Remote Sensing Investigation On Remains Of Human Activities Of Downstream Heihe River In Historical Period

Oasis is a unique geographical landscape, which is an important region for supporting the human life and agricultural production in arid zone. Due to the driving forces by natural factors and human activities in different historical periods, ecological environments of the ancient oases have undergone great changes over the past2000years in arid regions, northwestern China. Particularly, oases have undergone serious desertification. History is a mirror to be compared with the present, and the current oases have relations with the ancient oases during the past times. In order to protecting the arid ecological environment and utilizing the limited resources in the basin, it is very important to conduct the research of past human activities and ancient oases evolution. It also has great significance for the basin and oases to be sustainable development.Heihe River Basin is one of the important inland river basins in arid regions of northwestern China, and Ejin River Basin is the lower reaches of this river. The ancient Juyan region is located in the downstream of Ejin River Basin, which has a long history of human activities. This region was lush and suitable for livestock breeding, where was the nomadic areas of Northern Huns before the Han Dynasty. The ancient Juyan region belonged to the territory of the Central Plains during the Western Han Dynasty. The natural oasis was first large-scale developed by construction of the military facilities, resettlement and protection the frontiers, build the water conservancies, reclamation and irrigation, establishment of local governments, which caused the dramatic changes in land use and land cover in the ancient Juyan Oasis. Another large-scale human agricultural activities was performed during the Western Xia and Yuan Dynasties thereafter some changes during different historical periods, i.e., Wei and Jin Dynasties, Sui and Tang Dynasties. After the demise of the Yuan Dynasty, the ancient Juyan region was abandoned to be the exclusive area of Jiuquan and Zhangye Citities in the Hongwu Reign of the Ming Dynasty, and the human activities were almost disappeared. Human activities in this region appeared once again until the return of Old Tuerhute’s Tribal people, living downstream of Heihe River Basin in the Qianlong Reign of the Qing Dynasty. However, the nomadic livings of the Old Tuerhute were moved to the Ejin Oasis due to the desertification of the ancient Juyan Oasis. Now, desertification of the ancient Juyan Oasis is intensified, and the desertified area is constantly expanding. A large number of archaeological remains that reflected past human activities exist among the numerous nebkhas and sand dunes. The Han Dynasty and the Western Xia and Yuan Dynasties were selected to be the main periods to conduct this study. Historical documents, previous archaeological reports, multi-sources remotely sensed data and field investigations were combined to conduct this research. All of the doctoral dissertation works are comprised of below:1. According to the documents recorded in many previous archaeological reports over the past one hundred years, the databases of the archaeological sites of past human activities in the downstream of the Heihe River Basin were established during the Han Dynasty and Western Xia and Yuan Dynasties, respectively. These new databases avoid many shortcomings of the traditional management method for archaeological sites, e.g., inefficiency management, difficulty to update and edit, easily lose and damage. The databases include the spatial locations and the attributions of the archaeological sites. It is very useful and convenient to conduct the following operations for the archaeological sites in the databases, including management, view, update, edit and analysis.2. It is difficult for the traditional outdoor archaeology to cover all of the investigated areas. Particularly, investigators are difficult to access some severe desertification region. It is impossible for the traditional surveys to find those ruins of past human activities with small shapes that are dispersed and covered in the nebkhas and sand dunes. After the field in-truth validation using sampling sites, it is found that the high-resolution remote sensing imagery can play an important role in identification of the archaeological sites in the desertification environment. These new sites obtained from the remotely sensed data have greatly enriched the database of the archaeogical sites and provided important additional information to conduct the study of past human activities.3. Ancient artificial irrigation canals were identified and extracted using high-resolution remote sensing imagery. Spatial quantitative distribution of the agricultural irrigation canals was mapped in the ancient Juyan Oasis. These foundings imply that the oasis had been well-developed irrigated agriculture with large areas during the historical periods. After comparing with the modern irrigation systems. it is shown that the agricultural irrigation system has the similarities between the ancient irrigation methods and the modern irrigation system in arid region of northwestern China, which both develope the hierachical irrigation systems to irrigate farmlands. However, the raw materials and the construction styles are different.4. Lvcheng reclamation area was the largest sub-region to conduct the agricultural activities in the oasis. Ancient irrigation canals in this region are the best well-preserved in the ancient Juyan Oasis, and it can be seen as a microcosm and typical represent of the historical irrigation farming in the study area in historical period. According to the spatial relationships between the archaeological sites and the agricultural irrigation canals, as well as the remaining conditions of the irrigation canals, it can be speculated that mcst of the remains of artificial irrigation canals could be mostly built and used during the Western Xia and Yuan Dynasties in the Lvcheng reclamation area.5. Based on the spatial distributions of the large number of the archaeological remains that reflected past human activities, the spatial extent of ancient agricultural oasis was determined and extracted in the Han Dynasty and the Western Xia and Yuan Dynasties, respectively. Furthermore, according to the concept and values of the arable land coefficient that are used in modern researches of land use change in arid regions of northwestern China, the value of non-arable land factor was roughly conservatively estimated at a minimum of30%～50%in the ancient Juyan Oasis. Then, it is calculated that the farmland area was approximately (3.39～4.75)×104ha in the Han Dynasty and the farmland area was approximately (2.18～3.05)×104ha in the Western Xia and Yuan Dynasties.