Very Large Wildland Fires Predicted to Increase in Rocky Mountains and Pacific Northwest

by Emil Morhardt

In the middle of one of the worst fire seasons on record for Northern California comes a new modeling paper by scientists at CalTech’s Jet Propulsion Laboratory, the University of Idaho, and the US Forest Service Pacific Wildland Fire Sciences Laboratory predicting no effect of climate change on Northern California Very Large Wildfires (VLWFs), but potentially large increases in them in the Pacific Northwest and Rocky Mountains under future greenhouse gas (GHG) emissions scenarios. It may well be that the size of the Northern California fires won’t reach the threshold of 50,000 acres used in this study (the top 2% of wildland fires), but if these not-so-large fires are disturbing, then the prospect of even larger ones more frequently in much of the western US is even more so.

The important factors according to the models are the future levels of GHGs, potential fuel load, and dryness (the latter of which is driving the current Northern California fires). In the Pacific Northwest, what maters most is dryness; this region has plenty of fuel on hand, but is flammability-limited by moisture. The western great basin (which I’m looking at out the window just now) is fuel-limited; we didn’t have much rain this year, so not much fuel was added. The Southwest has the advantage that it gets summer monsoons, which, when they arrive, dramatically decrease the possibility of wildfires.

The study is elegantly done, using an ensemble of 14 climate models to determine regional uncertainty in climate predictions, two GHG scenarios bracketing what is likely up to 2100, and using observed climate data going back to 1979 to calibrate the fire probability models against the various climate variables that the models predict. The most striking results to me are not the somewhat comforting lack of predicted increased VLWFS in Southern and Northern California, but the fact that places with currently cooler wetter climates like the Pacific Northwest and the Rocky Mountains are likely to have many more highly destructive fires as the century progresses.

 

Stavros, E.N., Abatzoglou, J., McKenzie, D., Larkin, N.K., 2014. Regional projections of the likelihood of very large wildland fires under a changing climate in the contiguous Western United States. Climatic Change, 1-14. DOI 10.1007/s10584-014-1229-6 First 2 pages from Springer: http://bit.ly/1CPcfCT

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