| Upstream area of Hanjiang River, which is the largest branch of Yangtze River,.is located at south of Qingling Mountains and north of Daba mountains. It is the north boundry of subtropical zone in China, connected to warm temperate zone, and the sensitive and fragile area of ecological environment. Danjiangkou Reservoir, which is located at upper reaches of Hangjiang River, is the water source of middle route of South-to-North Water Transfer Project. Water resources of this area are directly or indirectly impacted by flood, drought, and freezing disasters. In order to cross-area allocate and rationally utilize water resources in China, it is important to research the regularity of the main meteorological disasters in historical times of this area. Since ancient times, drought, flood, and freezing disasters have influenced human production and life greatly, especially when the disasters occurred frequently and influenced widely. They could produce profound impact on economic development and society stability, and even lead to perish of dynasties. At the same time, it is conducive to prevent agricultural meteorological disasters in the area between subtropical zone and warm temperate zone, provide decision support of prevention and reduction of disasters, and promoter sustainable development of agriculture through statistical analysis of main disasters in this area.The main research data base of this thesis is based on the historical records of major meteorological disasters, such as droughts, floods, freezing, at upstream of the Hanjiang River. First of all, with the help of Excel, DPS and Matlab, outbreak regularities, including frequency, season and month characteristic, and cycle characteristic, of the three main disasters were analyzed. Secondly, spatial regularities of the three disasters were analyzed by using ArcGIS. Thirdly, the correlation analysis was executed to explore the general rules and characteristics of the three disasters on the SPSS software platform. At last, the social effects of the three disasters were researched through correlation analysis. The main conclusions of this thesis are as following.(1) Flood disaster, followed by drought and freeze disaster, was occurred most frequently in historical period at upper reaches of Hanjiang River. Flood disaster, which has apparent time change characteristic, occurred323times at an average of6.81a once. A lot of flood disasters occurred in Daoguang Period and Guangxu Period of Qing Dynasty, and later period of the Republic of China. Flood disasters focused in April, June, July, August and September, and accounted for90.56%of the total. The order of occurrence frequencies is autumn, summer, spring and winter in season. Flood disasters, which were declined from Ankang Basin to periphery, have the difference of Spatial characteristic. They happened most in the valley of upstream of the Hanjiang River. Moderate floods and severe flood happened most in disaster grade aspect. Extra severe floods lagged behind severe floods in occurrence time. Flood disasters had persistent effect on human life and production. The main reasons of flood disasters in the upper reaches of the Hanjiang River are intensity and seasonal variation of rainfall caused by atmospheric circulation, topography, vegetation cover rate, and the impacts of human activities.(2) Drought disasters happened303times in all at an average7.19a once.At the change of time, drought disaster occurrence increased fluctuated. Drought disasters happened most frequently since Qing Dynasty. Drought disasters are divided into three stages. The first stage is before809A D. Drought disasters happened at low frequency and small fluctuate at an average of61.11a once. The peaks happened at280-329A D and680-689A D. The second stage is between from810to1749. Drought disasters happened frequently and increased fluctuanted. The third stage is from1750to1990. Drought disasters happened most frequently in this period at an average of1.83a once. The order of occurrence frequencies is summer, spring, autumn and winter from the aspect of season and moth. Drought disasters happened most in June. The years of Seasonal drought (Spring-summer droughts and summer-autumn droughts) were corresponding with the years of severe drought and extra severe drought. From the aspect of periodic variation characteristic, drought disasters have large scale period of50a,90-100a,150a,180a and220a, and unapparent periodic variation of2-5a. Low latitude ocean atmospheric activity and solar activity are two of the causes of drought disaster.(3) Freezing disasters, which occurred in the lowest frequency of the three meteorological disasters, happened104times at an average of18.94a once in Upper reaches of the Hanjiang River region. Freezing disasters also have obvious stage. The first stage is about before1439. Freezing disasters have lowest frequency and small fluctuate, and happened at an average of202.85a once. The Peaks occurred at20-29a,290-299a,420-439a,810-819a,1180-1189a and1290-1299a. The second stage is between1440and1919. Freezing disasters happened in relatively high frequency and at an average of1.4a once. The third stage, which has the highest occurrence frequency of freezing disaster at an average of1.27a once, is from1920-1990year. Freezing disasters happened in high frequency with a obvious trend of fluctuated increasing. From the aspect of season, freezing disaster happened most in spring, and the main disasters were frost. From the aspect of grade, moderate freezing disasters were in majority, and mild and severe freezing disaster is relatively low. From the aspect of time, all levels of freezing disasters have experienced and three stages frequency variation-lowest period, relatively high period, and highest period. Freezing disasters have obviously spatial distribution differences. Xunyang, followed by Zhenan, Liuba, Zhashui, happened most frequently. Yunxi, Hanyin, Shiquan and Langao happened fewest.(4) There are significant correlations among the main meteorological disasters of upper reaches of Hanjiang River in historical period. There is a significant positive correlation between drought disaster and flood disaster. The correlation coefficient reaches0.994. There is a significant positive correlation between freezing disaster and flood disaster, the same as the correlation between freezing disaster and drought disaster. The correlation coefficients are0.91and0.896respectively. When freezing disasters occurs more, flood and drought disaster also happened more. The main meteorological disasters have characteristics of group-occurred and less-occurred. Different kinds of meteorological disasters would increase during periods of climate deterioration and instability. The destroy strength was large and it had tremendous impact on society and politics. In this thesis, we think that there are some defects and limitations to deduce the climate according to the frequency and influence of the disasters at that time. It can be used as references, when historical and modern climate is studied. In order to analyzing scientifically and effectively, and get more accurate and reliable conclusion, other reference values and data need to be added.(5) Influences of Disasters of flood, drought and freezing to human society mainly include agricultural production and ecological environment, war, population development, human health, capitals and removal, et al. Significant impacts to development of society are not caused by single extreme climate event, but by two or more disasters. The ability to response to the three disasters was closely related to the development of society productiveity. |
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