Jennifer Borresen,Dinah Voyles PulverUSA TODAY
Clouds of delicate cherry blossoms unfurl across the National Mall in Washington D.C. each year when weather conditions send a cue to the trees, but under the influence of a warming climate, the stunning spectacle arrives earlier than it used to.
This year the blooms peaked on March 17, the National Park Service announced Sunday. That's the second earliest date since Japan gifted cherry trees to the people of the United States more than a century ago. The earliest was March 15, 1990.
The earlier blooms illustrate the influence climate change is having across the nation, from earlier springs and longer summers to warmer winters and more intense heat waves and extreme rainfall.
It's the first time that peak bloom – when 70% of the blossoms on the Yoshino cherry trees are open – occurred before the start of the National Cherry Blossom Festival since the festival’s start date was moved about a week forward in 2012. The festival started Wednesday and continues through April 14.
Historically the cherry blossom festival often started in early to mid-April. Over time, the festival length was extended and the start date moved forward. The festival hasn’t started in April since 1994.
Average daily maximum high temperatures in the District of Columbia are rising about three-tenths of a degree per decade, according to the National Centers for Environmental Information. The 20-year average overnight low temperature has increased almost a full degree since 2000.
The trend in warmer temperatures helps prompt the cherry trees in the nation's capitol and many other flowering trees to bloom earlier, said Theresa Crimmins, director of the USA National Phenology Network, based at the University of Arizona.
An earlier start to spring flowers
Though individual blossom dates still vary from year to year, trends in warmer spring temperatures, both the daily highs and the overnight lows, is seen in locations and around the world.
Last year in the United States, spring started early in the South and that trend rolled all the way up the East Coast, Crimmins said.
This year, spring’s arrival was average in the south, but it was “the earliest start to spring,” dating back to at least 1981, in a belt stretching from northern Kansas, across portions of Iowa, Nebraska, Illinois, Indiana, Ohio and a bit of southeastern Michigan, Crimmins said.
Cherry trees need a certain amount of cold days in the winter, followed by enough warm days to trigger flowering, said Elizabeth Wolkovich, a professor in the forest and conservation sciences at the University of British Columbia, who oversees a contest where citizens worldwide can predict peak bloom dates in D.C., Kyoto and three other cities. Cherry blossom seasons have advanced as much as two to three weeks in some locations, Wolkovich said.
The peak cherry blossom also arrives earlier in Japan, breaking records that date back to 801, according to researchers with the Met Office Hadley Centre in the United Kingdom and the Osaka Metropolitan University in Japan. The season arrives 1-2 weeks earlier than it once did because of human-caused climate change, the researchers said.
Climate change also has affected springs in Europe.
Wolkovich recently discussed with a colleague the juxtaposition of these earlier springs.
"I find spring brings feelings of the end of winter and start of growth, rebirth and many hopeful things," she said, "but with the springs getting so earlier, it's a mixed emotion as these earlier springs are correlated also with heat waves, bigger wildfires and sea level rise."
Rising sea levels threaten the trees
Warmer temperatures aren't the only impacts of climate change along the mall. Rising sea levels are compounding problems with crumbling seawalls along the Tidal Basin that have settled as much as several feet since they were built in the late 1800s and early 1900s, the park service said on March 13.
Water flows over the sea walls twice a day, even during normal tidal conditions, the park service said. Even greater flooding occurs during astronomical high tides and storms.
To fortify the walls and prepare for higher water levels in the Potomac River, the park service will begin a three-year, $113 million project later this spring that includes the removal of 140 cherry trees between the Thomas Jefferson Memorial and the Franklin Delano Roosevelt Memorial, and another 160 trees, the park service said on March 13. When complete, the plans call for the replanting of 455 trees, including 274 cherry trees.
