Changing properties of precipitation extremes in the urban areas, Yangtze River Delta, China, during 1957-2013

摘要

The Yangtze River Delta (YRD) is one of largest river deltas and metropolitan areas in the world with strong human interference, so it is vulnerable to extreme weather events. Based on daily precipitation dataset of 16 rain gauges in Yangtze River Delta and Mann-Kendall trend detection techniques, the trend in annual and seasonal precipitation extremes has been investigated in the period 1957-2013. Possible links between changes in extreme precipitation and monsoon indices have also been explored. The results show that: (1) the increasing trends of consecutive wet days, maximum daily precipitation, maximum 5-day precipitation and maximum precipitation amount in the past 57 years in YRD can be detected. Much attention should be paid to higher risk of flash flood in these areas, especially in big cities of Shanghai, Nanjing, Hangzhou and Ningbo. (2) Both precipitation days and amount of heavy events (defined as over 90th, 95th and 99th) exhibit overwhelming upward tendency in summer and winter throughout YRD. The summer is to meet with heavier precipitation events as result of larger increasing magnitude in heavy rain days and amounts in the past 57 years. So, high importance should be placed on the relief for flood in summer in the large cites. (3) There is an abrupt change point for extreme precipitation events, and increased annual total precipitation has impact on the upward tendency of heavy rainfall events in YRD on great scale. In addition, the significant correlations between indices (P90, P95, R90 and R95) and monsoon indices (East Asian Summer Monsoon Index and South Asia Summer Monsoon Index) indicate that extreme precipitation events are related to the EASMI and SASMI. Therefore, these properties of precipitation extremes are of great significance to the control of natural hazards in YRD with high degree of human activities and understanding the impact of climate change on hydrologic processes.