It’s impossible to walk across campus without seeing them: dozens of pink cherry blossom trees in full, glorious bloom. Across Washington, DC, the cherry blossoms are budding, most famously down at the Tidal Basin where they attract hundreds of thousands of visitors.

According to the National Park Service, peak bloom will arrive on the early side again this year. The peak date is defined as the day when “70 percent of the Yoshino Cherry (Prunus x yedoensis) blossoms are open.” Traditionally, this day has occurred between the last week of March and the first week of April, though temperature variations have resulted in peak anytime from March 15 in 1990 to April 18 in 1958.

Anecdotally, it seems that these famous blooms arrive earlier and earlier each year, and many people wonder if global warming is involved. We turned to AU Assistant Professor of Environmental Science Michael Alonzo to weigh in on our question of the week:

Is Cherry Blossom Season Really Getting Earlier and Earlier Each Year, and Is Climate Change to Blame?

It does feel like spring comes earlier than it used to in DC, and this is true if the arrival of spring is considered to be when trees and flowers start blooming. 

In DC, we monitor tree phenology (the timing of plant life cycle events) more closely than most places because of our collective obsession with the cherry blossom trees, particularly those Yoshinos and Kwanzans surrounding the Tidal Basin. The timing of peak bloom is tracked closely (for over 100 years!) because it is the basis for determining the dates of the National Cherry Blossom Festival.

It is indeed the case that in recent years, the cherry blossoms have generally reached peak bloom stage earlier than in the past. There has been about a seven-day advance in that date since 1921, though there is considerable year-to-year variation. 

We know that the climate is warming, and there is a consensus among scientists that this warming causes plants in temperate regions to bloom earlier and frequently also to drop leaves later. The connection between climate warming and phenology is complicated though, so we’re not entirely sure about what exactly drives the earlier bloom date. It could be the warm spring, it could be the insufficiently cold winter, or it could be some combination of the two.

About Professor Alonzo

Assistant Professor of Environmental Science Michael Alonzo uses satellite and drone imagery (plus other geospatial tools) to study forests and land cover change, mostly in urban or boreal domains. Current or recent projects involving urban trees include: 

• Urban trees and cooling. We have a bike-mounted air temperature sensor to assess the spatial variability in urban heat here in DC. We also use this data collected by cars in many other cities around the country to examine the relationship between tree canopy, paved surfaces, and heat. 

• Urban tree response to heat part I. We have assembled hundreds of high-resolution satellite images to monitor the timing of green-up in the spring and leaf loss in the fall for every tree in DC. These "phenological" measurements are a window into tree response to climate change. 

• Urban tree response to heat part II. We fly drones with thermal cameras over trees in urban areas to estimate tree transpiration during hot times of year and hot times of each day. Are trees changing their transpiration patterns in response to ever warmer conditions?