U007-03
Regional climate feedback exacerbating wildfires in western United States

Wednesday, 9 December 2020: 10:50
William K-M Lau, Earth System Science Interdisciplinary Center, College PARK, MD, United States; University of Maryland College Park, Department of Atmospheric and Oceanic Sciences, College Park, MD, United States, Lei Zhang, U. of Maryland, Atmospheric and Oceanic Sciences Department, College Park, MD, United States, Weichen Tao, Institute of Atmospheric Physics, Beijing, China and Zhanqing Li, University of Maryland, Atmospheric and Oceanic Sciences Department, College Park, MD, United States
Abstract:
Dubbed as “The Year the World Burned”, 2019 witnessed the record outbreak of devastating wildfires around the globe, notably in Australia, western United States, the Amazon, Siberia, Indonesia, Lebanon, and many other regions. In 2020, wildfires have continued at abnormally high levels in these regions. The widespread global wildfires have been suggested to be associated with greenhouse gases (GHG) global warming. However, the impact of regional climate feedback processes on increasing frequency and severity of wildfires remain poorly known. Detecting regional effects of GHG warming is challenging, due to relative short record of reliable data, and confounding effects of natural climate variability.

In this paper, we have conducted an analysis of wildfire-climate relationship over North America using diverse observation and reanalysis datasets for the period 1984–2014. Results show that the western US (WUS) has experienced the most robust increase in burned area, even though Alaska and western-central Canada have stronger warming trends. Additionally, the WUS has been under the influence of significant multi-decadal trends in tropospheric relative humidity deficit, reduced cloudiness, increased surface net insolation, enhanced adiabatic warming and drying from increased mid-tropospheric subsidence and from enhanced off-shore low-level flow. These trends detected in our relatively short data record, while consistent with climate model projection of GHG-induced widening of the descending branch of the Hadley Circulation, are likely also contributed and confounded by natural inter-decadal climate variability.

Overall, our results suggest that GHG warming is a necessary but not sufficient condition for long-term trends in large wildfires around the globe. Rather, regional radiation-circulation dynamic feedback processes, sustaining the warming and drying of the troposphere, on scales substantially larger than the wildfire burnt areas themselves are essential. Our “balance-of-evidence” and process-oriented approach, using diverse, independent observations, multiple re-analyses, and guidance from climate model projections, can be used for detection and better understanding of regional climate feedback processes, exacerbating wildfires in different climatic regions of the world.

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