October 30, 2017

Why the Wine Country Fires Was a Severe Weather Event and Not Climate Change

For an extended analysis, check out my new blog on the topic found here.

Politicians, climate activists, and some media outlets have claimed that there is a strong connection between the recent Wine Country fires north of San Francisco and global warming forced by increasing greenhouse gases.  Some samples (could provide dozens more):
MIT Review

Washington Post
However, if one studies the meteorology of this event, the history of wildfires in the region, changes in the population and land use, and some basic wildfire principles, one is compelled to come to a very different conclusion:

Climate change had little to do with the initiation and severity of the fire.

The truth is that this was a severe weather event, whose terrible impacts (at least 43 dead and tens of billions of dollars of damage) were greatly magnified by poor societal decisions, inadequate planning, poor management of vegetated areas, ineffective use of forecasts, and inappropriate development.

An Extreme Weather Event

The wildfires that hit Santa Rosa and other communities began shortly after a sudden surge of strong winds in the early evening of Sunday, October 8th.  At the Santa Rosa RAWS observing location, winds rapidly increased that evening around 9 PM PDT and reached a peak of 68 mph around 5 AM PDT, after which they dropped rapidly (see graphic).

 A map of the maximum gusts that night at higher elevations (see below) shows 108 mph in the mountains NE of Geyserville at 3450 ft, and 79 mph at the nearby  (and lower) RAWS site (Hawkeye, 2000 ft),  The relatively low (550 ft) Santa Rosa RAWS location had 69 mph, but the Atlas Peak site to the east only reached 34 mph.  This will be important.

A map of the maximum gusts, mainly from lower-elevation sites based on the NWS MADIS collection, is shown below (the graphic created by UW grad studentConor McNicholas).  Note these are in knots (multiple by 1.15 to get mph)  Many of lower elevation sites got to 30 knots (35  mph), with higher winds (40 knots plus at sites in or to the lee of terrain). A few sites got into the 60s.

Now it would have been nice to have more observations (especially at altitude), but the observations we do have suggest moderate gusts of 30-40 mph at lower elevations, but MUCH higher winds near the mountain crests and immediately downwind of the crests (60-110 mph).  The winds distribution was complex and as shown at Santa Rosa (and elsewhere), the winds came up very quickly around 9 PM, only to subside by daybreak.

As I described in my earlier blog, numerical models provided realistic simulations (and forecasts) of this event.  Really quite impressive. As a modeler myself, I have been working with experienced UW WRF modeler Dave Ovens to simulate this event at very high resolution (1.3 km grid spacing).    Let me show you a bit of what we found.  

The next graphic shows you the forecast winds at about 1000 ft above the surface (which should provide a measure of the max gusts) at 11 PM on Oct 8 (the forecast started at 11 AM that morning).  A terrain map is provided for reference.  

You notice there is a lot of structure to the wind with highest values over the higher terrain and the upper lee slopes.  Winds of 60-65 knots above Santa Rosa. 70-75 knot winds were forecast NE of Geyserville, just where the max winds were observed.

 As I noted in my earlier blog, the regional winds from the NE strengthened as cool air and high pressure built to the northeast (eastern Oregon, NE CA).  But something special occurred on top of that: huge wind acceleration over and downstream of the local terrain.    To show this, let me show you a vertical cross section from the WRF model forecast for 9 PM Sunday, just as things were really revving up.  The path of the cross section is shown by the black line below.

Below is the cross section.  You can see the terrain, sustained winds by the colors, and the solid lines are something called potential temperature.

Wow.  The low-level winds were from the east and greatly accelerated at and west of the crests...in some places to over 70 knots (81 mph)!  Keep in mind this was a 10-hr forecast, so strong winds were expected.  Other modeling systems did the same thing (e.g., NOAA HRRR, Desert Research Institute/CANSAC WRF).

Why were the winds increased so much by terrain?   This is what meteorologists call a downslope wind event with a structure that represents what we call a hydraulic acceleration and jump.    This is like water going over a dam and accelerating down the dam's slope.

There was relatively cool, dense air upstream of the terrain and a stable layer/inversion right above.  This kind of atmospheric structure really helps produce such acceleration.   And small changes in the upstream structure can radically change the winds--you have to get it just right to get the big acceleration.

The conditions that night were ideal to get strong winds over and downwind of the terrain east of Santa Rosa and Geyserville.   And it appears highly predictable by state of the art models.  We know this was an unusual situation because several of the observing sites mentioned above had record-breaking winds that night (at least as far back as the records went: 1991)

In summary, this was an extreme weather (wind event).  There is no denying that.

Why Global Warming Can't be to Blame

Here is why.

(1) Strong downslope winds over northern California are not expected to increase due to global warming

There is no reason to expect that the strong winds had anything to do with global warming.  The winds were produced by COLD air moving into the intermountain west, and one would expect that global warming would moderate those temperatures, lessening wind potential.  Furthermore, research by my group and others have shown a deamplification of large scale weather disturbances during the warm season, something that is not surprising considering the weakening of horizontal temperature differences by global warming.

(2)  Warm temperatures and drought

A number of politicians, media folks, environmental activists, and others have thrown out the argument that droughts and unusually warm temperatures HAD to have contributed to the fires.  However, a more careful analysis reveals that this CAN'T be the case in respect to the recent fires.

First, one must ask what was the main vegetation involved in the fires.  It was mainly grass, not bushes and trees.  Picture after picture demonstrates this, and in many burned locations the trees are still alive and green (see below).

Picture courtesy of Jim Steele

Picture courtesy of CA National Guard

There was more grass than normal going into this summer because of excessive rain, NOT DROUGHT, this last winter.  Climate models do not suggest massive increases of rainfall over northern California under global warming.  And observed rainfall over the past decades indicate no such trend.

And the dry conditions this summer is absolutely typical for northern California, where rains are generally absent from May to October.

But what about temperatures?   Could warm temperatures this summer have contributed to the fires by drying out the vegetation more than normal.  The answer is no...and let me tell you why.  It is true that this summer was warmer than normal in California, but average summer conditions are plenty warm to do all the drying needed.

The U.S. Forest Service considers grasses 1-h fuels, meaning the dry/warm conditions can sufficient remove the moisture in hours, allowing them to burn.  And bushes are generally 10-hr fuels.    This was the end of the summer.  There was plenty of time to dry out all the vegetation and a few degrees of warming had no impact--the excessive warmth was immaterial.  A normal summer would have done the drying job fine.

Take a look at the 10-hr fuel moisture for Santa Rosa for the past five years...no real trend.  The moisture goes up in the winter and down in the summer, with no obvious trend on the low side.

Why Blaming Climate Change for the Fires is a Bad Idea

Blaming global warming is a convenient excuse not to deal with the real problems that produced these fires:

  1. Large number of homes and structures have been built in the Santa Rosa/Napa region over the past 50 years, with population going up by roughly five times.  Many were built in bad locations in the forest/urban interface or actually in the forests.   Major housing developments were built in regions that had experienced catastrophic wildfires relatively recently.
  2. Fire has been suppressed in the surrounding vegetated hills, results in the build up of dangerous fuel loads (dry vegetation).  A catastrophe ready to happen.
  1. The electrical system was vulnerable to winds, resulting in the ignition of fires.  Furthermore, there have been several suggestions that PG&E has not properly maintained its powerline right of ways.
  2.  Inadequate use of state-of-the-science weather prediction results in a lack of timely warning of a catastrophic situation.
  3.  Lack of  robust building codes for a fire-endangered region.
Some politicians are using global warming as a tool for making political points and to avoid the expensive and costly changes required to address this threat.

Global warming due to increasing greenhouse gases will cause many changes, many of them bad, by the end of the century.  But blaming unrelated environmental catastrophes on global warming greatly undermines attempts to make the real changes and sacrifices need to prevent such tragedies in the future.

It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so.     Mark Twain


  1. When will we know that weather is from climate change?

  2. You rock! Thanks for breaking it down and explaining exactly why you think it's such a bad idea that we attribute this tragedy to climate change. Aren't we lucky too that KNKX had the wisdom and vision to bring you on. Kuow is becoming such a downer. They can't even honor free speech. They have to apologize anytime they give someone's POV airing that dares to stray beyond a very narrow perspective and offend a few people. tisk tisk. More pablum please. but I digress :-) bottom line - it really does have much to do with free and critical thinking and the forum to communicate those thoughts for the greater good. Thanks!

  3. Cliff - using soil moisture to assess whether fuels were dry is unfair. You can have dry soils with wet vegetative and vice versa. A quick search online turned up the National Fuel Moisture Database, which measures the moisture in the local vegetation. 2017 moisture was indeed much lower than previous summers likely due to the very warm conditions. Here is a table for a location near the fire region http://www.wfas.net/nfmd/public/site.php?site_fuel=Trough%20-%20Old%20Growth&gacc=NOCC&state=CA&grup=Mendocino%20NF&sitefuel=site&display_type=Table%20Only%20Bi

    I agree that the wind event can not be attributed to climate change, but think the antecedent conditions that resulted in the explosive fire growth and behavior can to some extent. Yes, infrastructure and fire mismanagement were a bigger factor though

  4. Very good analogy! Well thought out and presented with, as Jack Webb always liked to say: "Just the facts"! Sadly, those who are given to blame global warming (or the now more prevalent global climate change meme) are willfully not seeing the forest for the trees. Thanks Cliff for once again presenting a level headed answer to what was a truly devastating disaster. Hopefully it will not go unheeded.

  5. Jeff.... it WAS fuel moisture, so I think the analysis is fine. Typo in the text but the figure was correct..Fixed...cliff

  6. MUCH RESPECT for posting the truth! I'm sure that it isn't always helpful to the career.

  7. Great article.

    I have lived in SoCal nearly all my life and these wind events (Santa Anas) are quite common in fall and winter here, with the fall events being associated with many of our most destructive fires.

    I note Cliff mentions that the inland air needs to be relatively cool to initiate the wind event. I have also read that if that inland air is insufficiently cool, the offshore flow may still heat up the coastal areas but there will not be as much wind.

    My gut feeling in SoCal vs. 50 years ago is that the latter type heat events are more common now but the Santa Ana type events are less common. Last week's World Series heat was a Santa Ana event. It was 85F with strong winds at 6AM on Oct. 24 where I live near the Verdugo Mountains. While a few areas like mine had low temps over 80F, many other areas in SoCal had low temps near 70F even though the whole region was 100-106F during the day.

  8. The media hysteria for blaming climate change for every fire, hurricane and flood needs to stop. I understand they want ratings and to sell newspapers but they either lack the knowledge to make such claims or they're not being objective when talking to sources, ie, they tend to get their information from biased climate change activists. Speculation isn't scientific fact and it's so easy to blame every major weather event on climate change but we have to remember that the strongest storm ever recorded was almost 40 years ago (Typhoon Tip) and who knows how many stronger storms before records were kept and before humans were around.

  9. Yes, writers of headlines are notorious for, well, writing attention grabbing headlines of course. There is an old saying that goes something like this:


    The listed headline regarding Clinton is from a WP article that essentially agrees with much that Cliff Mass has detailed about the recent northern California event. Wet spring, dry summer, lotsa bush etc. It then expands into a more generalized theme of state wide trends:

    "How might climate change overlap with this? It’s tempting to cherry-pick data that suggests a role for climate change that’s hard to prove. We do know, however, that some of what the state experienced this year lines up with what climate models would predict."

    The article in question and the statements by Clinton are more focused on fire trends, western states wide and over considerable time. The association of this trend of fires to climate change is succinctly summarized in the the following sentence:

    "The key word there is exacerbating. Clinton wasn’t saying the fires were caused by climate change, just that climate change may have made them worse."

    An examination of the other headline mentioned (from MIT) shows another equally nuanced framing, again aligned with Cliffs own observations, that has to do with statewide or global fire and climate trends, not this single event, wisely predicated by language such as:

    "Whether climate change is a contributing factor to any single fire in California is almost beside the point. By now we know it does contribute to fires and will exacerbate many more extreme events, as climate scientists have long predicted, steadily increasing costs, damage, and deaths."

    Again, very much aligned with what Cliff himself often says - steadily increasing climate change effects and associated costs, likely becoming catastrophically beyond anything of the current norm, not now but off in the future.

    I won't burden this blog with any more cut and paste evidence, suffice to say that if you fully read the articles yourself - which isn't easy, no links being provided - you will see what I mean. Language must be fully utilized, if one is interested in something more than the inherent deception of Trump tweets. In this case, as with most, you really need to


  10. Cliff - Glad I found a typo, and your analysis does make more sense now, though I would argue that your assumption that these fires relied only on dry grass/brush is false. I saw lots of video footage and photos of burning trees. The dryness of the trees is much more closely aligned with the WFAS index I linked to than the 10-hr fuels you reference. The WFAS index shows drier fuels compares to prior years, which is possibly linked to climate change and the very warm summer in CA

  11. Anne - "and who knows how many stronger storms before records were kept and before humans were around."

    Of course there were thousands, perhaps millions of stronger storms! We've been around a few decades and we think we're so smart. We know NOTHING.

  12. Bruce you are trying to cover for blatant climate demagoguery. After carefully reading and noting what is omitted in WAPO and other media hype, we find numerous politicians and journalists pushing a total misconception that climate change is making fires worse, or making the fire season longer, or fires more intense, exacerbate, etc etc

    But the "tell" of their intentions is they ignore or down play what forest ecology research shows. There are no details about fire history with more fires in the past, or that fire suppression caused fuel build ups, and poor landscape management that exacerbated the problem, and how increasing populations lead to increasing human started fires that start with less dryness.

    What must be read is forest and fire ecology research such as http://www.pnas.org/content/114/11/2946.full.pdf

    "In a 2017 paper researchers reported that across the USA from 1992 to 2012, “human-caused fire season was three times longer than the lightning-caused fire season and added an average of 40,000 wildfires per year across the United States. Human-started wildfires disproportionally occurred where fuel moisture was higher.” Furthermore “Human-started wildfires were dominant (>80% of ignitions) in over 5.1 million km2, the vast majority of the United States, whereas lightning-started fires were dominant in only 0.7 million km2.”

    If the climate demagogues were sincerely trying address the causes and increased intensity of fires they would address the real problems, those real problems would be in the headlines, but they seldom offer more than lip service to critical factors to couch their climate extremism

  13. Interesting. Reminds me of studying at the U.W. in 2005, and learning about the air pollution created in China, that makes its way in the upper atmosphere from China to us. We were taught to do research and look for facts and the truth. Thank you for shedding light on the truth here.

  14. No Jim Steele, I mean what I said - no need for you to infer anything else. The 2 headline examples used to preface the entire blog argument that there exists an abundance of hyperbolized hysteria about any single fire events caused by global warming is not substantiated by the actual articles. Neither the cited claims of Hillary Clinton or the article authors spend much energy invoking any single fire events, no matter what the reader might think from the fairly routine headlines.

    I don't doubt that somewhere out there in pop media land someone could find examples of what Cliff is getting at, but these two simply are not that. From what I can tell, they are not the outliers either. These two articles are fairly representative of how the California fires are portrayed, at least by respected sources, in a context of climate change. There is no great stretching of any truth and great pains are taken to illustrate the great complexity of contributing factors and inherent uncertainty that that implies, which hardly rates as your claim of "climate extremism' now does it?

    Unless of course this one defining statement is what you find extreme:

    ""Whether climate change is a contributing factor to any single fire in California is almost beside the point. By now we know it does contribute to fires and will exacerbate many more extreme events, as climate scientists have long predicted, steadily increasing costs, damage, and deaths."

    If there is one repeated error in the mainstream media narrative it is the general absence of this message that the subtle hints detected now have implications for the future. No there is hardly any evidence of global warming as a substantive cause of these fires at this time. What is important is that the tiny contribution that is detectable today is a warning of what is coming down the pipe. Whatever we see today, be it fires, sea level, rain or drought is peanuts compared to what we will hand off to our kids.

  15. So many people seem not to know the difference between weather and climate. Whatever happens, it will always be a weather event when it does.

  16. I challenge Prof. Cliff Mass to debate UW Prof. Dan Jaffe about whether a multitude of weather events (around the world) occurred, during the past 50 years, which were likely at least partially caused by human-caused global warming. I prefer a refereed debate, held perhaps at UW's Meany Hall. The winner is awarded a trophy, and the loser agrees to not present, post or publish anything about climate change or global warming for one year.

  17. Stephen Fry,
    Professor Jaffe and I are friend and talk about these issues all the time. I don't think we disagree on the science. Please tell me what I got wrong. What technical issue have I made a mistake on? I will be happy to respond to you in a constructive, respectful way. ..cliff mass

  18. jimijr has it right:

    "Climate is what you expect. Weather is what you get."

    Ask any aviator.

  19. Plenty of line scientists disagree with you Cliff. https://www.scientificamerican.com/article/scientists-see-climate-change-in-californias-wildfires/

  20. Bruce Kay, now your cult demands that the media preach your doctrine. The only difference between you people and the medieval Catholic Church is that you don't yet have the power you seek.

  21. Earthwater... very poor article and the "scientists" said very little. Can you tell me where I got the science wrong. Can you tell me one error I have made?..cliff mass

  22. Don't fret Place Slipper. You're still my favourite but I must say, Jim is kinda cute

  23. In my opinion, your statement that "global warming can't be to blame" is overly strong. Keep in mind that absence of evidence is not evidence of absence, and to me it seems like, at most, you've tried to demonstrate the former. At most one could conclude is that "global warming may not be to blame". Also, I don't agree with some of the items you mentioned, such as "Climate models do not suggest massive increases of rainfall over northern California under global warming". Well, the National Climate Assessment (NCA4) would seem to disagree somewhat with that:
    which shows their climate model resulting in greater winter rainfall and lesser summer rainfall; while that does not mean "massive increases in rainfall," it does line up with what happened in California this past winter and this summer. And I don't think it is too subtle to see the increased fire risk in wetter winters and drier summers.
    Another point worth emphasizing, which is a statistical subtlety that I think is often lost in climate discussions, is that small changes to the mean of a statistical distribution can result in much larger changes in the frequency of extremes, a fact relevant to looking at extreme events like these fires. A seemingly small change in the expected rainfall, say 10%, could potentially result in a much higher increase in the rate of massive fires.
    The statistics of large-scale fires are further exaggerated by the critical nature of fires: below a critical density of combustibles, fires virtually cannot spread. Beyond that critical threshold, the expected scale of a fire rises dramatically.
    I'm not saying that "for sure global warming caused the fire," but rather the subtle details of climate change could have contributed. Now they very well may have lowered the risk of fires somewhere else; it's very possible. But to conclude that climate change had no effect seems like over-stepping to me.

  24. Time was when your cult's priests would piously intone that weather and climate are different. Now your cult has erased any distinction, and then calls anyone who notices a heretic ... er, "denialist."

  25. So it is over-population and poor agro practices, along with human error in electrical infrastructure and poor urban and suburban planning. These do all tend to lead to an impacts on the environment that create a perfect vortex for the conditions that may cause those wind and temperature conversions.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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