Spatio-temporal process of oasification in the middle-Heihe River basin during 1368–1949 AD, China

Understanding the oasis evolution process is one of the most important theses in arid regions, which could provide correlative theories for oasis exploitation. Currently, the researches implemented by a single method of document analysis with invisible results restricted the vision. By integrating and synthesizing records from historical documents, satellite images, local chronicles and maps, the spatial-temporal variability of oasification for nearly 600 years (1368–1949 AD) in the middle-Heihe River basin in western China was reconstructed. The conclusions are as follows: first, the oasis area in the five main periods, namely, the Early Ming, the Late Ming, the Early Qing, the Late Qing, and the Republic of China were 964, 840, 1205, 932 and 1917 km², respectively. Second, the oasis expanded during the Early Ming and Early Qing Dynasties as well as the Republic of China, whereas the intervenient periods namely, the Late Ming and Late Qing Dynasties shrunk. Third, the cultivated oasis sprawled out from the existing settlements established in the early Ming to surroundings, and the main sprawling period occurred in the early Qing in the downstream of the Taolai River, whereas the other oasis expansion appeared in the intermediate area of existing oases. It is indicated that the oasis distribution was restricted by the distribution of water resources and the oasification process is the result of climate change, political situation and policy as well as changes of population. The oasification process shows the active and adverse effects. The results describe a range of oasis conditions from 1368 to 1949 and provide a historical framework for measuring associated changes in ecosystems, which can be used to guide restoration where feasible and desirable.