THE CLIMATIC TYPES OF FLOODS AND DROUGHTS IN THE VALLEYS OF THE YANGTZE AND THE HUAI RIVERS
C.LEE AND M.W.WAN Institute of Geophysics and Meteorology,Academia Sinica
On the basis of the past climatic records in China, World Weather Records and various climatic data published in Japan, this paper in an analysis deals with the flood and drought types in the valleys of the Yangtze and the Huai Rivers from the standpoint of climatic conditions. Four comparatively outstanding types have been discovered in the valleys, viz. flood and drought types, each of which is divided into two kinds. The two kinds of the flood types are: (1) the trough type and (2) the obstructed low type. The trough type is the result of the existence of two highs in the Northwest Pacific, one in the south, being the Subtropical Pacific High and the other in the north, being the Okhotsk High. Lying between these two highs is a trough, and it is in this trough that flood used to occur. The obstructed low type gives rise to floods when the eastward low pressure systems in the mainland of China are checked from going on by the Subtropical Pacific High. The two drought types are: (1) the shrunken high type and (2) the advanced high type. The shrunken high type. ?In summer, the Subtropical Pacific High shrinks, ebbing away from the mainland, while only the Okhotsk High appears in the northeast part of the sea. Cold air currents usually go in a southerly direction from Siberia at this time, overwhelming the mainland of East Asia, hence the formation of a vast dry area in China and Japan and the suffering in the Yangtze and the Huai valleys from the dry weather. The advanced high type. ? When the Okhotsk High is comparatively weak or indistinguishable and the Siberian cold waves are not prevailing in summer, only the Subtropical Pacific High is rather developed and advancing towards the mainland of East Asia, which is almost fully covered by the warm air currents, hence the appearance of dry weather in the Yangtze and the Huai valleys in the meantime. In connection with this type, sometimes the wedge of the Pacific High extends westward to the neighborhood of China's southeast maritime region and sometimes it moves northward to the Okhotsk Sea. For this reason, this type may be again devided into two sorts: one with ihe wedge of the high going westward and another going northward.