Tue, Feb 12, 2019 - Page 6 News List

The art and science of Japan’s cherry blossom forecast


As spring approaches in Japan, the country’s weather forecasters face one of their biggest missions of the year: predicting exactly when the famed cherry blossoms are to bloom.

Japan’s sakura, or cherry blossom, season is feverishly anticipated by locals and visitors alike. Many tourists plan their entire trips around the blooms, and Japanese flock to parks in the millions to enjoy the seasonal spectacle.

“People pay more attention to the cherry blossom season than any other flower in Japan,” said Ryo Dojo, an official of the statistics unit at the Japan Meteorological Agency.

The most basic element of predicting when the delicate pink and white petals would begin to unfurl is a large data set of temperatures.

That is because the flowers will come earlier if temperatures rise quickly in spring, Dojo said.

Conversely, if temperatures in the autumn and winter period are higher than usual, the blooms can end up being delayed.

Extreme weather can affect the trees too, with unusual patterns last year prompting some blossoms to appear in October, well before the usual season.

In general, blooms begin as early as March in southern Kyushu and appear as late as May in northernmost Hokkaido.

In a bid to improve its forecasts, some outfits have started crowdsourcing data, including Weathernews, a company in Chiba, which is near Tokyo.

It relies on photographs of buds sent in regularly by 10,000 citizens from across the country who are registered on the company’s Web site and app.

“Cherry blossom forecasting is impossible for us without this system,” spokeswoman Miku Toma said.

The company launched what they call the Sakura Project in 2004, signing up members who choose their own cherry tree and send pictures of its buds to the firm at regular intervals.

“We realized that we could see the details of how buds grow thanks to the pictures sent to us, so we decided to incorporate the project to help predict blossoms,” Toma said.

Just observing the bud can give surprisingly accurate information about how far the flower is from full bloom.

A sakura bud still a month from blossoming will be small and firm, but after 10 days, the tip turns slightly yellow-green and then a darker green part emerges.

When the tip of the bud turns a faint pink, bloom-time is just a week away.

Thanks to the project, Weathernews has accumulated data from 2 million reports on cherry flower buds over the past 15 years, which it uses to increase the accuracy of its forecasting.

It also incorporates weather data collected from its own observation devices across Japan — 13,000 locations in total, 10 times more than the official weather agency has. Weathernews employees also call about 700 parks regularly to check the growth of cherry flower buds.

The company and other forecasters also employ mathematical models and algorithms.

Otenki Japan, a forecaster run by a subsidiary of precision-equipment manufacturer Shimadzu, even began using artificial intelligence to predict last year’s cherry blossoms.

The forecasts are not only for flower fans, but reflect the fact that sakura season is big business in Japan.

Cherry blossoms symbolize the fragility of life in Japanese culture, as full blooms only last about a week before the petals start falling off trees.

In that period and the preceding weeks, shops pack their shelves with sakura-themed merchandise.

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