1470-1912年西北东部地区极端干旱事件的复原及分形特征研究

通过对西北东部地区1470-1912年干旱灾害历史资料的搜集整理，根据干旱发生强度、持续时间、发生范围，定义了强旱事件，建立了极旱因子模型，复原了443年西北东部地区极端干旱事件，并根据时间分形原理，挖掘出极旱事件时间序列的分维特征。经过对比分析得到以下结论：建立的模型结果与记载结果具有显著的相似性；全序列旱灾时间分维值随极旱强度的增加而降低，与极旱发生周期呈反位相关系；各类别极旱有自己的时间重演律，极旱程度越轻，无标度区越宽，分维值越高，短周期比较明显。

Recovery of extreme drought events and their fractal characteristics in the eastern Northwest China from 1470 to 1912

Northwest China has the lowest quantity of precipitation in the same latitude of the Northern Hemisphere and its main climatic disaster is drought. By using rich literature historical records in China to rebuild the chronology of extreme drought events and increase research on the evolution law of the drought not only can provide historical similarity of extreme climatic events that may occur in the future, but also has the important significance and value for preventing disasters and reducing damages. Because of the complexity of extreme drought, the simple linear theory and research methods can't meet the research of the complex system of natural disasters. In this paper, we used fractal theory to reproduce the original research object and research the self-similarity of extreme drought system. Studying the similarity of whole and partial, and finding the new order between macro and micro, between entirety and parts, can deepen our understanding of the characteristics of extreme drought and provide a new method to analyze the reasons of extreme drought events. Through collecting historical data about drought disasters from 1470 to 1912 in the eastern northwest China and the drought intensity, duration and range, we defined heavy drought events, built the factor model of extreme drought, reconstructed the extreme events of eastern northwest China for 443 years. Furthermore, by using scale transformation method, this paper calculated the time fractal dimension of different kinds of extreme droughts from 1470 to 1912 in the eastern northwest China, and mined the time series fractal dimension characteristics of extreme drought events and the relationship between fractal dimensions and distribution structure by using the least squares method, which is of great significance for overall understanding the regularity of occurrences of extreme drought events in northwest China and its occurrence and countermeasures. The results show:(1)There were 22 extreme drought events from 1470 to 1912, among which extreme drought of type I has the largest times, type II is second and type III is the least.(2)The temporal fractal dimension of the drought disasters of the whole series reduces with the increasing of extreme drought intensity, shows inverse correlation with extremely drought period. Different types of extreme drought events have their own recapitulation law in time domains: the lighter the drought degree is, the wider the scale-free area is; the higher the fractal dimension is, the more obvious the short period is. Extreme drought disasters have different levels and they have their respective time recapitulation law: the lower the level is, the shorter the time recapitulation law will be.(3)In the entire period, the dynamic of different levels of the extreme drought disasters present that the overall extreme drought, type I and type III underwent a series of evolution that occurred from disordered to ordered, and then gradually to non-equilibrium conditions from disordered to ordered; while the early type II distributed more orderly and then went into the state of disordered, finally its fractal dimension decreased and its extreme drought events became more concentrated.