Japan feels the heat as temperatures set to soar again this summer

Temperatures across much of Japan soared to unseasonably high levels over the weekend, with the country's meteorological agency warning of another scorching summer.

As extreme weather becomes more frequent, environmental experts say hotter and drier conditions threaten a range of sectors, from agriculture to fishing, with knock-on effects for human health and worsening habitat destruction.

"Japan has a rapidly ageing population, and it is this sector of society that will be hardest hit by high temperatures and humidity," said Rajib Shaw, a professor at Keio University's graduate school of media and governance who specialises in climate change adaptation.

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"To already see 27 degrees (80.6 degrees Fahrenheit) in April is very worrying, and there will certainly be an impact on human health."

Thermometers in central Tokyo touched a high of 26.1 degrees Celsius on Saturday afternoon, a temperature typically not seen in the city until mid-June. Several other cities across Japan similarly recorded unusually warm conditions for the time of year, with Sano in Tochigi prefecture, just north of Tokyo, the hottest at 27.9 degrees.

The Japan Meteorological Agency has blamed the elevated temperatures on a high-pressure system moving over the main island of Honshu, with Isesaki in Gunma prefecture, central Japan, reporting a maximum temperature of 27.1 degrees and the city of Funabashi, east of Tokyo, experiencing 26.6 degrees. It will be even hotter over the summer, the agency said.

In late July last year, the agency issued a nationwide warning of "once-in-a-decade temperatures", with spot temperatures nudging 40 degrees (104 degrees Fahrenheit). The daytime temperature for July in Japan typically averages around 30 degrees (86 degrees Fahrenheit) and 23 degrees (73.4 degrees Fahrenheit) at night, but both figures have been climbing in recent years.

Record highs were reported last summer in all but four of the nation's 47 prefectures, with the heatwave linked to the El Nino phenomenon affecting ocean temperatures and weather systems in the Pacific.

This summer is on course to match those withering temperatures. In its predictions for the April-to-June quarter, the Japan Meteorological Agency said there was a 60 per cent likelihood of the southern two-thirds of the nation experiencing above-normal temperatures, with the Tohoku region of northern Japan and Hokkaido having a 50 per cent likelihood of elevated temperatures.

It's a similar picture in the June-August period, with the possibility of higher-than-average temperatures increasing to 70 per cent in the islands of the Okinawa archipelago.

In a separate report, the agency said the surface temperature of the ocean surrounding Japan reached a record high between June and February for the third consecutive year. Ocean monitors in Sendai Bay, northeast Japan, recorded a surface temperature of 13.5 degrees (56.3 degrees Fahrenheit) in mid-March, 4 degrees (7.2 degrees Fahrenheit) higher than at the same point in 2023 and 6.3 degrees (11.3 degrees Fahrenheit) above the average.

"Sea surface temperatures were already high in the western Pacific and this is one of the main reasons why temperatures across Japan are already high this year," said Yoshihiro Iijima, a climatology professor at Tokyo Metropolitan University.

"Rising sea temperatures are a long-term trend linked to changes in the Black Current that flows up the east coast of Japan."

The Kuroshio (Black Current) is a warm ocean current that typically curves east into the Pacific after reaching the Boso peninsula, to the east of Tokyo. Since the spring of 2023, however, it has continued flowing north off the coast of the Tohoku region, bringing warmer weather and species of fish more commonly found in southern Japan.

The shift has been exacerbated by global warming trends and changes in the circulatory system in the Pacific, Iijima said, with significant implications for future weather patterns.

"The current coming this close to the coast is likely to intensify annual temperatures and, combined with global warming, means that we can expect to see the development of more and more powerful anticyclone weather systems over Japan and East Asia," he said.

In addition to the dangers to Japan's elderly population, higher temperatures could also harm agriculture and fishing industries and exacerbate natural disasters, Keio University's Shaw said.

"Erratic climate patterns will also have a direct impact on the agriculture sector, with consistently hot and dry days affecting rice production, fracturing the grains and reducing both the quality and size of the yield," Shaw added.

Seasonal fruits - a crucial part of Japan's rural economy, which is already under pressure - would also be affected, he said, with reduced crops of sought-after grapes, strawberries, apples and other high-end fruits.

Shaw said rising sea temperatures could cause fish to move to new areas further away from Japan's coasts, resulting in trawlers staying at sea longer and spending more on fuel, which could cause fish prices to rise.

The higher possibility of natural disasters linked to climate change is another serious concern, he said.

More frequent and powerful storm systems threaten to dump greater amounts of rain over the country, leading to flooding. In low-lying coastal areas, there is a greater risk of sea defences being breached as well as major landslides in mountainous areas, he said.

This article originally appeared on the South China Morning Post (SCMP).

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