降水时间随机性对月总降水量的影响

降水量在时间分布上呈现较大的随机性,极端降水事件尤为如此。受此影响,月初(月末) 1～5 d之内的累积降水量很可能会超过当月总降水量的50%乃至更多。对1961—2017年中国2 400多站点资料统计分析结果发现,月初(月末) 1～5 d累积降水量对当月总降水量显著影响事件的出现频次,在季节和空间分布上都有鲜明特征。主要包括:1)月初累积降水量对秋冬季中各月的总降水量影响更大,月末累积降水量对1—4月的月总降水量影响较大。2)受月初累积降水量的影响,显著站点数在某些年份的某些月份出现极大值;受单次事件显著影响的站点数占全国总站点数的30%～50%,此即对应着一次全国大范围的极端降水事件。3)受月初(月末)累积降水量显著影响的站点空间分布随季节变化呈现出明显空间集聚特征。

The influence of temporally-random precipitation on monthly total precipitation

Due to the random nature of precipitation events,the accumulated precipitation within the first (final) 1-5 days of a given month is likely to exceed 50% or more of the total precipitation in that month.Using the daily rainfall data from more than 2 400 stations in China from the period of 1961 to 2017,the statistical analyses in this paper show that such events occur with significant features in both the seasonal and spatial distribution:1)The cumulative precipitation in the first 1-5 days can influence the monthly precipitation during the fall and winter,and the cumulative precipitation in the final several days can influence the monthly precipitation during the period of January to April.2) The number of stations significantly affected by accumulated precipitation of the first several days has a maximum value in some years and months.The number of stations significantly affected by such event reaches about 30-50% of the total number,which corresponds to a large-space extreme heavy precipitation event.3) The stations significantly affected by such events show features of spatial concentration in September.For example,the stations affected by the first 5 days of September are mainly concentrated around Shandong and Hebei Provinces,and such events in those regions have occurred about 20 times during the past 57 years.