Changing temperatures put peak dates for cherry blossoms into question

By Greta Easthom

For the third year in a row, a warmer-than-average January and February has accelerated the arrival of Washington, D.C.’s annual cherry blossoms, according to the Washington Post’s Capital Weather Gang.

When 70 percent of the cherry blossoms along the Tidal Basin have fully grown, Capital Weather Gang considers this to be peak bloom. The average date for peak bloom, historically, was April 5. Within the past century, that date has changed to March 31.

Cherry blossoms have bloomed especially early in the past two years. The National Park Service’s most recent projection for this year is March 27 through 31.  

“This year is tricky to predict because [the growth] started so soon, but slowed way down,” Samenow said. “The pattern will start getting warmer next week, so that will start to move things along.”

Cherry blossom
The cherry blossoms on the National Mall have begun to bloom early this year.

The National Cherry Blossom Festival spans from March 20 to April 15, perhaps to account for this uncertainty. Samenow said the Capital Weather Gang has been successfully predicting the flowers blooming for the past six to seven years, using a combination of peak bloom records, climate data and weather forecasting models.

“The development of cherry blossoms — and many other flowers too — is closely linked to temperature,” said Dr. David Inouye, professor emeritus in UMD’s biology department.  “One way scientists measure that is by calculating ‘degree days,’ which depends on how warm it is each day, above some threshold value.”  

Inouye said the forecast in the past month may have led to a “false spring,” which occurs when a “warm spell triggers flowering earlier than usual.”

“One consequence of the increased frequency of false springs…is that this sets up the potential for a late frost to kill the buds or flowers,” Inouye said. “This has happened in the past to the D.C. cherry blossoms, and it now sometimes has major consequences for agriculture worldwide.”

According to Inouye, tree rings can detect the effects of a late frost, as the growth ring will be narrower than usual.

“If there is a late frost that kills buds or leaves, that may affect the resources they are able to accumulate this year, which may influence how much they grow or how many flowers they make the next year,” Inouye said. “There will be some adaptation as plants and animals respond to climate change, and evolution will proceed in response too. But if people prefer the way things were in the ‘good old days,’ then it will take some major social responses.”  

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