The secret to Japan’s precise forecast of the dates when cherry blossoms bloom

Hanami in Tokyo, Japan.
Hanami in Tokyo, Japan.
Image: Reuters/Kim Kyung-Hoon
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Each spring, Japan celebrates the season of cherry blossoms, or “sakura.” Viewing parties and picnics underneath the pale-pink trees are a national pastime, recognizing the fact that beauty and life are fleeting and that a new season has begun.

The excitement around sakura is not just philosophically sound, however. The flower is also an economic powerhouse. “Sakura season is big business,” as The Japan Times puts it.

In the weeks before the flowers bloom and the parties start, shops display countless themed items, from cherry-blossom beer to flower-flavored chips and other goods perfect for picnicking in the spring. Last year, stores sold cherry blossom Pepsi, for example. And tourists come to the country in droves hoping to enjoy this uniquely Japanese tradition.

That makes predicting exactly when the blooms will appear very serious work. In 1951, Japanese meteorologists began trying to get ahead of the blooms for better planning. Today, the “sakura zensen,” or cherry blossom front, is a closely-monitored affair that’s reported nationally as spring approaches. The reports draw on observations from national weather agencies, algorithms, park managers—and 10,000 citizen scientists.

In 2004, the Chiba-based company Weathernews, Inc. began enlisting the assistance of citizens, who register on the company website and app to be official blossom monitors. Now, there are 10,000 individuals who each sign up to watch a local cherry blossom tree carefully all year and regularly report on the state of its buds, sending in photos for meteorologists to study. Miku Toma, a company spokesperson, tells The Japan Times, “Cherry blossom forecasting is impossible for us without this system.”

Predicting the blooms can be tricky because their arrival date depends on the weather year-round and in the winter weeks. Warmer temperatures generally mean blossoms appear earlier, while cold temperatures indicate a longer wait ahead. In the fall, for example, there was concern that extreme weather that prompted some trees to blossom unseasonably in autumn might mar this spring’s hanami, or sakura-viewing activities.

But now meteorologists believe this year’s sakura will be as splendid as ever. “[A]lthough cherry trees bloomed out of season last October due to a loss of leaves caused by wind and salt damage from a series of tropical cyclones affecting Japan in September, it is thought that the impact on this spring’s cherry blossoms will be minimal,” Weathernews announced on Feb. 5.

The company also laid out upcoming sakura spectacle dates across Japan. Blooms will be visible in Tokyo on March 18 through March 28. That gives city dwellers just 10 days to enjoy the canopy of pastels that will emerge. ”Nationally, it looks as though the blossoms will be slightly later than last year, when they appeared earlier than usual,” the company reports.

In Hokkaido, up north, the first flowers are expected to emerge on April 27, just ahead of Golden Week, which begins on April 29 and is a week-long celebration of national holidays. For the intrepid blossom-watcher who’s willing to travel around the country in pursuit of fleeting beauty, that means all of spring will be one big party.