Wildfires and Climate Change in the Western US

Transcription

1 Wildfires and Climate Change in the Western US Biscuit Complex Fire, July 13 Sept. 5, 22, 499,965 acres 22 Megafires in the Western U.S Hayman Fire, June 8 July 2, 22, 138, acres Thomas W. Swetnam Laboratory of Tree-Ring Research The University of Arizona Tucson, Arizona Rodeo-Chediski Fire, June 18 July 7, 22, 463, acres More than 3.7 million acres burned in Texas, December 25 to March 26; more than 55, acres burned in Oklahoma since November 25 Fire in Iceland, March 3, 26 It took four days to control, and it burned somewhere around 67 square kilometers, the largest fire recorded since the island was settled in the 9th century. NASA MODIS Wildfires in 26 have burned more than 8.7 million acres as of the end of September. That acreage is roughly equal to the land areas of Massachusetts, Connecticut, and Rhode Island combined! This year already ranks as the U.S.'s worst wildfire season in nearly a half-century, according to the Interagency Fire Center. The 8.7 million acres burned for the whole U.S. as of late September tops the 25 record of 8.69 million acres (record since 196). Day Fire near Ventura, CA, Sept.3 1

2 About 3.5 million acres burned in AZ & NM between 21 and 25. The total forest area of the SW is about 2 million acres. So, about 18% of the forest area burned in 5 years! Biondi, F Ecological Applications 9: Aspen Fire, June 23 Rodeo- Chedeski Fire June 22 Swetnam, T. W Fire history and climate change in giant sequoia groves. Science. 262:

3 The Southwestern US network of fire scar sites shows a high degree of regional fire synchrony and as expected, the largest and smallest fire years are well correlated with dry and wet years, respectively. Swetnam & Baisan 23 Livestock Grazing/Fire Suppression Era Legacy of Livestock Grazing RAILROADS led to > 5 million sheep and 1.5 million cattle in New Mexico by 189 Environmentally beneficial years Environmentally stressful year Drought sensitive tree-ring width chronologies are calibrated with instrumental-based records of Summer Palmer Drought Severity Index, and interpolated to an evenly spaced grid network. Courtesy of David Stahle Cook, E.R., C.A. Woodhouse, C.M. Eakin, D.M. Meko, D.W. Stahle. Science 36: Nov

4 Calibration/Verification Reconstruction Regional large and small fire years in the Southwest are strongly linked to wet and dry conditions. 4 Small Fire Years (<4 sites recording fire) Large Fire Years (>2 sites recording fire) WET Very Wet! Summer PDSI DRY Data from Cook et al. Science 36: Nov. 5 24, graphic courtesy of David Stahle Year Percent of Western US area under drought (<-3. PDSI) for years 2-24 = 42.3% Highest of any 5-year interval since WESTERN USA DROUGHT TREND: Percent of Area with Palmer Drought Severity Index < y = x R=.232* p<.5 2-tailed YEAR Data from Cook et al. 24, and Henry Diaz, NOAA The warmest years in the instrumental record have occurred in the past decade, and 25 set another record. Temperatures are increasing in most places globally. 4

5 Global and western air temperatures warmed notably in the 2th Century. Spearman s r =.76, p <.1 From Dettinger & Cayan: Spearman s r =.76, p <.1 Spearman s r =.76, p <.1 Continental-scale tree-dieoffs are occurring, including the largest bark beetle outbreak in recorded history in North America, in British Columbia. Warming trends are strongly implicated in this outbreak. More than 2 million acres of dead and dieing trees. Acres (1,) British Columbia Lodgepole Pine Year Photo: Allan Carrol, CFS 5

6 USFS surveys for insect and disease, cumulative map of affected areas for , highlights forest dieback in Western mountains. In some areas and ecosystems the fire problem is more about choices that people have made on to where to live and build structures, rather than about changes in vegetation or climate. Chaparral Wildand Urban Interface, Southern California, 24 Note trend. Acres (1,, Total for survey in the Western US Year Spruce-fir forest & telescopes, Mt. Graham, AZ, 24 How can we make our forests more resilient to the effects of climate change? Prescribed fires and judicious forest thinning can reduce wildfire severity. Example of areas pre-treated before 22 Rodeo-Chedeski Fire. We have almost reached a political tipping point in acceptance of the problem. When will a climate tipping point occur? When will we take serious action? 6

7 Reduce Global Warming! 7