ZHANG Xue-qin, GE Quan-sheng, LIN Zhen-yao
The Xizang Autonomous Region, one part of the Qinghai-Xizang Plateau, is characterized by high elevation, complex topography, and frequently occurred natural disasters (e.g., flood, drought, storm, hail, and frost, etc.), which has huge impacts on the development of agriculture and animal husbandry over the plateau. It is rather important to study the climate change over the Xizang Plateau using historical documents for a better understanding of the plateau's climate and its connection with the global climatic changes. First, the accuracy of historical archives in chronological record can provide accurate time for the study of historical climate change about the plateau. Second, the typical hazardous events (e.g., severe drought/flood, warm/cold) and abrupt climatic change extracted from historical archives can well support the peak and/or valley of series of environmental changes. Third, by searching for the relation of data between the plateau and east part of China embedded in historical documents, the climate change over the plateau can be deduced basing on the rich data of the east part of China. Finally, past climatic environmental series can be reconstructed by synthesizing proxy records as many as possible, which will reduce distortion and improve the accuracy of reconstruction of climatic environmental series.Based on the introduction of data and method used in the paper, the spatio-temporal characteristics of flood in Xizang for the historical documents covered period of 1803-1958 A.D. are analyzed as follows. Firstly, the frequency of flood fluctuated significantly for Xizang from the early 19th century to the 1950s, flood occurred frequently within 1840s-1880s, and severe flood occurred in 1924 and 1954. Secondly, the spatial distribution differentiation of flood in Tibet is obvious, which mostly occurred in the "Yarlung Zangbo-Lhasa-Niyang Rivers" region. Among them, the flood occurred most frequently in Xigaze, Shannan Prefectures following Lhasa City and Nyingch Prefecture, while flood occurred relatively little in Qando, Ali, and Nagqu Prefectures. Thirdly, the high-intense-continuous precipitation is the key factor of flood in Xizang, the sudden and sharp rise, overflow, and riverway change of river are important media, landslide, snowslide, mountain onrush, debris flow, etc. are major factors inducing flood under particular geomorphologic condition, and hail, groundwater discharge, etc are factors not neglected. Fourthly, it was humid for Xizang climate during the period from 1940s to 1980s. In a word, it's reliable and valuable to study the flood of Xizang by using the disaster historical materials especially Xizang's disaster historical documents and diaries. Though the historical materials covered only from 1803 to 1958 A.D., they still reflected the disaster condition of this period for Xizang. We hope to be helpful to the current production of agriculture animal husbands, and disaster prevention and relief in Xizang by the further genetic analysis of flood.
