How does Japan predict its cherry blossom forecast?

What goes into predicting one of the biggest annual celebrations in Japan? Source: Shutterstock.

MARCH is certainly one of the most wonderful times of the year for Japan.

It marks the coming of spring after the harsh cold winter and also the long-awaited sakura (cherry blossom) season.

One of the biggest annual celebrations in Japan, the pink phenomenon is the result of dozens of different cherry blossom varieties blooming together. Rows upon rows of cherry trees are awash with perfect blooms, creating a soft and romantic atmosphere for lovers and friends.

In Japanese culture, this is when hanami (enjoying the transient beauty of flowers) is practiced, through outdoor picnics or parties beneath the cherry trees during daytime or at night.

This is why the cherry blossom forecast, usually announced every year by the country’s weather bureau, is important. The estimated viewing dates are based on data collected in previous years, especially the latest years 2016 and 2017.

The blossoms usually take a week to reach full bloom once flowering has begun and that full bloom also lasts around a week. Because the blossoms only last a week or two, the forecast is watched closely by those planning hanami.

Source: Shutterstock/Paul Davidson

Accurately predicting Japan’s springtime magic is important for travelers as it allows for proper planning of your journey so you will not miss the beautiful pastel-colored splendor.

“People pay more attention to the cherry blossom season than any other flower in Japan,” Japan Meteorological Agency official Ryo Dojo told AFP.

So what is the most basic element of predicting when the seasonal spectacle will unfurl? For starters, a large data set of temperatures. According to Dojo, the flowers will come earlier if the temperatures rise quickly in spring.

On the flip side, if the autumn and winter seasons in Japan suddenly see temperatures which are higher than usual, the cherry blossom blooms can end up making an appearance later than usual.

To add on, extreme weather can also affect the cherry blossom trees, with unusual patterns in 2018 prompting some blossoms to appear well before the usual season.

In October 2018, cherry blossoms unexpectedly bloomed due to the year’s unusual weather, including a particularly active typhoon season (July to October). The series of unusually warm days after typhoons confused the plants into flowering.

Source: Shutterstock.

That having said, generally, the cherry blossom blooms are expected to begin as early as March in southern Kyushu and appear as late as May in northernmost Hokkaido.

These forecast findings are strengthened by Weathernews’ crowdsourcing data, which relies on photos of buds sent in regularly by 10,000 citizens across the country who are registered on the company’s website and app.

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

In 2004, Weathernews launched the “sakura project,” signing up members who choose their own cherry tree and send pictures of its buds to the firm at regular intervals.

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

To date, the project has accumulated data from two million reports on cherry flower buds, which its used 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 around 700 parks regularly to check the growth of cherry flower buds. The company and other forecasters also employ mathematical models and algorithms.