TOKYO – Japan’s four distinct seasons that have inspired its rich bounty of traditions, food and culture are threatened by global warming, potentially jeopardising livelihoods in areas from tourism to agriculture to fisheries.

One expert has even warned that the nation is on track to become “a country of two seasons” – summer and winter – with blink-and-miss-it periods for spring and autumn.

The bleak prophecy came after Japan faced a prolonged muggy summer in 2023.

In Tokyo, there were a record 143 “summer days”, defined as when temperatures rise above 25 deg C, spanning the equivalent of nearly five months.

The last such day was on Nov 7, when the mercury soared to 27.5 deg C in the city in a new high for the month, with mosquitoes still uncharacteristically active.

Yet the temperature plunged dramatically in a matter of weeks. By Nov 26, it was a wintry 5 deg C in Tokyo.

The late and abrupt change in temperatures has an indelible impact on the arrival of Japan’s vivid symphony of reds and yellows. In Sapporo, peak autumn foliage season arrived on Nov 13, more than two weeks later than usual.

In Hiroshima’s Miyajima, which is now in peak maple viewing season, the local authorities have tried to manage expectations of far more resplendent views. “While it is now the best time to view maple leaves, many trees this year have shed leaves without reaching their full colouration,” they said.

Such is the case, anecdotally, in autumn foliage hot spots across the country from Kyoto to Kanazawa to Karuizawa, as well as in the highlands of Tochigi and Nagano.

Mr Hiroki Ito, a weather forecaster at Japan Meteorological Corporation, which provides autumn foliage and sakura, or cherry blossom, forecasts, told The Straits Times that the peak autumn foliage has appeared later than average in 2023, given the abnormal weather patterns.

Maple leaves turn colour when the green pigment chlorophyll, used in photosynthesis, gradually breaks down as the temperature dips below 20 deg C. The colour deepens as the red pigment anthocyanin is synthesised below 10 deg C.

It is too early to foresee any immediate impact on tourism, beyond illumination events having to be scheduled and tourists having to factor in the delays.

But Mr Ito warned that it is possible for the New Year to be heralded with autumn foliage: “If summer becomes even longer in future, the best time to see autumn leaves will be delayed even further.”

In 2023, Tokyo is expected to reach peak autumn foliage on Dec 1, which is three days later than average. In the 1950s, such foliage appeared in the city between Nov 8 and 15.

Over in the Nasu Highlands in Tochigi, north of Tokyo, the peak autumn season was forecast on Oct 22. But most leaves were still green at that time.

“Usually it gets pretty cold after September, so the leaves will turn red, but that’s not the case this year,” managing director Shuichi Sakai of Cafe Madoka, which has a terrace offering scenic views, told TV Asahi.

“There was no autumn, and winter seems to have come all of a sudden.”

The country is also set for a warm winter with lower-than-average snowfall in 2023, according to a forecast by the Japan Meteorological Agency on Nov 21.

But it did not discount the chances of sudden blizzards that would dump powder snow. Simulations show that the warmer-than-usual waters around Japan may evaporate and condense into snow clouds in a cold front, resulting in heavy snowfall.

These warmer waters, along with the hotter summer, have hurt Japan’s agriculture and fishery industries. Catches of autumn seafood like salmon and Pacific saury have drastically fallen. For example, the haul of Pacific saury in Choshi city, Chiba prefecture, reportedly stood at zero in 2022, the first time since the 1950s when record keeping started.

At the same time, the quality of produce such as rice and sweet potatoes has been affected.

According to prefecture-level data, Niigata, Japan’s top rice cultivation region, suffered damages amounting to 13.5 billion yen (S$121 million) in 2023 – equivalent to 13 per cent of revenues in a conventional year – due to a lower rice yield and poorer-quality grains resulting in lower prices.

Over in Ibaraki’s Namegata, the nation’s top producer of sweet potatoes, local cooperative chief Yuji Kuriyama told ST there have been a few – but concerning – number of cases where the insides of sweet potatoes were found to be blackened.

“We won’t know until the sweet potato is cut open by the customer,” he said, adding that the produce do not look any different on the surface. “The affected sweet potatoes are also edible, but they do not taste as good and may damage our brand. It is random, and so I’m having a really hard time.”

These unpredictable weather patterns have meant a need to adapt. Farmers and fishermen are now experimenting with weather-resistant crops and aquaculture.

On the tourism front, events on the cultural calendar are being shifted. Some fireworks festivals, the quintessential Japanese summer experience, which are traditionally held in August, have been moved to October when evenings are comparatively cooler.

This was the case for Ibaraki’s Tsuchiura All Japan Fireworks Competition and Tokyo’s Tamagawa Fireworks Festival. The latter’s organiser reportedly said: “This was to avoid the ‘abnormal summer heat’ that has become more severe in recent years.”

Warmer temperatures in recent years have also meant that spring is arriving earlier in Japan, when the fiscal and academic years begin in April by design to coincide with the blooming sakura flowers to signal a fresh start.

The sakura now blooms in mid- to late March instead in Tokyo.

Mr Ito told ST: “Both the cold of autumn and winter and the warmth of early spring are necessary for cherry blossoms to bloom.”

The dormant flower buds are awakened by the cold weather, and then bloom as the temperature warms, he added, noting that the biorhythm would suggest that the sakura would bloom sooner in areas that warm up faster from winter.

Mie University meteorologist Yoshihiro Tachibana told TBS News: “Japan is a country where you can really enjoy the seasons, with cherry blossoms in spring and autumn leaves in fall.”

“But that may soon cease to be the case as extreme weather becomes the norm. Soon, Japan may become a country with only two seasons.”