山东省近50年来降水事件变化特征

基于1951—2017年淮河流域及其周边68个气象站的年暴雨日数和年最大日降水量数据，采用经验模态分解方法分析暴雨频率和强度的平均趋势和周期，采用Copulas函数分析暴雨的综合危险度及重现期，探讨淮河流域暴雨危险度的时空变化特征。结果表明：(1) 流域暴雨频次呈现先降后升趋势，转折点在1980年左右；暴雨强度则一直呈显著的线性上升趋势。暴雨频率和强度的主周期均为准2 a。(2) 全流域90 % 以上的暴雨频次在3 d及以内，且暴雨强度小于100 mm。暴雨频率和强度超过该阈值后，增加显著变缓。暴雨重现期值随两单指标值的增加而增大，且增大速率逐步变快。(3) 暴雨频次和强度的平均变化趋势的高值在空间格局上基本一致，且两指标升降趋势的面积比相当。(4) 流域暴雨危险度联合概率的均值和最小值空间格局基本一致，最大值分布则比较分散。流域西北部的部分区域虽然暴雨频次和强度呈现下降趋势，但联合概率估计的暴雨危险度均值和最小值却很高。

The empirical mode decomposition and the Hilbert spectrum for non-linear and non-stationary time series analysis

To explore the temporal and spatial characteristics of the torrential rain in Huaihe River basin,this article analyzed the average trend and period of the rainstorm frequency and intensity by the empirical mode decomposition method,and then analyzed the comprehensive danger and return period by the Copulas function based on the torrential rain days and maximum daily precipitation data for each year at 68 meteorological stations from 1951 to 2017. The results are as follows. (1) The rainstorm frequency of the whole basin firstly decreased and then increased in the study period,and the turning point occurred around 1980. The intensity has been showing a significant linear upward trend. The main periods of rainstorm frequency and intensity are both subject to 2 a. (2) For more than 90% of the torrential rain,the frequency is 3 days or less and the intensity is less than 100 mm. The increasing rate slows down significantly when exceeding these thresholds. The return period of torrential rain increases with the two single indexes increasing,and the rate gets faster gradually. (3) The high values of the spatial pattern of the average change trend for the two indicators are consistent. And the area ratios of the rising and falling trends of the two indicators are similar. (4) The spatial pattern of the mean and minimum values of the joint probability of the rainstorm is consistent,while the distribution of its maximum values is relatively dispersed. Although the frequency and intensity of rainstorms in some cities show downward trends,the mean and minimum values of the danger of the rainstorm hazard evaluated by joint probability are very high.