T HE term Chinese-Tibetan borderland as used here refers to the region between approximately 95? and 105? E. and 28? and 33? N. (Fig. I). It embraces the valleys of the Min, Yalung, and Kinsha Rivers and the headwaters of the Lantsang. Lying between the Red (Szechwan) Basin, which has an average elevation of 500 meters, and the lofty Tibetan plateau, more than 5000 meters above sea level, it is a region of complex and rugged relief. High mountains tower above deep gorges trending generally north-south. In general, the elevation is more than I5oo meters. In such rugged country there is of course a considerable diversity of climate and scenery; dry steppes in the valley bottoms form a striking contrast with the luxuriant primeval forests of the mountain slopes. Despite the distance from the Pacific, the region lies within the reign of the southeast monsoon that surges in from the South China Sea in summer.' Pilot-balloon soundings have revealed that the summer monsoon in West China usually reaches a height of more than 500s meters and hence easily spreads over eastern Tibet without obstruction. The lofty border ranges of the plateau, however, force the monsoon to deposit its moisture on their windward slopes and act as a continuous rain screen. Precipitation decreases abruptly westward. On the eastern slopes of the ranges the normal annual precipitation is about 2000 millimeters; to the west the annual means are rarely more than 600 millimeters. In Sikang the yearly averages range from about 700 millimeters in the southeast to less than 5oo millimeters in the northwest, undoubtedly a natural result of the direction of the prevailing moisture-bearing winds and the northwestward increase in elevation. Because of the mountain barrier in the southeast, the upper Min Valley
Search from 250 M+ research papersSearch from 250 M+ research papers
Jan 1, 1986
A Lu 