events. These results reinforce the importance of incorporating a multivariate lens for compound extremes in assessing wildfire hazard risk. Plain Language Summary: Several very large fires in western Oregon spread rapidly during an unusually strong offshore wind event that commenced on Labor Day in 2020. The Labor Day fires burned more area of the Oregon Cascades than had burned in the previous 36 years combined and very likely exceeded the area burned in any single year for at least the past 120 years. The fires damaged over 4,000 structures, led to several fatalities, placed over 10% of the state's residents under some level of evacuation advisory, and contributed to the hazardous air quality across the Northwestern United States. A compound set of weather‐related factors leading up to and during the fires facilitated these extreme fires. Unusually warm conditions with limited precipitation in the 60‐days leading up to the fires allowed for fuels to become particularly dry and combustible by early September. Downslope offshore winds materialized during September 7–9, 2020 across the Oregon Cascades bringing exceptionally strong winds and dry air that drove rapid rates of fire spread. While neither of these individual factors was unprecedented, the concurrence of these drivers created conditions unmatched in the observational record. Key Points: Approximately 11% of the Oregon Cascades burned during September 7–9, 2020 coincident with strong offshore downslope windsUnprecedented compound extremes involving fuel aridity and fire meteorology facilitated the extent and spread of firesVery large fires in western Oregon since 1900 have generally occurred during east wind events at the end of anomalously warm‐dry summers
- Subjects
OREGON; WILDFIRE prevention; FIRE management; FOREST fires; WILDFIRES; LABOR Day; WILDFIRE risk; AIR quality; FLAMMABILITY
- Publication
Geophysical Research Letters, 2021, Vol 48, Issue 8, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2021GL092520