In a country which, across about 30 ° of latitude, extends from the tropic almost to the rigid zone, it is natural that the climate presents differences, sometimes considerable, in the various regions. The predominant factor in the Japanese climate is the monsoon regime. During the cold season, the anticyclonic area that forms, due to the lowering of the temperature, in northern China and eastern Siberia, gives rise to a current of cold air (the so-called winter monsoon, which blows from October to April) which invests its own Japan and Formosa from the north-east and the Ryū-kyū from the north. Its violence is such that it is sometimes necessary to suspend the ferry-boat service in the Strait of Korea. In western Japan, beaten by the monsoon, cloudy skies predominate and snowfalls are abundant, while in the Ryū-kyū and Formosa, located further south, there is almost daily rain. In eastern Japan, on the other hand, protected by the mountains, good weather prevails, especially in November, December and January. In the NE provinces, however, due to the fact that the central chains are not very high, the monsoon crosses the country until it reaches the Pacific; this means that the region from Aomori to Sendai and Kōriyama is also covered with snow throughout the winter.
During the hot season, the strong sunshine causes a rise in temperature in Mongolia and northern China; at the same time, the anticyclone of the northern Pacific is expanding almost to the Japanese coasts: the result is a current of hot air (the summer monsoon, which blows from May to September) which invests Japan itself and the Ryū-kyū from the south and Formosa from SO. Its influence on the state of the weather in the archipelago is minimal and therefore no appreciable climatic difference occurs on either side. The weather is generally nice, except for the summer rainy season (June-July). These rains, called by the natives bai – u or tsuyu “plum rains”, because they coincide with the ripening of this fruit, are due to a succession of cyclonic areas that slowly move from the neighborhood of Formosa and northern China towards Kyushu and Hondo. Typhoons, a very frequent phenomenon in Japanese climates, originate in the vicinity of the Caroline, Marshall and Marianne islands, from which, advancing towards the west, they incline more and more to the north, until they reach the seas that bathe the Japanese coasts, causing infinite damage to crops, inhabited areas and ships. Mostly they appear in July-September, once every 7 or 10 days.
For temperature, the main factor is, of course, latitude. However, especially in the north, due to the influence of the monsoons, the winters are more rigid than the latitude would entail. In Asahigawa, for example, in the center of Yezo, on January 25, 1902, the thermometer dropped to −41 °. In Hondo, in general, it is less cold, although it is not uncommon to reach zero and sometimes, especially in the center and north, it falls below. In the Ryū-kyū and Formosa, located in the semitropical area, the average winter temperature is 15 ° in the north of the former, and 20 ° in the south of the latter. In summer, latitude has little influence on temperature. During the day this is almost the same in the north and in the Ryū-kyū. After sunset, however, the heat decreases rapidly in Hondo and Yezo, while it still lasts for several hours of the night in the south, especially in Formosa. In the provinces bathed by the Inland Sea, temperatures are generally not very high and in the evening the air is calm, often muggy.
According to Ezinesports, the transition from winter to summer is very short in the north and in the center, where the snow begins in November and lasts until mid-April; in June you can already feel the summer heat, which lasts until mid-September. October is the most pleasant month almost everywhere. Frost is common in early November. In the south, the change of seasons is gradual and autumn and spring have a relatively long duration. Excessive humidity is a feature of Japan’s climate and makes it one of the most rainfall-rich countries in the world. In summer it causes sultry days, so painful to bear for the foreigner and also, albeit to a lesser extent, for the native. The following table contains the most important climatic data:
Hydrography. – Due to the limited extension of the main islands of the Empire and the very pronounced relief of them, the rivers of Japan generally have a short course and torrential character, often presenting rapids of artistic effect. From these conditions of things derive an advantage and a disadvantage for the country’s economy: an advantage in that the rivers offer generally favorable conditions for hydro-electric exploitation (the availability of water power has been calculated at approximately 8 million HP, of which about 2 million, equal to 25%, used up to now); a disadvantage in that their navigability is hampered and the country has limited river traffic. It is still interesting to note that the rivers flowing into the Pacific have, in general, faster course than those that flow into the Sea of Japan, which instead have greater length of the path. The following data is for Japan’s main rivers.
In the islands of Kyūshū, Sakhalin and Formosa, no river exceeds 200 km. of length.
As for the lakes, the territory of the Empire has many and of various origins, but all, with the exception of Lake Biwa, have a very limited extension. In general, the deepest are of a tectonic or volcanic nature. The following table brings together the data on the most important ones.