The years-long study also looked at how climate change is impacting the timing of the bloom each year.

University of Washington (UW) scientists are in the final stages of publishing research that better predicts the timing of the campus’ cherry blossom bloom, an iconic sight in Seattle. 

UW PhD candidate Autumn Maust took over the research project in 2020 but said it started years prior. She said student data collection started in 2018 and the tree’s bloom timing was tracked beginning in 2012. Plus, researchers collected media from newspaper clippings and photos dating back to the 1960s to analyze the bloom timing. 

The final research is currently in review and should be published in the spring.

“There are two goals for this research project,” Maust said. “One is to be able to predict with a certain degree of certainty when bloom will occur. The second was to determine if there are any detectable shifts in when the bloom was occurring historically dating back from 1966 to present. So are we seeing any changes in that bloom time through that 60-year time period?”

Those two goals have been accomplished. 

First, the team finalized a metric to predict the timing of the bloom. They figured out the “degree days” that need to accrue for the trees to reach bloom. 

The magic “degree days” number for UW’s cherry trees in the quad is 170. This is similar to a piggy bank: the more you put in, the sooner you’ll get to the final number. The warmer it is, the sooner 170 is reached. 

“The warmer the climate is, the more degree days will accrue," Maust said. "And similarly, if it’s a bit colder, we’ll accrue less and it will delay those transitions through the bloom phases."

The team estimates that 4-6 degree days are added to the total every time a day with lows in the 40s and highs in the 50s occurs. They use the 10-day forecast to look at the weather coming in the next week and a half and calculate the expected timing based on that. 

The second part of the final research looks back on how the timing of the bloom has changed in recent decades. 

Scientists analyzed records dating back to the 1960s to record when the bloom started. Based on historical data, they determined the bloom is delayed an additional two days per decade, resulting in the bloom hitting a week and a half later than it did in the mid-60s. 

Scientists attributed this to the warming climate. The trees need cold during the winter and then warmth just before the bloom. With warming winters, that necessary cold is not panning out. 

“As the climate continues to get warmer in the Pacific Northwest, the warming part is not a problem,” Maust said. “It’s reaching the warming units that the trees need at an accelerated pace than they have historically. However, because our winters are so mild in the Pacific Northwest, they are also getting warmer. So it’s becoming harder for those trees to accrue the chilling units that they need.”

The bloom this year is expected later than expected because of wet and cold weather. In early March, Maust guessed the bloom might arrive around March 20. But with rain and cold weather continuing through the middle of the month, she estimates the bloom will begin around March 26. 

Bloom typically lasts between two to three weeks, depending on the weather. Once the bloom begins, cooler temperatures and no precipitation will prolong the timing of the bloom. 

Article from: https://www.ktvb.com/article/tech/science/environment/environment-northwest/uw-tool-predict-cherry-blossom-bloom-timing/281-b30e24b7-2839-4f6a-a692-04fe2620c96c