关键词: 巢湖流域, 旱涝灾害, 旱涝等级, 功率谱分析

Abstract:

Based on listing systematically the historical records of the Chaohu Lake Basin’s drought and flood, and integrating the data of 7 counties (cities) on watershed flood and drought indexes and its grades, a graded series of dryness/wetness during the past 600 years has been rebuilt to calculated the drought and flood frequency. The results of continuous power spectrum analysis reveal the rules and cycles of dryness/wetness change within the Basin. In comparison with the dryness/wetness series of mid-downstream basin of the Changjiang River and the watershed climatic change in temperature, then the impacts on environment change by natural factor and human exploitation can be indicated. The main conclusions are as follows: 1) In past 600 years, the disaster of flood and drought usually occurred within the Chaohu Lake Basin, and its average frequency was once-in-1.88 years. The frequency of flood was nearly equivalent to that of drought, but the frequency of heavy and great flood was higher than that of heavy and great drought. From the time perspective, the frequency of drought was higher than that of flood before the 19th century; flood was more serious than drought in the 19th century. But to the 20th century, this trend reversed. Moreover, it is a remarkable character that the great drought and great flood appeared 2 to 3 years continuously within the Chaohu Lake Basin in this period. 2) The result of continuous power spectrum analysis demonstrates that there were the 2 or 3-year and 7-10-year fluctuations among them within the Chaohu Lake Basin. The period from the 1920s to the 1960s was the worst drought period within the Chaohu Lake Basin over 600 years. In contrast, the period from the 1820s to the 1860s was the most serious flood period. By the dryness/wetness disaster time series’ fitting on the Chaohu Lake Basin and the Changjiang River mid-downstream Basin, it is found that there was an approximate synchronous variation of disaster occurrence between them. It is also proved that the Chaohu Lake Basin is the commendable indicator of dryness/wetness variation within the Changjiang River mid-downstream Basin. With the advent of agriculture, and the large-scale developing of industry, especially during the past 2 hundred years, the number and activity of the human species increase sharply, so that the mankind intervenes more strongly to environment. Some estimate that the impacts on environment of human activity has been the same degree as that of natural evolutionary process, but so far there is no conclusion on which is more important. Precious curve-fitting illustrated that the environmental evolution within the Chaohu Lake Basin is mainly limited by climate change. Although the degree of human intervention is deepening, it is just one inducement to environmental evolution. 3) There is a certain relationship existing between the occurrence of drought/flood and the regional climatic change in temperature. Before the 1830s, drought often happened in the cool periods, while flood often happened in the warm periods. But the relationship had broken down after the 1830s, and it was characterized by flooding and drought coming by turns, which is the direct result caused by deepening human activity. These viewpoints need to be proved by further research work.

Key words: Chaohu Lake Basin, flood and drought disasters, degree of flood and drought, power spectrum analysis