Study On The Spatio-temporal Process Of Oasisization And Desertification In The Period Of The Mingqing Dynasties And Republic Of China In The Middle Reaches Of Heihe River

The ecological environment is extremely fragile in arid areas, and the major epicontinental process of arid areas is oasisization and desertification. Under the influence of the increasing human activity and the change of global climate, the oasisization is blocked seriously and the desertification developed evidently. In order to understand the causes of these problems deeply, it is necessary to research the spatio-temporal process of oasisization and desertification and its impact on human activities. The study of oasisization and desertification process in historical period, which is beneficial for understanding the impact of human activities in a long scale, is significant for understanding the modern process and trends of oasisization and desertification.In this paper, the research methods, such as Historical Geography, Remote Sensing (RS) and Geography Information System (GIS), were used comprehensively to study the oasis and desertification process during Ming, Qing Dynasties and Republic of China (R.O.C) in the middle reaches of Heihe River. Based on remote sensing image, the area and range of the ancient oasis had been rebuilt quantificationally, and the spatio-temporal process of oasisization and desertification had been also analyzed. The results showed that:1. In the early Ming Dynasty, the study area had been developed on a large scale, and the ranges of oasis were expanded rapidly, then, reduced gradually in the next decades and recovered from Jiajing to Wanli.2. During the Qing Dynasty, oasisization and desertification were developed alternately:in the early and late Qing Dynasty, due to the influence of the war, a massive desertification had been caused in the reaches of Heihe River. In the Mid-Qing Dynasty, due to the massive development of oasis, the range of oasis expanded rapidly and was much more than the range of Ming Dynasty. The oasis in Jinta was also developed massively at this period.3. During R.O.C, the oasis was developed incessantly on the basis of Qing Dynasty. Under the impetus of the advanced science and technology, the range of oasis was expanded rapidly. However, these did not lead to a massive desertification due to the duration of the shrink of oasis in the early R.O.C is very short,4. The oasis distributed dispersedly in the whole reaches of Heihe River, at the same time, most of them concentrated in coastal areas of the Heihe River and Beidahe River. Due to the impact of the desert, gobi and mountains, the area of oasis were very small in the north/east of Heihe River. The expansion of the oasis area were occurred mainly in the area south/west of the Heihe River. 5. The overall change tendency of the area of oasis was increasing gradually over the study period. In the six parts of study period, the oasis range of ROC is the largest one, followed by the Mid-Qing Dynasty, and that of the early Qing Dynasty is the smallest one. The massive oasisization took place in the period of the early Ming Dynasty, Mid-Qing Dynasty and R.O.C, and the desertification took place in the period of the early and late Qing Dynasty.6. The main human factors which included the political and military situation, land development policies and population, had affected the oasis change. The expansion and contraction of oasis were largely determined by the political and military situation. When the social situation was stable, the policies of land development affect directly the change of oasis. In addition, the population was also an important restrictive factor.