Extreme flood events are becoming more frequent and intense in recent times, owing to climate change and other anthropogenic factors. Nigeria, the case-study for this research experiences recurrent flooding, with the ...Extreme flood events are becoming more frequent and intense in recent times, owing to climate change and other anthropogenic factors. Nigeria, the case-study for this research experiences recurrent flooding, with the most disastrous being the 2012 flood event that resulted in unprecedented damage to infrastructure, displacement of people, socio-economic disruption, and loss of lives. To mitigate and minimize the impact of such floods now and in the future, effective planning is required, underpinned by analytics based on reliable data and information. Such data are seldom available in many developing regions, owing to financial, technical, and organizational drawbacks that result in short-length and inadequate historical data that are prone to uncertainties if directly applied for flood frequency estimation. This study applies regional Flood Frequency Analysis (FFA) to curtail deficiencies in historical data, by agglomerating data from various sites with similar hydro-geomorphological characteristics and is governed by a similar probability distribution, differing only by an “index-flood”;as well as accounting for climate variability effect. Data from 17 gauging stations within the Ogun-Osun River Basin in Western Nigeria were analysed, resulting in the delineation of 3 sub-regions, of which 2 were homogeneous and 1 heterogeneous. The Generalized Logistic distribution was fitted to the annual maximum flood series for the 2 homogeneous regions to estimate flood magnitudes and the probability of occurrence while accounting for climate variability. The influence of climate variability on flood estimates in the region was linked to the Madden-Julian Oscillation (MJO) climate indices and resulted in increased flood magnitude for regional and direct flood frequency estimates varying from 0% - 35% and demonstrate that multi-decadal changes in atmospheric conditions influence both small and large floods. The results reveal the value of considering climate variability for flood frequency analysis, especially when non-stationarity is established by homogeneity analysis.展开更多
The flood and drought across the Yangtze and Huaihe River（Jianghuai） areas are frequent in summer, especially in June and July.Therefore,predicting the summer flood and drought in the Jianghuai region is always one ...The flood and drought across the Yangtze and Huaihe River（Jianghuai） areas are frequent in summer, especially in June and July.Therefore,predicting the summer flood and drought in the Jianghuai region is always one of the key topics concerned by meteorologists in China.Previous studies focused more on the skin temperature anomalies in a local area,and paid less attention to the connections between the anomalies of land-sea thermal contrast in remote continents and the summer flood and drought in Jianghuai areas of China.By using the US NCEP/NCAR monthly mean reanalysis data and the rainfall data at 743 stations in China,based on the interdecadal variation characteristics of the flood and drought index（FDI） during 51 yr （1954-2004） in the Jianghuai region of China in summer,the North African areas have been selected as the key regions for the correlation analysis.The results show that the surface temperature anomalies in the key regions have good continuity in winter,and the winter North Atlantic Oscillation（NAO） is perhaps one of the important factors that bring about the continuity of the anomalies.By a singular value decomposition（SVD） analysis between the skin temperature in the previous winter in North Africa and the summer rainfall in the Jianghuai region,it is found that when the North African continent is colder（warmer） and its northwestern sea is warmer（colder）,the rainfall increases（decreases） in the Jianghuai region in summer generally.Further analysis finds that the anomaly of the surface temperature contrast between sea and land in North Africa has a good indication for the summer flood and drought in the Jianghuai areas of China.Therefore,a sea and land thermal contrast index（SLTCI） is defined to reflect the intensity of the large-scale land-sea thermal contrast.A positive correlation between the SLTCI in North Africa and the summer FDI in Jianghuai areas is identified,and it can well indicate the extreme flood and drought situations in the Jianghuai region of China.展开更多
文摘Extreme flood events are becoming more frequent and intense in recent times, owing to climate change and other anthropogenic factors. Nigeria, the case-study for this research experiences recurrent flooding, with the most disastrous being the 2012 flood event that resulted in unprecedented damage to infrastructure, displacement of people, socio-economic disruption, and loss of lives. To mitigate and minimize the impact of such floods now and in the future, effective planning is required, underpinned by analytics based on reliable data and information. Such data are seldom available in many developing regions, owing to financial, technical, and organizational drawbacks that result in short-length and inadequate historical data that are prone to uncertainties if directly applied for flood frequency estimation. This study applies regional Flood Frequency Analysis (FFA) to curtail deficiencies in historical data, by agglomerating data from various sites with similar hydro-geomorphological characteristics and is governed by a similar probability distribution, differing only by an “index-flood”;as well as accounting for climate variability effect. Data from 17 gauging stations within the Ogun-Osun River Basin in Western Nigeria were analysed, resulting in the delineation of 3 sub-regions, of which 2 were homogeneous and 1 heterogeneous. The Generalized Logistic distribution was fitted to the annual maximum flood series for the 2 homogeneous regions to estimate flood magnitudes and the probability of occurrence while accounting for climate variability. The influence of climate variability on flood estimates in the region was linked to the Madden-Julian Oscillation (MJO) climate indices and resulted in increased flood magnitude for regional and direct flood frequency estimates varying from 0% - 35% and demonstrate that multi-decadal changes in atmospheric conditions influence both small and large floods. The results reveal the value of considering climate variability for flood frequency analysis, especially when non-stationarity is established by homogeneity analysis.
基金Supported by the National Key Basic Research Program of China under Grant No.2004CB418300National Natural Science Foundation of China under Grant No.40675042
文摘The flood and drought across the Yangtze and Huaihe River（Jianghuai） areas are frequent in summer, especially in June and July.Therefore,predicting the summer flood and drought in the Jianghuai region is always one of the key topics concerned by meteorologists in China.Previous studies focused more on the skin temperature anomalies in a local area,and paid less attention to the connections between the anomalies of land-sea thermal contrast in remote continents and the summer flood and drought in Jianghuai areas of China.By using the US NCEP/NCAR monthly mean reanalysis data and the rainfall data at 743 stations in China,based on the interdecadal variation characteristics of the flood and drought index（FDI） during 51 yr （1954-2004） in the Jianghuai region of China in summer,the North African areas have been selected as the key regions for the correlation analysis.The results show that the surface temperature anomalies in the key regions have good continuity in winter,and the winter North Atlantic Oscillation（NAO） is perhaps one of the important factors that bring about the continuity of the anomalies.By a singular value decomposition（SVD） analysis between the skin temperature in the previous winter in North Africa and the summer rainfall in the Jianghuai region,it is found that when the North African continent is colder（warmer） and its northwestern sea is warmer（colder）,the rainfall increases（decreases） in the Jianghuai region in summer generally.Further analysis finds that the anomaly of the surface temperature contrast between sea and land in North Africa has a good indication for the summer flood and drought in the Jianghuai areas of China.Therefore,a sea and land thermal contrast index（SLTCI） is defined to reflect the intensity of the large-scale land-sea thermal contrast.A positive correlation between the SLTCI in North Africa and the summer FDI in Jianghuai areas is identified,and it can well indicate the extreme flood and drought situations in the Jianghuai region of China.
