SOME CHARACTERISTIC FEATURES OF CHINESE CLIMATE AND THEIR EFFECTS ON CROP PRODUCTION
1964, 30 (1):
In China, from the time immemorial, climate has always been considered as capable of exerting an inordinate influence on the production of agricultural crops. Among the various climatic factors, total amount of insol ,lion, temperature and rainfall are deemed to be the most important. 1 .Total arnozcnt o f insolation Basing on the data obtained at 26 solar radiation stations by- direct observation at earth's surface in various parts of China during the period 1957-1960, and 136 other points calculated by interpolation, maps of annual and monthly total radiation, as well as annual and monthly radiation balance of whole China were drawn by Mr. T. K. Zuo etal, of Institute of Geography, Academia Sinica, in terms of kilogram calories per square centimeter per minute (for annual distribution of total solar radiation see Fig. 1). In the annual chart, the striking thing appears to be the fact that the lines of equal insolation do not go parallell with the latitudes, but in the eastern part of the country, they form in concentric circles with the Red basin of Sze-chuan province as the nadir point, with 90 kilogram calories, and the amount increases outward, more rapidly toward W. and less so toward E. This is largely due to the increasing cloudiness toward that province, owing to the SE. monsoon and the mountainous topography. Another interesting feature is the fact that in North China the annual insolation increases landward due to the de- crease of cloudiness and the increase of altitude. Maximum insolation occurs in Southern Tibet, but even in Northern Sinkiang the amount of annual insolation still exceeds any place south of the Yangtze River. The distribution of total radiation explains at least partly, why- the yield of paddy rice in Tientsin district is 30% or so higher than that of Shanghai district per unit area, and why the record of highest yield of spring wheat, over 500 kilogram per mu (1/6 of an acre) is held by the agricultural experimental sta- tion at Delinha, about 240 kilometers W. of lake Kukunor, at the altitude of about 2500 meters.Compared with the chart of annual total radiation of the whole world as construc-ted by Dr. M. E. Bydiko, Director of the Central Geophysical observatory at Lenin-grad, USSR, it is obvious that besides the Sahara, Arabia, and Mediterranean regions, Tibet and N}}V. China, including Sinkiang and Tsaidam Basin, rank very high in the amount of solar energy received every year among large land areas in the N. Hemi-sphere. Even in E. China the amount of solar energy received annually exceeds that of Japan or W. Europe where the rice and wheat crops give the highest yield per unit area in the world.2. Temperature The lowland of E. China, where most of the grain crops are produced in the country, is located in monsoon region. The monsoon climate distinguishes itself by firstly, a regime of maximum summer rainfall and a long dry season in winter; and secondly, by its excessive heat in summer and inordinate cold climate in winter, compared with re-gions on the same latitude. Thus monsoon climate is extremely favorable for the grow-ing of paddy rice, which gives very high yield per unit area when compared with other grain crops such as wheat, barley or rye. It is, therefore, not an incidental fact that 90% of the rice crop in the world in the past were produced in SE. Asia where mon-soon climate prevails. According to meticulous investigations made by Japanese meteorologists on the cor-relation coefficients between different climatic factors, such as duration of sunshine, tem-perature and rainfall on the one hand, and amount of yield of rice crops on the other,it was apparent that temperature exerted an outstanding influence on the rice harvest in Japan, especially the monthly mean temperature for July and August. The higher the temperature for July and August, the higher the rice yield. This is true not only in Hokkaida in N. Japan, but also valid in Kyoto districts in Honshu. Whenever the mean monthly for July and August falls below 20癈 in Hokkaido or 22癈 in central Honshu, the failure of rice crop invariably follows. It should be noted that climatically China is more continental than Japan, which means, that among places along the same latitude, stations in China have higher mean monthly temperature in summer and a lower mean monthly in winter than those in Japan. In grain crop production it is the summer temperature that counts. Hence, other thins being equal, so far as summer temperature is concerned, China has a more favor-able climate for rice production. Since China's liberation in 1949, the cultivation of paddy rice has been already eatcnded m beyond latitude 50癗 in Agun region along the Amur River.3. Rainfall Agriculturally speaking, monsoon climate has another advantage in that the rainfall concentrates in summer months, when the farm crops needs the moisture the most. It enables the monsoon regions to grow summer cereals on steppe without irrigation, while elsewhere irrigation is a necessary measure to insure a good grain harvest on the tem- perate grassland. On the other hand, the farmers of monsoon region is greatly handicapped by a long dry season in winter, and especially, by the great variability of annual and monthly amount of rainfall. Famines due to droughts and floods in India and ancient China are quite frequent. Fig. 2 depicts the mean annual rainfall variability of China proper and NE. provinces as constructed by Prof. P. H. Chu of the Department of Mereoro-logy, Nanking University, Nanking. It shows that the whole of N. China as well as regions along the sea-board, have a mean annual rainfall variability of 20% or more. Of course, the monthly mean rainfall variability in spring and early summer for N. China is still much greater, it attains as high a value as 45--70%.As a point of reference, it may be mentioned that in Great Britain no-where the mean annual rainfall variability approaches 16%;and in New York State of U.S.A., it gets to only 9%.In this con-nection it may be of interest to mention that in S. Australia the average wheat yield is very low due also to the unreliable rainfall amount as pointed out by the English Geo-grapher, Prof. L. D. Stamp in his book "Land for Tomorrow". Having made a rough assessment of assets and liabilities of climate in China, it behooves us to utilize the favorable climate resources as much as we can, and to miti-gate and combat its sinister aspects by measures made available by modern science and technology. With these facts in view nine points are proposed, to be applied to different parts of China according to the climate and general geography of the region.
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