| Based on the daily maximum temperature, daily minimum temperature, precipitation and other meteorological data of 23 typical cities in the eastern monsoon region of China, and combined with the detailed city waterlogging data reported by recent media. In this paper, the methods of linear trend analysis, percentile threshold method and Arcgis spatial analysis are used to explore the extreme climate events and urban waterlogging in the eastern monsoon region typical cities of China. The results are as follows:1. Through the time trend analysis of the cold event indicators in the study area, we can see that the changes of cold event indicators showed a trend of decrease overall in most cities. Visible, affected by global warming, most urban climate of monsoon region of eastern China has a tendency to warm. From the point of spatial distribution characteristics, due to the differences of latitude city receives solar radiation heat, the annual average of frost days showed decreasing pattern mainly from high latitudes to lower latitudes. Among them, frost days in the northeastern region were the longest, while the southeast coastal areas shortest. The variation annual average of the cold continuous index showed a distribution pattern that northeast, southwest more, central and southeast fewer. The cold duration index were higher to the north of Beijing and the entire northeast region, and relatively low in central and southeastern cities, especially in the subtropical monsoon climate zone, the cold duration index were lower. Distribution patterns of the annual average cold night days showed that northeast and south high, east and southwest low. In addition, through the analysis of the annual maximum cold event index we can see that, the maximum frost days were reduced gradually from the northeast to southwest. Bounded by the Yellow River basin, frost days were higher in the North, while the south Basin area is relatively small, especially in the southern coastal area, the frost days were less. The high value area of annual maximum cold continuous index were mainly in North China and Sichuan Basin, southwest and south area the cold continuous index were relatively low. Similarly, gap of regional about cold night days is large.Simultaneously, both the high value city and low value city distributed in the same region. Visible, the distribution pattern of cold night days in the eastern monsoon region of our country, is the result of interaction of various meteorological factors. In addition, the regional difference of annual maximum cold days is large. The high value mainly concentrated in Southern and East China, low value distribution is relatively dispersed.2. By the time trend analysis of the warming events in the study area that, extreme warm events in Eastern China monsoon region presented a increasing trend of different level. It can be said that by the impact of global warming, the climate in the study area showed a warming trend. From the point of view of spatial distribution characteristics, to the various average indicators, because of the different solar radiation heat gain in different latitude city, summer days average distribution is roughly as follows:low latitude city summer days longer, and shorter in high latitude city. The regional distribution of hot continuous index is obvious, high value is mainly concentrated in the eastern and central regions, low value mainly in the north, northeast and southwest China. But the relatively low value of warm night days average mainly concentrated in the southeast coastal areas, and the high value mainly concentrated in the north and southwest China. In terms of the warm days, in the south of the Yangtze river which is greatly influenced by the summer monsoon region,the warm days were relatively few. While in the less affected northern region, warm days were more, and the regional difference was small. In addition, the analysis of maximum warm event indicators showed that, the maximum summer days distribution has obvious latitude zonal characteristics, the summer days in each city distribution mainly high-latitude shorter, low-latitude longer, in addition to the southwest and parts of the inland city, and the regional difference is obvious. And the high level of hot continuous index maximum mainly concentrated in the eastern and central regions, the lower is mainly in the northeast and southwest area. Warm night days maximum high cities are mainly distributed in the region south of the Yangtze river basin, the north of basin numerical is relatively small. Warm days in low latitude area distribution long, but short in high latitude regions, this distribution pattern is directly related to the heat radiation of the city acquired.3. Study on continuous dry wet events, from the time change trend that, in addition to the southwest, the vast majority of the eastern monsoon region city continued dry index tended to decrease,which reflects the climate change from dry to wet in the study area. In contrast, the change range of continuous wet index in the study area is small. The spatial distribution characteristic of average more each index showed that: Influenced by the southeast monsoon, sustained higher dry index value in the study area mainly concentrated in the north of the Yellow River, while low value mainly concentrated in south, and the regional difference is bigger. The distribution of high value continuous moisture index were located in the south of the Yangtze where summer monsoon affects obvious, low value were in the north. From the point of view of the distribution characteristics of maximum value of each index in space.There is a direct relationship between the distribution about the continued dry index and the degree of summer monsoon influence in the study area. Apart from a few cities, high value of continued dry index mainly distributed in the northern region, while the southern region value is relatively low, also, the regional difference is bigger. Instead, sustained high wetness index value cities are mainly distributed in the southeast monsoon far-reaching south, especially in the southeast coastal area. Northern cities, by contrast, many scattered wetness index are lower.4. Through the time trend analysis of the heavy rain events in the study area, we can see that the change of 5 day maximum precipitation showed a trend of decrease in most cities, only a few cities distributed in central and southeast coastal area showed an increasing trend. For daily precipitation intensity, the magnitude of change is small in the study area cities. But the rainfall intensity increased in most cities and they mainly distributed in the south of the Yellow River. And the trend of strong precipitation days and extreme strong precipitation days were not obvious increasing in majority cities. Relatively, affected by global warming, the southeast monsoon forces strengthened. Strong precipitation and extreme strong precipitation in most cities in eastern monsoon China showed a significant increasing trend. From the point of the space distribution features,by analysis of the average value about each indicator that, the distribution of 5 day continuous maximum precipitation in the study area is significantly affected by the southeast monsoon, the high value of precipitation is mainly concentrated in the south of Yangtze River, and low value in the north. Similarly, precipitation intensity high value city mainly distributed in the southeast coastal area where summer monsoon effect obviously, and low-value cities are mainly distributed in northeast and inland areas,also, the region difference is more apparent. Affected by the monsoon, the average of precipitation days,extreme precipitation days, strong precipitation and extreme precipitation distribution similarity in the eastern monsoon region, each index of high value city mainly concentrated in the south of the Yangtze river area, and low city mainly concentrated in the north region where the summer monsoon affects poorer, especially in north China. Furthermore, the analysis results of various index maximum showed that:Because of the impact of the summer monsoon, the maximum value of 5 consecutive daily precipitation in the monsoon region of eastern China distribution more in the southeast, few in the northeast and inland, and the regional difference is obvious. Distribution characteristics of precipitation in North China and Shandong region is high, northeast and southwest low, regional differences are also obvious. Followed, the distribution of precipitation days, extreme precipitation days and the strong precipitation distribution more in the south than in the north. The extreme precipitation is different, the high value are mainly distributed in the North China and Southern China region, other regions less. In short, there is a direct relationship between the spatial distribution characteristics of rainfall events and the effect of the summer monsoon, more heavy rain events happened in the summer monsoon influence strong area.5. In recent years, our country’s urbanization advancement speeding up unceasingly, increasingly extreme precipitation events lead to urban rainstorm waterlogging disasters occurred frequently. From the point of the time characteristics of urban waterlogging, the total number of urban waterlogging event in eastern monsoon region has increased every year, with an average growth rate of 49.685 times/10a. Affected by the summer monsoon, different grades of waterlogging occur most frequently in July in the study area. From the point of view of spatial distribution characteristics, different risk level of the frequency of urban waterlogging in the south was obviously higher than in the north, and the regional difference is large. Rainstorm waterlogging occurred more in Guangzhou and Beijing, but Kunming and Guiyang less. Through the analysis of the causes of waterlogging, the key factor that lead to urban waterlogging is the growing number of extreme heavy precipitation event which under the influence of global climate change. In addition, also related with the city geography and infrastructure. Affected by global warming, most cities’ climate of the research area tend to be warmer and wetter. An increase in warm-wet events will promote regional precipitation events. As a result, the number of rainstorm waterlogging events in the study area is likely to increase, and bring greater disaster losses to the eastern monsoon region typical cities in China. In response, we should strengthen the cities’ early warning and forecasting of extreme precipitation, so that achieves accurately forecast, early prevention. We should also attach great importance to the urban infrastructure, good overall planning the urban flood control and drainage system. Finally, we should be appropriate drawing on the successful experience of domestic and foreign urban rainstorm waterlogging prevention, to establish effective mechanism by rainstorm waterlogging and drainage system of GIS database, in response to the flooding and ensure the safety of our city. |
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