Japan: New Steward Appointed For 1,200 Years of Cherry Blossom Data
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The Japanese take their cherry blossom very seriously and have been compiling data on it since 812 C.E.
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 over a millennia of cherry blossom history, one of the longest-running records of the shifting seasons, when he died of cancer in 2025.
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. He learned to read ancient Japanese script in order to do this.
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, told the New York Times. “I want to carry this forward for as long as I can.”
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.
Mankai (full bloom) typically occurs in late March to early April in Japan's major cities, including Tokyo, Kyoto, and Osaka, lasting about one week before petals fall. Earlier blooms occur in southern regions (March), while northern areas like Hokkaido bloom in late April/early May.
