UW's Cherry Blossom Timing and Our Winter Weather

One of the singular events each year in Seattle is the stunning display of white/pink blossoms on the Arts Quad at the University of Washington.  At maximum bloom, the flowering is simply stunning.

Interestingly enough, there is quite a bit of variation of the date of peak bloom, the day when the crescendo of color reaches its apex.   A day that I have told follows the beginning of blossoming by about one week.

As shown below, since 2012 the peak bloom dates have varied from mid March through early April.  Talking to some cherry blossom experts today, it appears that this year's peak bloom should be on March 31, give or take a day (and I have plotted it). 

I have done some recreational reading about this important topic, including a very nice paper by Chung et al. that finds that Cherry blossom timing for the famous Washington DC blooms is closely related to winter and early spring temperatures.  Colder winters delay flowering.  And they used some of the UW blossoming data as well.

So can we explain the above variation in blossom date with local temperature variations?  And do the above variations suggest the influence of global warming?

Let me begin by plotting December through February temperatures for the Puget Sound lowlands from the NOAA Climate Division Data. 

The two warmest years were 2015 and 2016 and YES, they had the earliest peak bloom.  Very good.  2017 was the coldest year and its bloom was quite late (well into April).  But 2018 was late, but the temperatures were not exceptionally cold.  In short, there is clearly some kind of correlation, but it isn't perfect.  In fact, the Chung et al paper suggests this, revealing that to get flowering requires sufficient cold early in the season and a certain amount of heating late in the spring.  So the relationship is a bit more complex

One thing is sure, the short period shown above (2012-2019) does not suggest a progressive earlier flowering as would be expected with warming.   And certainly the winter temperatures plot does not suggest a warming trend....if anything temperatures have cooled this decade, with a warm spike in 2015.  But this is simply too short a period to have much confidence in any trends.

I am trying to acquire a longer term blossom date data base to secure a better estimate of a longer-term trend.  Will do another blog on this topic if I get it.  If anyone can help me get it, let me know.