Flood is any flow of water, which overflows the natural or artificial banks of a body of water. Flooding is one of the fundamental environmental challenges that results from interaction between man and his environment...Flood is any flow of water, which overflows the natural or artificial banks of a body of water. Flooding is one of the fundamental environmental challenges that results from interaction between man and his environment. In Nigeria, Flooding is one of the most common environmental hazards and there is increasing vulnerability of populations and infrastructure to flooding and flood related hazards. This study used GIS as a tool to analyze the cause and the impact of flooding in the study area. The study used both primary and secondary data, through a questionnaire, geographic information system and remote sensing. The result showed that the nature of the basin in the study area resulted to the high volume of water in the major river (River Osun) during raining season, which resulted to overflow across its bank. Fieldwork shows that the river overflows its bank at 500 meters to the north and the south and the GIS analysis shows that over 1000 houses get affected at any point of flooding occurrences, hence the width of the river is less than 8 meters and the depth on the average in less than 10 meter over the bridge of the River Osun. The study recommends methods by which flooding could be controlled in the study area through regular dredging, effective waste management and drainage control.展开更多
The homogeneous hidden Markov model(HMM), a statistical pattern recognition method, is introduced in this paper. Based on the HMM, a 53-yr record of daily precipitation during the flood season(April-September) at 389 ...The homogeneous hidden Markov model(HMM), a statistical pattern recognition method, is introduced in this paper. Based on the HMM, a 53-yr record of daily precipitation during the flood season(April-September) at 389 stations in East China during 1961-2013 is classified into six patterns: the South China(SC) pattern, the southern Yangtze River(SY) pattern, the Yangtze-Huai River(YH) pattern, the North China(NC) pattern, the overall wetter(OW) pattern, and the overall drier(OD) pattern. Features of the transition probability matrix of the first four patterns reveal that 1) the NC pattern is the most persistent, followed by the YH, and the SY is the least one; and 2) there exists a SY-SC-SY-YH-NC propagation process for the rain belt over East China during the flood season. The intraseasonal variability in the occurrence frequency of each pattern determines its start and end time. Furthermore,analysis of interdecadal variability in the occurrence frequency of each pattern in recent six decades has identified three obvious interdecadal variations for the SC, YH, and NC patterns in the mid-late 1970 s, the early 1990 s, and the late 1990 s. After 2000, the patterns concentrated in the southern region play a dominant role, and thus there maintains a "flooding in the south and drought in the north" rainfall distribution in eastern China. In summary, the HMM provides a unique approach for us to obtain both spatial distribution and temporal variation features of flood-season rainfall.展开更多
利用1961—2013年华南区域305个国家级气象台站日降水资料、1980—2013年5—6月NCEP/CFSR再分析资料（分辨率0.5×0.5）等,定义华南前汛期持续性暴雨和暴雨持续日数,分析近53 a华南前汛期持续性暴雨特征及其大尺度环流形势;归纳有...利用1961—2013年华南区域305个国家级气象台站日降水资料、1980—2013年5—6月NCEP/CFSR再分析资料（分辨率0.5×0.5）等,定义华南前汛期持续性暴雨和暴雨持续日数,分析近53 a华南前汛期持续性暴雨特征及其大尺度环流形势;归纳有利于华南前汛期持续性暴雨发生的4种典型环流类型。结果表明：（1）华南前汛期持续性暴雨过程主要集中在5—6月,并存在准20 a振荡周期;1960年代前半段6月暴雨次数多,1960年代末期到1980年代5月暴雨次数明显增加,1990年代至2013年暴雨主要出现在6月,2006年后5月暴雨次数逐渐增加;暴雨过程持续日数一般3~4 d,超过10 d以上的单次过程仅4次。（2）华南前汛期持续性暴雨分为东亚槽底型、两脊一槽型、多涡旋型和纬向型,东亚槽底型和两脊一槽型次数相对较多,主要发生在5月下旬—6月下旬;纬向型次数最少,主要在5月上旬—6月初。（3）各型持续性暴雨过程500 h Pa中高纬地区环流特征各异,其共性是均有利于北方冷空气南下影响华南,低纬地区西太平洋副热带高压（副高）和孟加拉湾南支低槽维持少动,低层850 h Pa华南盛行西南暖湿急流;持续10 d左右的暴雨过程相较持续3~5 d的暴雨过程,副高位置偏西偏强,华南上空多短波槽活动,850 h Pa西南季风气流位置偏西偏北、风速偏大。展开更多
文摘Flood is any flow of water, which overflows the natural or artificial banks of a body of water. Flooding is one of the fundamental environmental challenges that results from interaction between man and his environment. In Nigeria, Flooding is one of the most common environmental hazards and there is increasing vulnerability of populations and infrastructure to flooding and flood related hazards. This study used GIS as a tool to analyze the cause and the impact of flooding in the study area. The study used both primary and secondary data, through a questionnaire, geographic information system and remote sensing. The result showed that the nature of the basin in the study area resulted to the high volume of water in the major river (River Osun) during raining season, which resulted to overflow across its bank. Fieldwork shows that the river overflows its bank at 500 meters to the north and the south and the GIS analysis shows that over 1000 houses get affected at any point of flooding occurrences, hence the width of the river is less than 8 meters and the depth on the average in less than 10 meter over the bridge of the River Osun. The study recommends methods by which flooding could be controlled in the study area through regular dredging, effective waste management and drainage control.
基金Supported by the National Natural Science Foundation of China(41675081)National Key Research and Development Program of China(2017YFA0603804)
文摘The homogeneous hidden Markov model(HMM), a statistical pattern recognition method, is introduced in this paper. Based on the HMM, a 53-yr record of daily precipitation during the flood season(April-September) at 389 stations in East China during 1961-2013 is classified into six patterns: the South China(SC) pattern, the southern Yangtze River(SY) pattern, the Yangtze-Huai River(YH) pattern, the North China(NC) pattern, the overall wetter(OW) pattern, and the overall drier(OD) pattern. Features of the transition probability matrix of the first four patterns reveal that 1) the NC pattern is the most persistent, followed by the YH, and the SY is the least one; and 2) there exists a SY-SC-SY-YH-NC propagation process for the rain belt over East China during the flood season. The intraseasonal variability in the occurrence frequency of each pattern determines its start and end time. Furthermore,analysis of interdecadal variability in the occurrence frequency of each pattern in recent six decades has identified three obvious interdecadal variations for the SC, YH, and NC patterns in the mid-late 1970 s, the early 1990 s, and the late 1990 s. After 2000, the patterns concentrated in the southern region play a dominant role, and thus there maintains a "flooding in the south and drought in the north" rainfall distribution in eastern China. In summary, the HMM provides a unique approach for us to obtain both spatial distribution and temporal variation features of flood-season rainfall.
文摘利用1961—2013年华南区域305个国家级气象台站日降水资料、1980—2013年5—6月NCEP/CFSR再分析资料（分辨率0.5×0.5）等,定义华南前汛期持续性暴雨和暴雨持续日数,分析近53 a华南前汛期持续性暴雨特征及其大尺度环流形势;归纳有利于华南前汛期持续性暴雨发生的4种典型环流类型。结果表明：（1）华南前汛期持续性暴雨过程主要集中在5—6月,并存在准20 a振荡周期;1960年代前半段6月暴雨次数多,1960年代末期到1980年代5月暴雨次数明显增加,1990年代至2013年暴雨主要出现在6月,2006年后5月暴雨次数逐渐增加;暴雨过程持续日数一般3~4 d,超过10 d以上的单次过程仅4次。（2）华南前汛期持续性暴雨分为东亚槽底型、两脊一槽型、多涡旋型和纬向型,东亚槽底型和两脊一槽型次数相对较多,主要发生在5月下旬—6月下旬;纬向型次数最少,主要在5月上旬—6月初。（3）各型持续性暴雨过程500 h Pa中高纬地区环流特征各异,其共性是均有利于北方冷空气南下影响华南,低纬地区西太平洋副热带高压（副高）和孟加拉湾南支低槽维持少动,低层850 h Pa华南盛行西南暖湿急流;持续10 d左右的暴雨过程相较持续3~5 d的暴雨过程,副高位置偏西偏强,华南上空多短波槽活动,850 h Pa西南季风气流位置偏西偏北、风速偏大。
