In Japan, a New Steward for 1,200 Years of Cherry Blossom Data Has Been Found, Sustaining a Climate Change Research Project

Climate scientist Yasuyuki Aono, who died last summer, learned to read ancient Japanese script to compile records on peak bloom dating back to the ninth century C.E.

Christian Thorsberg | Daily Correspondent

April 23, 2026

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The death of a beloved scientist left empty an idiosyncratic but important post in Japanese scholarship. Climate scientist Yasuyuki Aono was the steward of a database of 1,200 years of cherry blossom history, one of the longest-running records of the shifting seasons, when he died of cancer in 2025.

Fans of his efforts searched for someone new to take up the mantle. Just as Japan’s 2026 cherry blossom season waned, a replacement record keeper was named.

Genki Katata, an environmental biophysicist based in Tokyo, will assume the venerated role of tracking and forecasting the much-anticipated pops of pink and white that welcome spring in the ancient capital Kyoto.

“Making sure the Kyoto data lives on is a very important job,” Katata, who works at the Canon Institute for Global Studies, tells the New York Times’ Hiroko Tabuchi. “I want to carry this forward for as long as I can.”

The peak bloom period of the annual cherry blossom season, known as mankai in Japanese, occurs when 80 percent of the flowers of a given variety have opened. The Japanese Meteorological Agency measures it for Yoshino cherry trees, and the benchmark doubles as the unofficial start of spring.

Aono kept track of mankai for the Yamazakura cherry trees in Kyoto, using historical records to compile calendars that date back to 812 C.E.

“I have searched and collected the phenological data for full flowering date of cherry tree (Prunus jamasakura) from many diaries and chronicles written by emperors, aristocrats, governors and monks at Kyoto in historical time,” Aono wrote of his process, BBC News reported in 2021.

He taught himself to read ancient Japanese script to access old texts that suggested when flowering likely occurred in any given year. Like this one, per the Times, about a celebration near the Kyoto Imperial Palace: “We enjoyed watching cherry blossoms, and took sake provided by the emperor,” wrote Tokitsune Hiramatsu, a court noble and scholar, in a diary entry on April 14, 1644.

Aono’s body of work is both a cultural and a scientific achievement. Researchers around the world have used his cherry blossom records to study how climate change has shifted seasons in Japan.

“In Kyoto, records of the timing of celebrations of cherry blossom festivals going back to the ninth century reconstruct the past climate and demonstrate the local increase in temperature associated with global warming and urbanization,” climate researchers wrote in a 2009 paper published in the journal Biological Conservation, citing Aono’s data.

Just last week, as a testament to this warming trend, the Japanese Meteorological Agency announced a new word—kokushobi—to describe “brutally hot” days exceeding 40 degrees Celsius (104 degrees Fahrenheit), reports BBC Weather’s Mallory Moench.

Aono’s journals show that he tracked cherry blossoms in his final months.

“You can very much see that he planned to continue,” Tuna Acisu, a data scientist at Our World in Data, an online platform that publishes a chart based on Aono’s data, tells Chris Baraniuk at the Guardian. In Aono’s records, charts he planned to fill in 2026 sat empty. “That made me a little bit emotional,” Acisu says.

Katata says he plans to continue Aono’s research, tracking how climate variability, urbanization and warming affect Kyoto’s cherished trees.

“There aren’t many people like Aono-san,” Katata tells Baraniuk in the author’s newsletter, The Reengineer. “We really need to do that [kind of work]—to understand the current climate.”

Christian Thorsberg | Read More

Christian Thorsberg is an environmental writer and photographer from Chicago. His work, which often centers on freshwater issues, climate change and subsistence, has appeared in Circle of Blue, Sierra magazine, Discover magazine and Alaska Sporting Journal.