The Desertification Of The Hexi Area In Historical Time

Desertification is one of severe ecological problems today. It directly reduced human survival space, decreased quality of life, threat to food security, it has done serious damage to human survival and development. In China, especially in the northern and western regions, after years of management, made a lot of achievements, But on the whole, still in a partial improvement in the overall deterioration of the situation; In certain areas such as the lower reaches of Shiyang River, the lower reaches of the Tarim River, still, there are severe desertification. Therefore the study of desertification and its related issues of national economic construction, social development and scientific progress is of great significance. Desertification in historical time as the basis and pioneer for the process of modern desertification and is the basis of the study of modern desertification and is one of the most important components. The Hexi area located in the northwest inland river basins with arid climate and the severe shortage of water resources, desertification problem is quite serious. Especially in the lower reaches of rivers, such as Minqin ,Ejin, Dunhuang, has become a serious obstacle to the local socio-economic development and to improving the people's standard of living; The problem of desertification in the region also have a direct impact on the ecological environment in areas around Beijing and Tianjin. In order to investigate the causes of desertification and mechanisms, to understand the historical roots of the problem of desertification, to provide historical reference China's northern and western regions of the ecological environment and socio-economic development. This paper studied the Hexi area, focusing on research and development of the region's history in the process and mechanisms of desertification period.The paper based on lots of fieldwork on 20 desertification areas in historical time in the Hexi area, NW China, especially on the investigation and study about 9 dry lakes areas and 72 typical abandoned ancient cities, recovered the complete situation of the desertification of historical time in the Hexi area, NW China used the methods of environmental archaeology, historical geography, and so on. It classified the type of desertification of historical time in the Hexi area, NW China to ancient oasis desertification of historical time and ancient lakes desertification of historical time. In spacial development pattern, the paper made further distinguish to the trace-source-development pattern and the swing-by-river-development pattern of ancient oasis desertification of historical time and the ring-shrink-and-outspread development pattern of ancient lakes desertification of historical time. And in time, the paper considered there were three main periods of desertification happened and expanded of historical time in the Hexi area, NW China; they were the South and North dynasties (A.D. 420-589), the Final Tang and the Five dynasties (A.D. 836-960) and the Ming and the Qing dynasties (A.D. 1368-1911) and corresponded to the main three cold periods in historical time; the degree of desertification was more and more severer and the areas of desertification was more and more.The paper indicated, in the Hexi area, NW China, there were two important postulates; firstly, there were widely sandy Quaternary sediment supplied material foundation; secondly, there were aridity climatic condition because of inland geographical position and the rise of Qinghai-Tibet plateau offered the climatic foundation. The macro process of desertification in the Hexi area, NW China was controlled mainly by the climatic changes in past 2000 years; the more severe degree of desertification was owing to the dry and cold trend in millenary scale since middle Holocene; the idiographic desertification processes in specifically periods in historical time was brought by the changes in temperature and humidity in centennial scale in historical time. But within the past 300 years human activities have played a primary role in desertification processes of the Hexi area, NW China.The paper reconstructed the intensity data of human activity during historical time, included the quantity of population, the population density, the area of plantation, the intensity of land-use and the rate of water resources utilization and so on; all data indicated there were unprecedented level of the intensity of human activity in middle of the Qing dynasty (middle to later of 18th century); especially the density of population in the middle of the Qing dynasty had exceeded the critical index of population pressure in arid land and the rate of water resources utilization had exceeded 40% indicated the impact of human activity to the desertification processes in the Hexi area, NW China had reached and exceeded the level of the impact of climate. The paper used the expressions on the impact of human activity, I=PAT, worked out the impact of human activity in historical time in the Hex area, NW China; it take the impact of human activity in today was 100, and worked out the average impact of human activity in past 2 000 years was 6.20, the average impact of human activity before the middle of Qing dynasty was 2.79, the average impact of human activity since the middle of Qing dynasty was 22.50 and the average impact of human activity since the past 45 years was 67.90. The level of impact of human activity in the middle of Qing dynasty reached 18% of present impact; it was consumedly exceeded its past; it compared with the impact of climatic change, fingered out the contribution of human activity; the average contribution of human activity in past 2 000 years was 24.4%, the average contribution of human activity before the middle of Qing dynasty was 19.2%, the average contribution of human activity since the middle of Qing dynasty was 48.9% and the average contribution of human activity since the past 45 years was 81.6%.