The cherry blossom as an indicator of climate change

A cherry blossom is a flower of numerous trees of genus Prunus. They are also known as sakura. They usually refer to decorative, not edible cherry trees.

Wild species of the cherry tree are generally spread in the northern hemisphere. In Japan, cherries are grown for ornamental purposes, and it is recognized the national flower of Japan.

Every year the Japanese Meteorological Agency and the public track the cherry blossom front as it runs northward up the Japanese archipelago with the arrival of warmth via regular forecasts accompanying the weather part of a newscast TV.  

The blossoming starts in Okinawa in January and commonly reaches Tokyo and Kyoto at the end of March or April. It continues into northern territories, arriving in Hokkaido several weeks later. Japanese careful attention to these forecasts and turn out in large numbers at parks and top cherry blossom places for and picnicking under the trees and taking photos. The pastime of cherry blossom seeing even gets its word in Japanese - "hanami."

Reddit user JoshOlDorr made in python using phenology data a chart that shows the beginning of cherry blossoms in Tokyo over a time interval of more than 1,000 years.

Cherry blossom

On the chart below, the brown line is a 100-year rolling mean. The dotted line indicates the lowest centennial mean value before 1850, which dipped down in the mid-1900s. 

According to Osaka University's phenology data, the 2021 blossom season in Tokyo and Kyoto climaxed 26 March.

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