The climate in Japan

Japan is an island nation in East Asia that has a very diverse climate due to its geographic location and topography. The country stretches over 3,000 kilometers from north to south, encompassing a range of climatic zones from the subtropical Okinawa Islands in the south to the snow-capped mountains of Hokkaido in the north.

In general, Japan has four distinct seasons, with hot summers and cold winters. The country is influenced by seasonal winds and ocean currents that bring hot and humid air in summer and cold and dry air in winter.

In the northern part of Japan, which includes the island of Hokkaido and the Tohoku region, the climate is predominantly cold and snowy. Long, severe winters with temperatures below freezing prevail here. Often there are heavy snowfalls. Summers, on the other hand, are cool and mild, with average temperatures around 20 °C.

In central Japan (Kanto and Chubu), the climate is milder and more temperate. Summers are hot and humid and temperatures often reach 30°C or more, while winters are relatively mild with only occasional snowfall.

In southern Japan, which includes the Kansai, Chugoku and Kyushu regions, the climate is subtropical and more influenced by ocean currents. Summers are hot and humid, with temperatures regularly rising above 35 °C. Accordingly, winters are also rather warm and mild at 10 °C.

The Okinawa Islands, located in the very south of Japan, have a tropical climate with warm temperatures all year round. The islands have a rainy season from May to June, followed by hot and humid summers and mild winters.

Temperature records of the last 150 years

The hottest temperature measured from 1873 to January 2023 was reported by the Nagoya weather station. In August 2018, the record temperature of 40.3 °C was reported here. The hottest summer from July to September, based on all 62 weather stations in Japan below 610 meters altitude, was recorded in 2010 with an average temperature of 25.7 °C. This average temperature will normally be measured every four to six hours, thus also including the nights. Normally, this value is 23.7 degrees Celsius. The average maximum daily temperature at that time was 29.6 °C.

The coldest day in these 150 years was reported by the Asahikawa weather station. Here the temperature dropped to -25.7 °C in January 2008. Asahikawa lies at an altitude of 140 meters above sea level. The coldest winter (January to March) was in 1875 with an average temperature of -0.7 °C. In Japan, it is usual to have about 5.8 degrees more at 5.1 °C for this three-month period.

The most precipitation fell in August 2014. With 50.4 mm per day, the Kochi weather station recorded the highest monthly average of the last 150 years. Incidentally, the region with the most rainfall for the whole year is around Owase. The driest region is near Abashiri.

Long-term development of temperatures from 1923 - 2022

In contrast to single record values, long-term development cannot simply be brought about by all weather stations in the country. Both the number and the locations are constantly changing. An average value would give a distorted result. If several measuring stations in particularly cold mountain or coastal regions are added in one year, the average would decrease as a result of this alone. If a station fails during the summer or winter months, it does not provide any values and distorts the average again. The subsequent long-term development was therefore reduced to only 24 measuring points in order to have comparable data over as long a period as possible.

In the years 1923 to 2022, there were only these 24 weather stations in the whole country, which reported continuous temperature values. From these weather reports, we have created a long-term development that shows the monthly average temperatures. The hottest month in this entire period was August 2010 at 27.1 °C. January 1945 was the coldest month with an average temperature of -0.4 °C.

The average annual temperature was about 12.6 °C in the years after 1923 and about 14.8 °C in the last years before 2022. So in less than 100 years, it has increased by about 2.2 °C. This trend only applies to the selected 24 weather stations in Japan. A considerably more comprehensive evaluation of global warming has been provided separately.

Data basis and methodology

The data from the individual measuring stations are based on the archives of the German Weather Service, individual values averaged and supplemented by own elements. In order to determine a representative national average, average values were first calculated for each part of the country, which were then summarized at the national level. Thus, if a disproportionate number of weather stations are located in a small area, their number does not affect the national average.