Beth Chen had been tracking the status of the Tidal Basin cherry trees for weeks before her visit on a drizzly March 25. While monitoring the status of the blooms on the website BloomCam, she figured the trees would reach peak bloom in April, too late for her friend, Maureen Sharon, to see them on her visit to Washington, D.C. But a warm February sped up the flowers’ development. This was followed by a cold March that slowed the blossoms down, leading to peak bloom on March 23, according to the National Park Service.
“The weather is extremely unusual,” Chen said. “But it was a tremendous benefit because I had a friend visiting who, peak blooms were on her bucket list, so it worked out perfectly.”
Trying to predict the cherry blossom bloom is a popular guessing game around Washington, D.C. The Washington Post, NBC Washington and the National Park Service all take a stab at guessing the correct date. It’s no easy task and, according to Matthew Morrison, arborist and urban forester at the Park Service, forecasting peak bloom has become even more challenging in recent years.
Morrison oversees 20,000 trees at the National Mall and Memorial Parks, including 3,700 cherry trees. He’s also part of the group attempting to predict peak bloom yearly. His team had been using Growing Degree Days, a measure of heat accumulation. But recently, that model started coming up short.
“That was fairly effective. Maybe they’d be 60% effective or something along that line,” Morrison said. “But now, it seems to be with the environmental changes, that model seems to be kind of failing us.”
Morrison has incorporated other data, like solar radiation, to help improve the Park Service’s predictions. But he’s noticed other changes in the trees’ blooms due to climate change, including areas of the trees’ flowers developing at different rates.
“Today, I was out looking at the cherry trees and one tree might have portions that are in full flat wood, other portions where the flowers are still developing. And that’s on one tree, and that’s very, very unusual,” Morrison said.
The flowers aren’t the only part of the trees that have been impacted by climate change, according to Morrison. Rising tidal waters have introduced pollution and heavy metals into the soil where the cherry trees grow. Hotter temperatures have made the trees more likely to get sunscald on their bark, which Morrison likens to sunburn.
It takes a year-round effort to combat these changes and keep the trees healthy. The Park Service puts down woodchips to help replenish the soil and has started pruning fewer branches to keep the trees’ canopies intact to better protect their bark from the sun. They also monitor the trees for diseases, which can decimate stands where every tree is the same species, like the cherry trees at the Tidal Basin.
“So that leaves us in an area that requires a terrific amount of maintenance and monitoring and worrying,” Morrison said. “So the urban forester has sleepless nights worrying about the stand of either 3,700 cherry trees or the remaining of the 20,000 trees in general.”
Despite all of these challenges, the cherry trees’ pink blooms remain beautiful, even on the rainy day when Beth Chen and her friend Maureen Sharon set out for a stroll around the Tidal Basin.
“I think they’re beautiful,” Sharon said. “I wish it was sunny just for pictures, but it’s kind of nice to not have the crowd.”