April 13, 2017

Record Breaking Precipitation in California: Is Global Warming to Blame?

This has been an extraordinarily wet year over the entire west coast of the U.S., with many locations approaching or exceeding all time record precipitation amounts for the water year (which starts October 1).  

The question is why?

A number of media outlets and environmental advocacy groups are claiming (or strongly suggesting) that the heavy rainfall this year and the preceding dry period over California are the result of human-caused global warming.

 Is human-induced global warming associated with increasing greenhouse gases really the cause?

I believe that the evidence and good sciences indicates that the answer is no--the nature of what happened this year does not reflect what we expect from global warming.  Let me provide you with the evidence.

The precipitation that has hit California this winter has been truly extraordinary. I mean crazy high.

Want proof? The State of California has an index of Northern Sierra Precipitation for the total amount starting October 1. Yesterday, we beat the all time record for entire water year, and there is 5.5 months left in the water year.  This is a startling record to break.

Here is the percentage of normal precipitation for the western U.S. for the water year so far.  Your eyes are not lying to you....much of norther Sierra and neighboring areas had over 200% of normal precipitation.

How much above normal does this mean in inches?  As shown in the figure below for the same period, we are talking over TWENTY inches more than normal from central CA to the Pacific Northwest.   Amazing.

So much precipitation that most of the reservoirs in California went from well below normal to full.  No one expected that.

Now some in the media and some "advocacy" groups have been suggesting or stating that the heavy this year is the result of or "consistent with" the effects of global warming.   But they are not providing a scientifically based conclusion.
(As an aside, this is an area in which I have done research and have published several papers in the peer-reviewed literature.)

There is a substantial literature on the impacts of global warming on West Coast precipitation.  A number make use of the output of global climate models forced by increasing greenhouse gases.

An excellent paper by Neelin et al., 2013 in the Journal of Climate presented the average change in precipitation for December through February from a 15-member ensemble of the latest (CMIP-5) climate models (see  below). This map shows the difference between the precipitation between the end of the 20th and 21st centuries if greenhouse gases increase rapidly (RCP 8.5).   Note that there is small increase over southern California and a modest increase (about .5-1 mm per day or around 1.75 to 3.5 inches) for the entire winter.  And keep in mind, this is the magnitude of the change by the end of the century, today, the impacts of global warming would be much, much less (perhaps a tenth of this).

Clearly, the precipitation enhancement this winter is hugely greater than expected from global warming.  These results also speak to the precipitation droughts of the past few years--this is NOT what climate models are suggesting will occur from global warming.  California will not be getting less precipitation as the planet warms (although Mexico will get drier)

Climate models do suggest that the largest atmospheric rivers will get much more intense--my work with Dr. Mike Warner in published work in the Journal of Geophysical Research suggests that the strongest atmospheric rivers will be enhanced by 30-40%.   But that is not what what observed this winter; although we had a few strong atmospheric rivers, none were exceptional, something that is supported by the lack of major flooding events along the West Coast.

Instead of mega atmospheric rivers, West Coast precipitation was characterized by a seemingly unending number of modest events.  This is made evident by the precipitation record at San Francisco below (dark green is actual precipitation and light green is normal).

Seattle-Tacoma Airport experienced the same thing.  Here is the plot of daily rainfall (red color) and the daily records (green lines).  Rain nearly every day, but very few events reached daily records.  Not what you would expect from a global warming signal.

Furthermore, the origin of the persistent precipitation is no mystery--it was due to a very persistent and anomalous upper atmospheric circulation pattern.

To illustrate, here is upper atmospheric (500 hPa, around 18,000 ft) anomaly (difference from normal) of 500 hPa heights (you can think of it like pressure) for the last 90 days.  Huge anomaly, with unusually low pressure over the Northwest and offshore waters, a big ridge (high pressure) over the eastern U.S. and the southern NE Pacific, and other large anomalies offshore.

A low off our coast and a ridge to our south brings moist southwesterly flow and lots of precipitation over the West Coast.  This pattern may well have been forced by unusual convection (thunderstorms) over the Indonesian and environs.
There is no reason to expect this kind of pattern is caused by global warming, since the climate models do not produce this configuration when they are forced by increasing greenhouse gases.

Not convinced yet?   If global warming caused by steadily increasing greenhouse gases was the cause of the recent drought or this year's mega precipitation, you would expect to see a trend in California precipitation.  As you can see below (a plot of Oct-March precipitation over CA from the Western Region Climate Center), there is very little trend (I would not look before 1940 since there was far fewer stations then).   California has a lot of natural variability of precipitation with a few dry years followed by a very wet year or two.  But there is no real trend.  Global warming would produce a trend.

In summary, examining the California precipitation variability from a number of directions leads to the same, consistent conclusion:  there is no scientific evidence or reason to believe that recent variations in precipitation have anything to do with global warming.

For those that are interested, I will be giving a talk at Bellevue College next Tuesday (April 18th) on the politicization of climate science at 12:30 PM.  This is open to the public. And they have pizza.


How will Northwest Weather Change Under Global Warming?  Help Us Determine the Local Impacts of Climate Change

Society needs to know the regional impacts of climate change and several of us at the UW are trying to provide this information with state-of-the-art high resolution climate modeling.  With Federal funding unavailable, we are experimenting with a community funding to build this effort.  If you want more information or are interested in helping, please go here.  The full link is: https://uw.useed.net/projects/822/home    All contributions to the UW are tax deductible.


  1. In forestry, the most common modeling is growth and yield models. We need a tool to predict growth so that planning can be done based on logical known variables. The problem with these G&Y models is the same as the cause of this year's western precipitation... ANOMALIES!! anomalies, despised for their lack of tidiness, will, given enough time, blow our models out of the water (no pun intended). Example? The 96-97 ice storm took every growth and yield prediction for timber stands and put them through the shredder. Garbage in one day. Push the reset button. I love anomalies!

  2. Thanks for the interesting post Cliff. Have you read Michael Mann's latest nature article? https://www.nature.com/articles/srep45242
    He shows how climate change can lead to Rossby wave amplification and more extreme weather. I think what has happened in California recently is a perfect example of this. Persistent ridge for a few winters and drought then this winter persistent trough and floods. Even your California precip time series supports this since it looks like the standard deviation of annual precip has increased. Lots more research needs to be done here but I don't think you can rule out a climate change fingerprint

  3. "This pattern may well have been forced by unusual convection (thunderstorms) over the Indonesian and environs.
    There is no reason to expect this kind of pattern is caused by global warming, since the climate models do not produce this configuration when they are forced by increasing greenhouse gases."

    Any theories to explain the unusual convection over the Indonesian and environs? Or is just natural variability assumed?

  4. jdm83
    I looked at upper level wave amplitude...and found just the opposite....deamplification. My work is published in the peer-reviewed literature..cliff

  5. The fact that it's a record precip year but not a record snow year certainly could have something to do with global warming. Like all recent years, dry or wet, it's been warm, which is certainly consistent with what global warming would produce.

  6. Thanks for the insightful post.

    There appears to be a wide gulf between global warming and actual presumed climate change.
    Many attributed climate changes are actually contraindicated by GCMs.
    And as you point out here, the extent of modeled changes are small compared with the extent of observed fluctuations imposed by fluctuations of wave patterns.

    This does raise some points/questions:

    1. Which aspects of climate change due to enhanced greenhouse gasses are actually predictable?
    There are no control runs of actual climate so there's always argument of the 'counter-factual',
    but early work ( Manabe and Wetherald, 1979 and others ) noted that with increased CO2, we'd expect:

    * increased global mean temperature
    * cooling stratosphere (from the intense response)
    * large and out of phase Arctic warming ( from latent heat of freezing )
    * sub-polar upper tropospheric hot spot ( area of increased warming )
    * increased evaporation
    * increase in global mean water vapor
    * increase in water vapor transport to high latitudes with precipitation
    * decrease in snowfall
    * commensurate decrease in pole to equator SW gradient
    * commensurate decrease in temperature variability
    * commensurate decrease in kinetic energy associated with a weaker jet stream.
    * commensurate poleward migration of jet stream

    Observed, though not precluding natural variability are:
    increased global mean temperature, decreased stratospheric temperature, large and out of phase Arctic warming

    Contraindicated, at least for the satellite era: the hot spot

    Uncertain small signal or limited measurements: evaporation, water vapor, decreased snowfall, gradients, variability, jet stream changes

    The wave pattern for a year, as evidenced by the data above, is not predictable.

    Which things are predictable?

    2. I can hear Jenifer Francis and Michael Mann thinking out load about the persistent though moderate wave pattern you identify behind this past year's precipitation. This is predicated by a decreasingly intense merdional thermal gradient. In MW79, the authors identified such a decrease in gradient/jet/kinetic energy. But it also appears that this was based on a too intense decrease in high latitude snowfall compared with more recent 4xCO2 GCM runs:


    So perhaps a weaker jet stream is a plausible, but very small extent prediction.

    How does one verify/falsify the theory of the weaker,wavier,stagnant jet?

    The weaker jet theory is interesting to me because there's a big disagreement: Francis/Mann say weaker. Hansen says, no, high latitude oceans changes mean a stronger jet.
    Rossby's original considerations were before the RAOB era, so he proposed looking at surface temperature, which Francis invokes ( Arctic Amplification ). But the thermal wind of the jet is aloft, and indeed, if the Hot Spot were to occur, it would imply an increased gradient, apart from Hansen's oceanic arguments.

    It appears that there is disagreement about what's modeled, much less observed with respect to the general circulation and any associated changes.

    3. Your presentation sounds interesting - any chance of a recording and posting it here?

  7. Fantastic post, Cliff! I'm becoming a huge fan.

    Cliff Alexander

  8. Hi Cliff

    Any connection between the large El Niño of 2015-16 and last winter's precipitation?

    Looking back at the previous large El Niño in 1997-98 and Mt. Baker's record snowfall in 1998-99

    Curious what you think.

  9. This is part and parcel of why the GW crowd has yet to be taken seriously by everyone - it doesn't matter what happens with the weather each year, everything and anything is twisted, manipulated and crammed into yet more "proof" of severe climate change. Did you get more rain this year? Simple reason - GW. Did you experience a drought? Of course you did - because GW. How about more snow than usual? You got it - GW. It would help their cause if they admitted just once that their models are not infallible and that maybe - just maybe - they can be proven incorrect at times in their predictions.Humility is not their strong suit, and it's not helping their cause.

    1. Eric

      I understand your point and mostly agree. Your comment does overlook something very important, though. NORMAL weather, by definition the most common variety, is almost never associated with climate change.

      Cliff Alexander

  10. Timothy said: "The fact that it's a record precip year but not a record snow year certainly could have something to do with global warming. Like all recent years, dry or wet, it's been warm, which is certainly consistent with what global warming would produce."

    Where in the western US was it warm this winter? It was one of the harshest winters in a generation. Here is Cliff's post from 3/11: http://cliffmass.blogspot.com/2017/03/the-coldest-winter-in-generation-for.html

    It was the coldest winter since 1985 according to the NWS. Look at the map on that 3/11 post by Cliff. Exactly where in the western US was it "like all recent years, dry or wet, it's been warm".

    As for snow, here is an article from the Methow that calls the snowpack in the N. Cascades "unusually massive". http://methowvalleynews.com/2017/03/31/heavy-snows-will-delay-opening-of-n-cascades-highway/ The N. Cascades Pass may have it's latest opening of all time due to that fact. In some areas of our state we came very close to record snowfall, particularly in the N. Cascades. The snowpack remains >110% across almost all regions in the state. California is off the charts.

    Can you please back up your claim that "like all recent years, dry or wet, it's been warm"?

  11. A think an unequivocal “no” response to the question you pose at the start of the article is a bit on the strong side. While I’m not a climate expert, I have spent my entire career working with environment models of various sorts. My concern with ruling out climate change as being any part of this large increase in accumulated precipitation is two-fold: first, there are still uncertainties in our climate models, particularly when precipitation is involved; second, a large departure from what has been “normal” (or even beyond previous maxima) could be a manifestation of an unstable transition state of the atmosphere. The first point is somewhat self-explanatory, so I’ll focus on the second.

    At best, the climate models provide transitions from one state to another along what I would characterize as equilibrium states. As you are well aware, in a mathematically chaotic system such as our weather system, transition states can vary quite a bit from the equilibrium states as the system moves from one long-term equilibrium state (the past) to another (our future). That said, I don’t think that the fact that this past winter’s heavy precipitation load was way out of line with both the past and with climate models is necessarily a reason to state flatly that the event was not a side effect of climate change. However, it doesn’t necessariy mean that it was due to climate change, either. My criticism here is that I am not comfortable with your hard-and-fast “no” answer. I think it’s more of a “probably not, but it could be.”

    1. Seattle Jim

      It might turn out that there is a link between climate change and California's recent weather. Cliff's point is that right now there is no EVIDENCE for such a claim.

      Cliff Alexander

  12. Note that there is small increase over southern California and a modest increase (about .5-1 mm per day or around 1.75 to 3.5 inches) for the entire winter.

    Doesn't using this when talking about one year's weather violate the climate vs. weather rule? Yes, the average increase in precipitation will be small, but what about the variability? I thought that the climate models all predicted that there will be much greater swings in weather year-to-year with climate change? Drought one year, deluge the next. Oh, kind of like what has been happening in California...

    Frankly, it really feels like you are grasping for reasons to show that extreme weather is not caused by climate change with every one of these posts.

    1. How far back in time do you think you need to go to not find great "swings in weather year-to-year [caused by] climate change...like what has been happening in California"?

      Here is a graph to help you out:

  13. During our recent visit to Joshua Tree National Park, we encountered amazing flower displays thanks to the amount of rain they had this winter and spring.

  14. @sunsnow12 - This post is about California, not the Northwest. Oregon and Washington had a cold winter, but California did not, just like the rest of the country. If California had had a cold winter, obviously record precip would likely translate into record snow, which it has not.

  15. @sunsnow12 - "Snowpack in California’s mountains is also well above average and the highest since the very wet/snowy winter of 2010-2011. What is striking, however, is how much Sierra snow water equivalent has lagged overall precipitation. For example, Northern Sierra snow water equivalent is currently 145% of average (vs 202% of average for overall precipitation). This effect has been particularly pronounced at middle-elevation regions where wintertime temperatures are more “marginal” for frozen precipitation than at colder, higher elevations. While this winter has certainly been colder than recent (record warm) ones, conditions have still been near to above average across most of the state–and more importantly, have been considerably warmer than during most of California’s historically wet winters."


  16. Cliff - point taken. OTOH, here we go again with additional moving of the goalposts:


    Mann had to dramatically revise his infamous "hockey stick" chart after it was discovered that he had used incorrect and/or fraudulent data, now he's revising his predictions of another infamous "tipping point" to a later date. He's never wrong, it's just that his previous ironclad predictions were just off a bit. Second verse, same as the first.

    1. Eric

      Sounds to me like you've spent a lot of time at WUWT. If you disagree with Mann's opinions, just stick with Cliff Mass. He has a wealth of information and from what I've seen, his position's are always based on the best evidence.

      Cliff Alexander

  17. Perhaps, Cliff, you could explain to me as an astronomer why winters in the Pacific Northwest as of the last four years have been getting progressively worse. I have been a lifelong fan of yours for years, however as an astronomer who once had quite a lot of 'night sky time' in years past, I cannot believe you think that this cannot be because of global warming.

    As a Shelton-based astronomer and a lifelong weather geek, I am a little put off by this entry. This winter has been by far, the worst for astronomy. Last year wasn't much better. Ten years ago, I averaged 25 clear nights at the telescope from October 1st to April 1st.

    This year? I've had only three. All of those were in January. Last year? I had only four.

    I cannot fathom that climate change isn't somehow responsible for the worsening skies that astronomers in the PNW have dealt with over the last few years. As an astronomy club founder, I can't even plan a star party anymore.

    -Steve Rosenow
    (One frustrated astronomer in Shelton)

  18. Timothy said "Oregon and Washington had a cold winter, but California did not, just like the rest of the country. If California had had a cold winter, obviously record precip would likely translate into record snow, which it has not."

    Are you saying every location in CA had record precip? Because that is clearly not true. And there is nothing "obvious" about precip turning to snow -- it is far more complex than that -- but even so the snowfall in California has been massive, and that is supported by every data point and (non-ideological) article out there.

    There are plenty of areas that had record or near record snowfall - http://abc7.com/weather/california-snowpack-nears-record-depths/1779896/. Here is an LA Times two weeks ago stating "California Snowpack Is One of the Biggest Ever Reported" http://www.latimes.com/local/lanow/la-me-ln-sierra-nevada-snowpack-measurement-20170330-story.html

    And the reality is they are not done measuring it, and it will likely break all-time records in a number of locations.

    There is zero evidence 2017 has been "warm" in California, unless you want to hunt out specific areas (like the SE). In fact here is a map proving it: http://www.wrcc.dri.edu/cgi-bin/anomimage.pl?wrcJanTxdep.gif

    Particularly in areas where the vast majority of snow accumulates in the state, again... can you please provide evidence of it being "warm" this winter, and also data from the NWS backing that up?

  19. Cliff - I don't know what to make of Mann anymore, his research has been called into question so often that I find it amazing that anyone still cites him as an expert on climate. However, this technique of making up stuff and throwing it at the wall to see what sticks has infected much of the culture. Just look at the earlier comment on how an amateur astronomer's observations have led him to conclude that because he hasn't been able to see the stars very often during the winter, it must be because of GW.

  20. Eric...Well I am just reading another Mann etal article on a wave-guide theory of amplification of wave activity with global warming....very weak work. I am amazed it was even published..cliff

  21. @Sunsnow12

    This story from the Washington Post has a better graphic showing winter temps in California in that it covers departures from average for December to February. And also, since it has the entire contiguous U.S. is a reminder that the majority of the country did have a warmer winter.


  22. @sunsnow12 - No one said there isn't a lot of snow. There just isn't a corresponding record amount for the northern sierra, which would be a reasonable assumption if we had had a combination of cold year and record precip.

    Nov, Feb and March were well above average, Dec and Jan near average for California. The 5 month period Nov-Mar was a full two degrees above average. Above average = warm/not cold. https://www.ncdc.noaa.gov/temp-and-precip/climatological-rankings/index.php?periods%5B%5D=5&parameter=tavg&state=4&div=0&month=3&year=2017#ranks-form

  23. If someone wanted to make a documentary on climate change that would appeal to those who don't have much concern, they should find people from all over the Northern Hemisphere who have lived around an area long enough to witness the changes. Those "I used to raise reindeer, but now that the permafrost is melting, I'm digging up mammoth ivory" stories are something people can relate more to than the science. It's the farmers noticing changes who will convince others and the stories don't have to be that spectacular. The river that used to freeze and now doesn't is a good enough story. The farmer saying the growing season starts earlier or he can now plant crops that he previously couldn't plant is good enough. Stories requested by the OP are processed by the brain differently than scientific facts. People relate to other people's lives.

  24. http://files.opensnow.com/Tahoe/2017/snowgraph.jpg

    We just moved to Incline Village and are nervous about our first winter living here and are wondering what to expect. I looked at the graph found at the link above and am left bewildered. Can someone help me find the normal amount of snowfall we receive in the Sierra around Lake Tahoe?


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

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