finding 20.3 : climate-change-increases-wildfires

Increased warming, drought, and insect outbreaks, all caused by or linked to climate change, have increased wildfires and impacts to people and ecosystems in the Southwest. Fire models project more wildfire and increased risks to communities across extensive areas.



This finding is from chapter 20 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: A central component of the assessment process was the Southwest Regional Climate assessment workshop that was held August 1-4, 2011, in Denver, CO with more than 80 participants in a series of scoping presentations and workshops. The workshop began the process leading to a foundational Technical Input Report (TIR) report.17ad4429-1321-4e7c-9cd5-3554eb0c3b38 The TIR consists of nearly 800 pages organized into 20 chapters that were assembled by 122 authors representing a wide range of inputs, including governmental agencies, non-governmental organizations, tribes, and other entities. The report findings were described in a town hall meeting at the American Geophysical Union’s annual fall meeting in 2011, and feedback was collected and incorporated into the draft. The chapter author team engaged in multiple technical discussions through more than 15 biweekly teleconferences that permitted a careful review of the foundational TIR17ad4429-1321-4e7c-9cd5-3554eb0c3b38 and of approximately 125 additional technical inputs provided by the public, as well as the other published literature and professional judgment. The chapter author team then met at the University of Southern California on March 27-28, 2012, for expert deliberation of draft key messages by the authors. Each key message was defended before the entire author team prior to the key message being selected for inclusion. These discussions were supported by targeted consultation with additional experts by the lead author of each message, and they were based on criteria that help define “key vulnerabilities, which include magnitude, timing, persistence and reversibility, likelihood and confidence, potential for adaptation, distribution, and importance of the vulnerable system.”3277e83c-e374-4ed5-b0a2-0adadfaf118d

Description of evidence base: Increased warming and drought are extensively described in the foundational Technical Input Report (TIR).17ad4429-1321-4e7c-9cd5-3554eb0c3b38 U.S. temperatures have increased and are expected to continue to rise (Ch. 2: Our Changing Climate, Key Message 3). There have been regional changes in droughts, and there are observed and projected changes in cold and heat waves and droughts (Ch. 2: Our Changing Climate, Key Message 7) for the nation. A study for the Southwest966bf116-8d6d-41f2-96be-4b66d3e729db discusses trends and scenarios in both cold waves and heat waves. Analyses of weather station data from the Southwest have detected changes from 1950 to 2005 that favor wildfire, and statistical analyses have attributed the changes to anthropogenic climate change. The changes include increased temperatures,8e18883e-9d45-4998-a0dd-bf59bab323ad reduced snowpack,0d8b090e-e060-4f9d-a442-b7e050608a20 earlier spring warmth,56447233-ad64-46b3-8371-925de98e78c0 and streamflow.87875dde-385b-4f57-b0ae-aa21648b2833 These climate changes have increased background tree mortality rates from 1955 to 2007 in old-growth conifer forests in California, Colorado, Utah, and the northwestern states9c23a870-58cf-49f6-9c6f-01cb94e4bb5a and caused extensive piñon pine mortality in Arizona, Colorado, New Mexico, and Utah between 1989 and 2003.70730c1e-50f8-43db-b7b2-4d7ae90ba230 Climate factors contributed to increases in wildfire in the previous century. In mid-elevation conifer forests of the western United States, increases in spring and summer temperatures, earlier snowmelt, and longer summers increased fire frequency by 400% and burned area by 650% from 1970 to 2003.e1e1f3a0-9fea-4ad2-a3af-575716f9849e Multivariate analysis of wildfire across the western U.S. from 1916 to 2003 indicates that climate was the dominant factor controlling burned area, even during periods of human fire suppression.391560e0-40c1-4f9d-b063-e87d18c87e02 Reconstruction of fires of the past 400 to 3000 years in the western U.S.595285a9-a56e-4a77-9c34-aa8f2200daa0 ffd9009a-b9a8-49f3-a713-c7eec55309f3 and in Yosemite and Sequoia National Parks in Californiad9676336-763f-4566-a262-87e7fb0d6e78 3e807297-3ee2-48b8-a3b8-66dc94d0f307 b939c889-e2f4-4e11-ae17-2382a4a2a44b confirm that temperature and drought are the dominant factors explaining fire occurrence. Four different fire models project increases in fire frequency across extensive areas of the Southwest in this century.37982de0-0e01-476f-b522-b8162d709134 f26bec89-45ef-4609-adfe-0c0e6f41041c 81f7dc22-574e-4135-b6f1-882762ea580f 8dfecf8b-f8a8-4f03-8d68-551b13794a1d Multivariate statistical generalized additive models78ccfd46-befc-4726-8dea-985aa6efb5b8 f26bec89-45ef-4609-adfe-0c0e6f41041c project extensive increases across the Southwest, but the models project decreases when assuming that climate alters patterns of net primary productivity. Logistic regressions8dfecf8b-f8a8-4f03-8d68-551b13794a1d project increases across most of California, except for some southern parts of the state, with average fire frequency increasing 37% to 74%. Linear regression models project up to a doubling of burned area in the southern Rockies by 2070 under emissions scenarios B1 or A2.81f7dc22-574e-4135-b6f1-882762ea580f The MC1 dynamic global vegetation model projects increases in fire frequencies on 40% of the area of the Southwest from 2000 to 2100 and decreases on 50% of the areas for emissions scenarios B1 and A2.37982de0-0e01-476f-b522-b8162d709134 Excessive wildfire destroys homes, exposes slopes to erosion and landslides, and threatens public health, causing economic damage.eeb3d1ca-6070-44f5-8f9f-e1fa7a2aeb19 a0e75d55-c3b6-4a44-805b-ef3460afd925 4ee18e43-0d8d-4276-ad51-b87db1d8b7bc e6ca6d9a-a57e-424b-b4b5-3a6ea6eed51d Further impacts to communities and various economies (local, state, and national) have been projected.8dfecf8b-f8a8-4f03-8d68-551b13794a1d

New information and remaining uncertainties: Uncertainties in future projections derive from the inability of models to accurately simulate all past fire patterns, and from the different GCMs, emissions scenarios, and spatial resolutions used by different fire model projections. Fire projections depend highly on the spatial and temporal distributions of precipitation projections, which vary widely across GCMs. Although models generally project future increases in wildfire, uncertainty remains on the exact locations. Research groups continue to refine the fire models.

Assessment of confidence based on evidence: There is high confidence in this key message given the extensive evidence base and discussed uncertainties.

References :

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