Cliff Mass has joined the ranks of those who want you to believe that California’s wildfire problem isn’t getting worse.
He starts (his blog post here) by saying that the number of fires in California has decreased over the last several decades, and claiming that any increase in area burned has not been significant. His “analysis” amounts to this:
For the same 30 years (1987-2016), wildfire area has grown slightly, with huge transient peaks and troughs (see below). With such variability, I suspect the trend would not be significant. Final statistics for 2017 are not yet available on the CALFIRE website.
You “suspect”? Did you not do the math? Do you not know how?
Question for you, Cliff: if you didn’t do the math, if you only “suspect,” then why do you later say “area burned has not been increasing”?
I did the math. One thing that’s clear is that the variation doesn’t follow the normal distribution, so a robust trend test is in order. I like the non-parametric Theil-Sen estimate, and it gives a p-value of 0.0497. For the sake of Cliff Mass and other folks who may not know what a p-value is, it’s the chance of seeing that much change just from an accident of randomness. So yes, Cliff, the trend is significant.
But wait, there’s more. That’s only the data through 2016. Cliff notes that data for 2017 aren’t yet final, and of course neither are numbers for 2018. But in fact there is data for 2017. CalFire notes that “Statistics may not include wildfires in State Responsibility Area protected by CAL FIRE’s contract counties.” so the 2017 number may not be the total, but it’s safe to take as a lower limit — the area burned is at least that much. As for 2018, CalFire notes that we’ve had 749,770 acres burned through August 5th of this year, so again we have a lower limit, this year’s burn area will be at least that much. It’s likely to be a lot more, since we’re less than half-way through August but the traditional “fire season” is September-October.
Let’s include those lower-limit numbers in the analysis. It will, of course, bias the result against a significant trend in area burned — but hey, Cliff Mass and his claims need all the help they can get.
Result: the p-value is 0.017. That’s significant at the 98.3% confidence level. And remember, that’s allowing a “cheat” which favors Cliff Mass’s proposition, by using only lower bounds for 2017 and 2018 rather than final numbers.
On a side note: as of yesterday, the Mendocino complex alone had consumed 304,402 acres — more than the whole-state totals for 10 of the 32 years Cliff Mass uses. But don’t worry, Cliff Mass says “area burned has not been increasing”.
Climate scientists say that climate change is a big factor in the increase of California wildfire. The leaders of CalFire say that climate change is a big factor in the increase of California wildfire. The veteran firefighters on the ground, the ones risking their lives, say that climate change is a big factor in the increase of California wildfire. Cliff Mass — the guy who “suspects” there’s no significant trend — tells me “area burned has not been increasing”.
Do drop on by, Cliff. Be sure to mention the number of fires and that paper by Keeley and Syphard; I’d love to discuss them. But first things first: we want to know whether you still think that area burned has not been increasing.
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