CHINA - CLIMATE China has the essential monsoonal characteristic of a seasonal reversal of wind and a corresponding sharply marked seasonal differentiation of rainfall. The northerly outflowing winds of winter give its dry season, the southerly inflowing winds of sum mer its season of rains. Unlike India, hemmed in by the Himalayas, China is open to Central Asia by way of Mongolia from which strong and very cold winds sweep down in winter. So, too, in summer, China, unlike India, is not the single ob jective of the air circulation of a whole ocean and its monsoon consequently yields a less heavy and less concentrated rainfall spread much more equally over the interior. China, moreover, is a warm temperate rather than a tropical land, only its extreme southern fringes lying to the south of Cancer.
The winter monsoon sweeps over China from the north-west, but southwards it becomes first northerly in the Yang-tze delta and then, combining with winds blowing off the sea, north-easterly along the south China coast. North China experiences the north westerly and the south China coast the north-easterly regime during the whole winter monsoon (September to March). The intermediate Yangtze delta is affected by the land-winds only from October to February ; in September and again in March the prevailing winds are north-easterly from off the China seas. Be tween the winter and the summer monsoon comes a transitional period of calms (April and May) with light southerly breezes. The true south-east monsoon, never as strong as the north-west monsoon of winter, blows from June until August and, sweeping in from the sea, gives all China the bulk of its rainfall and also a striking uniformity of temperature, in strong contrast to the great regional variation in winter. Only locally, as in the Formosa channel, does the wind drift become south-west.
Exposed to the full blast of the north-westerlies from Central Asia, north China experiences exceptionally severe winters, the coldest in the world for its latitude (on the basis of temperatures reduced to sea-level). On latitude N., Peking has an average January temperature of 23.5° F, St. Louis of 31.o F and Naples of 46.8° F. The whole of China north of the Hwai river has at least one month whose mean temperature is below freezing-point. The Yangtze valley is warmer, with temperatures in the depth of winter more like those of Britain, although the winter itself is much shorter. Yet the lake expanses of Tung-ting and Po-yang in the Yangtze valley, in flood after the summer rains, are at times frozen over. South China has definitely warm winters, those of Hongkong being as warm as an English midsummer, although snow has been known in Canton. The winter, even in north China, is comparatively short and spring is nowhere long delayed. Summer uniformity is such that the midsummer tem perature of Peking approaches to within 3° F of that of Hongkong (July 81.7°). The high temperatures are, however, much less prolonged in the north. It is agriculturally important that south China has temperatures of over 6o° F practically throughout the year, the Yangtze for six to seven months, and north China for five months. The Yangtze valley has a "temperate" climate with neither the extremes of north China nor the uniformly high tem peratures of the south, and this feature is most pronounced in the sheltered Red basin of Szechwan which, although far in the interior, has milder winters and cooler summers than the valley below the Gorges. (See SZECHWAN.) South-east China, ridged more or less at right angles to the monsoonal current, receives as a whole (the Fukien coast excepted) a higher annual rainfall— about 6o in.—than the plateaux of south-west China and the basin of Szechwan far in the interior, with about 4o inches. The average rainfall for the basins of the lower Yangtze is slightly higher. The summer rainfall of southern China seems to be evenly dis tributed, save for exceptional precipitation on the southern coastal strip. High relief in south-west China counter-balances its interior situation, and so promotes this relative uniformity. North China, on the other hand, has a comparatively low relief and is a greater distance from the source of moisture. Hence while the Yangtze delta has about 45 in., the plain to the north of the Hwai river receives from 20 to 3o and the loess plateau of north-west China less than 20 ; the rains die away altogether as the Gobi desert is approached.
Taking China as a whole, the rainfall is heaviest in the season of the south-east monsoon and least at the height of the north west monsoon in mid-winter. Peking, as typical of north China, receives 75% of its precipitation during the summer months. But only 4i% of the total fall of Shanghai occurs in that season. The Yangtze Valley in winter receives occasional cyclones which draw in air from the south and from the sea on their southern flanks. These southerly winds temporarily replace the winter monsoon and bring rain. On the hilly coastlands of Chekiang and Fukien further precipitation occurs from condensation of moisture brought by the north-east monsoon. Thus the Yangtze valley and the coastal provinces of the south-east have a more evenly distributed rainfall than any other part of China. (For climatic regions see below, Natural Divisions of China.)