| At present, global change is a global issue that the international community generally pay attention to, and it is also a core issue of global environmental problems, at the same time, droughts disasters are concerned in global change.Fenhe River, known as the "Mother River" in Shanxi Province, is the second largest tributary inferior to Weihe River, and it is the largest and the longest river in Shanxi Province. At the same time, Fenhe river is a world-famous multi-sediment river, its frequent rechanneling with drought and floods in middle and low reaches had brought great pain and suffering to people living along the river. Therefore, this paper deals with droughts and floods level, spatial and temporal distribution, causes of disasters through history documents, interview survey, methods of quantitative geography,wealthy literature about disaster and modern statistical data in Fenhe River between 730 B.C. and 2000 A.D..The main results as following:(1) Droughts and floods level of Fenhe River basin were divided into four grades based on qualitative description of historical documents of disaster situation as the main target, according to the duration of droughts and floods, intensity, damage area and damage extent and based on the description of drought and flood disasters by historical literature about Fenhe river. Three periods each year droughts and floods were graded in accordance with the hierarchical sequence in Fenhe river basin above the Ming, Qing and 1911-2000, the conclusions were:The occurring frequency of drought disasters at grade first and second level were the highest, and at grade third and fourth were higher in Ming Dynasty. According to the grade series of drought disasters, the less occurring frequency of drought disasters occurred in early Ming Dynasty, the disaster increased obviously in the middle and late period of Ming Dynasty, drought disaster occurred in higher frequency in Ming Dynasty; According to the grade series of drought disasters, the occurring frequency of flood disasters at grade first was the highest, and then at second and third grade in Qing Dynasty, and the fourth grade was the lowest; the occurring frequency of drought disasters at grade second were the highest, then at first third and fourth in 1911-2000 Dynasty.The occurring frequency of flood disasters at grade second, first and third were the highest, and at grade third and fourth was low in Ming Dynasty and in Qing Dynasty; the occurring frequency of flood disasters at grade second, and then that at third grade, at grade fourth was low, and at grade first was least in Ming Dynasty.(2)According to the number of occurrences and thends, drought history of the evolution process of the Fenhe river is divided into five periods:①Less droughts period,7th century B.C. to the 3rd century B.C., disasters record low, and the disasters cycle was not obvious.②Growing period,2nd century B.C., a higher incidence of disasters.③Cumulative period,1st centery B.C. to 4th century A.D., the number of disasters record was gradually increasing.④No disaster, during the 5th century A.D., non-disaster recorded.⑤Passively increasing,6th century A.D. to 20th century A.D., the number of disasters since 6th century A.D. significantly increased, during this period disasters the overall number of occurrence firstly decreased and then increased volatility increase. The number of disasters in the 19th century A.D. and 20th century A.D. reached the maximum.According to the number of occurrences and thends, the flood history of the evolution process of the Fenhe river is divided into four periods:The period of less floods,8th century B.C. to 1st century A.D., disasters rarely recorded, strong undulating disaster, and cycle was not obvious.The period of floods increasing,2nd century A.D.to 6th century A.D., the number of disasters begin to increase.The period of floods deincreasing,7th century A.D. to 13th century A.D., the number of disasters record was less than before.More flood period,14th century A.D. to 20th century A.D., the number of recorded disasters increased substantially.(3) It was concluded according to seasonal distribution from drought and floods through 2000 years in Fenhe River:The droughts of Fenhe River during this period were mainly spring drought and summer drought, droughts also had higher incidence in spring, in summer and in autumn. Droughts were fewer in the up stream, drought occurred more in summer and in spring and summer. Drought occurred frequently in the middle and down stream; spring drought. Summer drought and the drought occurred more frequently in the middle stream, and droughts were followed in autumn and in summer. Droughts occurred most frequently in the down stream, and droughts were followed in spring, summer and autumn.During this period the flood disasters of Fenhe River occurred in summer and autumn, rarely occurred in spring. Droughts were little in the upstream, summer floods more, autumn floods followed, spring floods was the least. Droughts occurred the most often in the middle stream, the summer floods was the most, autumn floods and spring floods followed. Downstream was less than the middle, mainly was summer floods, autumn floods followed and spring floods occurred few.(4) In this paper, it was concluded abuout counties where drought disasters happened in Fenhe River basin from 730 B.C. to 2000 A.D.:Cities and counties of Fenhe River had greater frequency of occurrence drought disasters, which mainly occurred in the middle of Fenhe River including Taiyuan, Jiexiu, Pingyao, Yuci, and Wenshui; downstream of Linfen, Quwo, Xiangfen, Hongtong and Wanrong county; upstream occurred less frequently.The counties of floods were mainly in the upper reaches, especially in Taiyuan, Pingyao, Jiexiu, Fenyang, Wenshui and Jiaocheng, and Linfen in downstream Fenhe river these six counties suffered the most frequently, followed by the middle of Fenhe River, Yangqu, Shouyang, Yuci, Taigu, Qixian, Lingshi, Qingxu, Xiaoyi, and Hongtong, Xiangfen, Yicheng, Xinjiang, Quwo, Wanrong, Hejin in the downstream are also easier to form disasters; the upstream:Ningwu, Jingle, Lanxian, Loufan, Gujiaoc., the middle downstream including Jiaokou,Fenxi, Guxian, Huozhou, as well as the downstream including Houma, Fushan, jishan were less affected by flood disasters.The causes of drought and flood disasters in Fenhe river from 730 B.C. to 2000 A.D.were: natural factors,human factors and climate fluctuation.Basin topography and meteorological factors in Fenhe river were major naturaimpacts.The impact of droughts and floods abuout human factors in Fenhe river showed human vegetation damage, aggravating soil erosion and deterioration of ecological environment, combined with the river basin increasing silt content, will inevitably lead to the rivers, frequent droughts and floods. Fluctuation of the climate change had greatly affected floods and droughts in Fenhe river... |
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