基于灾情信息的1981—2017年北京地区降雹特征

该文对1981—2017年北京地区1010个高精度冰雹灾情信息进行统计分析。从年代际变化看，1981—1990年平均降雹日数为10 d，1991—2000年和2001—2010年年平均降雹日数均有所减少（5.67 d和4.33 d），而从2011年起，年平均降雹日数急剧增加到21 d。1981—1995年年平均最大冰雹直径总体呈增加趋势，2002年开始总体较小。从年变化看，冰雹日数的年变化呈明显的单峰型即初夏峰型，4月起降雹日数逐渐增加并在6月达到峰值，其后缓慢下降。从空间分布看，北京地区的降雹分布十分广泛，但高频次降雹区域主要集中在北京西北部延庆区，平均每年至少发生两次降雹，此外降雹高值区还出现在城区的海淀区。2010年后，降雹范围明显增大，同时降雹分布也由相对集中变为相对均匀。

Characteristics of Hailstone Distribution Based on Disaster Information in Beijing from 1981 to 2017

Fine analysis on the variation of temporal and spatial distributions of hail day, frequency and size is very important for risk evaluation and hail suppression. The hailstone disaster information with high spatial resolution can be used to provide database for analyzing characteristics and patterns of hail distribution. After meshing the hailstone disaster information in Beijing into a gridded database, the following results are summarized by analyzing 1010 cases of hail disaster information in Beijing during 1981-2017. The number of annual averaged hail days during 1981-1990 is 10 days, which is relatively more than that during 1991-2000 and 2001-2010, while the number increases to 21 days from 2011 to 2017. The annual averaged maximum hail diameter increases from 1981 to 1995, and then decreases since 2002. It is significant that the monthly variation of hail days is unimodal distributed. Hail days increase gradually from April and reach the peak in June, and then decline slowly. The average monthly hail days during 2011-2017 are higher than those in other periods, and the average monthly hail days during 2001-2010 are generally low. The difference of maximum hail diameter in each month is not obvious, as far as the difference between different ages, the monthly maximum hail diameter during 1981-1990 increased first and then decreased, while the value during 1991-2000 is larger in general. Hails occur most frequently in the afternoon in Beijing. The daily variation of hail days during 1981-1990 and 1991-2000 show obvious single peak characteristics, but the frequency drops significantly from 2001 to 2010. The frequency of hails from 1400 BT to 2100 BT during 2011-2017 is stable and much higher than that in 1991-2000 and 2001-2010. At the same time, it is also observed that hails occurring at night during 2011-2017 are also higher. It is obvious that hailstorms are widely distributed in Beijing. The maximum hail frequency of horizontal distribution is the highest in 1981-1990, and then decreases gradually, but recovers during 2011-2017. During 1981-1990 and 2001-2010, the hail frequency in Yanqing District, northwest of Beijing is the highest, and Haidian District is another high hail frequency area in Beijing downtown. From 2011 to 2017, the distribution of hailstorms is relatively uniform. Combining the information of hail disaster with other related data, and causes for this spatial and temporal distribution variation will be investigated.