Widespread climate-driven increases in global wildfire season length (1979-2013) and potential carbon cycle feedbacks

Wednesday, 17 December 2014
William Matthew Jolly1, Mark A Cochrane2, Patrick H Freeborn2, Zachary A Holden3, Timothy J Brown4, Grant J Williamson5 and David M. J. S. Bowman6, (1)US Forest Service Missoula, Missoula, MT, United States, (2)South Dakota State University, Brookings, SD, United States, (3)University of Montana, Missoula, MT, United States, (4)Desert Research Inst, Reno, NV, United States, (5)University of Tasmania, Hobart, Australia, (6)University of Tasmania, School of Biological Sciences, Hobart, Australia
Global wildfire activity is strongly constrained by climate and recent surges in extreme fire events may signal global pyrogeographic changes in response to increased fire weather severity. Using three daily global climate datasets and three fire danger indices, we mapped spatio-temporal trends in wildfire weather season lengths from 1979 to 2013. We found extensive fire weather season lengthening focused within 27.7M km2 (23.7%) of the Earth’s vegetated land surface, resulting in a 16.3% increase in global mean fire weather season length. We also observed a near doubling (90.3%) of global burnable area affected by anomalously long fire weather seasons (>1.0 σ above historical mean) and an increased frequency of long fire weather seasons across 62.3M km2 (53.3%) of the globe’s vegetated areas during the second half of the study period. Strikingly, inter-annual fire weather season length variations were significantly correlated with annual global atmospheric CO2 growth rates (r= 0.42 and r = 0.41, respectively, p < 0.05), consistent with a fire-climate feedback loop.