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《Acta Geographica Sinica》 1979-03
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Zhang Peiyuan Gong Gaofa (Institute of Geography, Aeademia Sinica)  
3. Based on evidences from Chinese historical documents, the number of severe winters per decade is accounted. During last 400 years, not only the cold years, but also the tracks of cold air masses, were arranged into groups. According to modern studies, there are three main tracks of cold air masses in China, namely, the east, the middle and the west, they are divided approximately by the longitudes 105癊 and 110癇. The historical analysis in this paper shows that, during the warm periods, the cold air masses would have the east track rather than the other two, while during the cold periods, the cold air masses would have the middle and west tracks rather than the east one. The above-mentioned facts imply that, during historical time, the Westerlies did not undergo much changes in the warm periods, and the East Asia Trough was more variable and deepenend as well as situated more westward in the cold periods. 2. In historical documents, many hazards of frosts which killed the grain-crops were recorded. Prom these data, the isotimic lines of first and last date of frosts during 1400-1900 A. D. were drawn. It slwws that the frost season were almost 10-30 days longer than today, and that the higher the latitude, the larger the amplitude. 3. During recent 500 years, the flood hazards were more frequent before 1700 A. D., and less so afterwards. It is particularly evident in the Chang Jiang and Huai He River valley and southward. Viewing the South-East China as a whole, the droughts and floods have been increasing since the 20th century, and have approached its climax during past 500 years. 4. Finally, this paper discusses the effects of climatic fluctuation on agriculture during historical time. Based on more than one hundred reports dispached by gover-nors of various provinces to the emperors, maps of the date of reaping wheat in China during 1736-1759 are drown. It is found that it was about 10 days later than today. The southern limit of severe frost hazard for growing mandarin trees during past 500 years is discussed also, it was about 3-6?Lat. southwards than today.
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