Spatio-Temporal Linkages between Declining Arctic Sea-Ice Extent and Increasing Wildfire Activity in the Western United States

Abstract

Abstract:We examined relationships between monthly Arctic sea-ice extent (ASIE) and annual wildfire activity for seven regions in the western United States during 1980-2015 to determine if spatio-temporal linkages exist between ASIE, upper-level flow, and surface climatic conditions conducive to western U.S. wildfire activity. Winter ASIE had significant (p < 0.05) negative relationships with annual wildfire area burned (r s = −0.391 − −0.683), with the strongest relationship occurring in the Northern Rockies. We explored spatial linkages between ASIE and 300-hPa flow (+), temperature (+), precipitation (−), and soil moisture (+) using monthly values of ASIE and gridded values for the climatic parameters. Relationships were best expressed between January ASIE and conditions in the current-year July over the Pacific Northwest and Northern Rockies. Reduced wintertime ASIE is teleconnected with increased ridging in summertime 300-hPa flow over the western U.S., resulting in warmer and drier conditions during peak fire season. Our findings suggest that reductions in ASIE are one of the driving forces behind the increasing annual trend (>36,000 ha) in area burned in the western U.S. since 1980.

Decreasing fire season precipitation increased recent western US forest wildfire activity

“…One potential mechanism for reduced summertime precipitation is the rapid decline in arctic sea ice extent (27) and subsequent weakening of zonal winds (28), which lead to slower progressions of summertime upper-level waves and promotes more prolonged midlatitude US droughts like those noted in this study. Wintertime arctic sea-ice extent has been linked to western US midsummer precipitation and temperature extrema variations and it has been suggested as one of the driving factors in burned area increases (29). The degree to which precipitation decreases noted in this study are connected to weather changes associated with shrinking arctic sea ice is unknown.…”

North American Weather Regimes Are Becoming More Persistent: Is Arctic Amplification a Factor?

“…While many recent studies have investigated the atmospheric response to Arctic sea ice loss (e.g., Cvijanovic et al, 2017;Deser et al, 2016;Knapp & Soulé, 2017;Kug et al, 2015;Lee et al, 2015;McCusker et al, 2016;Meleshko et al, 2016;Nakamura et al, 2015;Sorokina et al, 2016;Sun et al, 2016;Sung et al, 2016;Wang et al, 2018), the question of whether AAW is affecting the persistence of weather regimes has received little attention. The duration of various weather types has been explored (e.g., Screen, 2013;Screen et al, 2015;Zolina et al, 2013) with some indications that persistence has increased during summer in midlatitudes (e.g., Coumou et al, 2018;Pfleiderer & Coumou, 2017) while changes have varied in other seasons and regions.…”

Divergence of Arctic shrub growth associated with sea ice decline

“…Sea ice decline has elicited major changes in local climates and large-scale atmospheric circulation ( 7 ), extending beyond the regions of in situ sea ice changes ( 8 ). This includes the impact of winter SIE on upper-level atmospheric flow and subsequent summer air temperature, precipitation, and even soil moisture ( 9 ). While this rapid change in the physical system is occurring, the mechanisms by which Arctic sea ice interacts with biological systems are still largely unknown, especially in terrestrial systems ( 10 ).…”