历史时期黄河中游环境变迁与下游水患问题的研究

地质研究表明鄂尔多斯高原沙漠在史前即已存在,史籍也记载北魏时期该地区有大沙漠,"人造沙漠"的论点不能成立。东汉以后游牧民族入迁,使该地区及陕北、陇东草原破坏加剧,所谓"改农归牧使森林草原植被得以恢复"的论点与事实不符。由于上述地区植被的严重破坏,土地沙漠化和水土流失加剧,北魏中期黄河下游决、溢水患频繁,灾情极重,所谓"长期安流"史实无据。

RESEARCH ON ENVIRONMENTAL CHANGES IN THE MIDDLE REACHES OF YELLOW RIVER AND FLOODS IN THE LOWER REACHES IN HISTORIC TIMES

Recent years, geologists have discovered large areas of paleo aeolian sand existed in shifting sand dune, semi fixed and fixed sandy lands in Ordos Plateau. These proved that the desert was formed in prehistoric times. More proofs were recorded by 《Wei-su》 (History of the Northern Wei Dynasty):the Northern Wei emperor inspected the west in a A. D. 417, and hunting in "Great Desert" where might be today's Hobq Desert or Mu Us Desert by it's geography place. So the research results either from geology or historic geography suggest that the desert in Ordos Plateau had been existed in the Northern Wei or even before that time; the view of "man made sandy desert" taking farming after the Tang Dynasty as reason is untenable. After the eastern Han Dynasty, the quickly increased husbandry put great pressure and damage on the natural grass land, resulting from northern nomadic people massively moved into the middle reaches area of the Yellow River. According to 《Wei-su》, when one fight occurred in the place same as today's northern Shaanxi and Ih Ju League, the winner got livestock from enemy more than 2.03×107 head, average 125.5 head per km 2, and this figure near the level in early 1980' (130.9 head per km 2). Because of long term overstocking and backward herding manner, the grass land degraded seriously; Also, because the Wei Dynasty, Jin Dynasty and Sixteen Kingdoms periods were in the second cold dry period of recent 2000 years in China, so it is impossible to recover the damaged vegetation. In historic times the natural vegetation was ruined seriously in the middle reaches of the Yellow River, and added with great desert on Ordos Plateau and dry climate, heavy rain and flood was frequent there, During 18 years from a A. D. 468 to a A. D. 485, there were 9 times flood, average one time every two years. These proved that the consideration of "long term quiet" in middle Yellow River area after the Easter Han Dynasty is untenable.