近40年北京地区夏季降水日变化及不同持续时间降水事件的特征

利用北京地区20个国家站1980～2020年的长期逐时降水资料，分析了北京夏季降水的基本气候特征和日变化时空分布特征。结果表明:（1）北京地区夏季40年平均降水量分布具有西北山区小，平原大，山区向平原过渡区的迎风坡最大的特点；降水频率则相反，平原降水频率整体小于山区；降水强度整体表现为西北弱，东部强，城区与南部居中的特点。北京夏季降水的强度和极端性较强，致灾风险高。（2）北京夏季平均降水量日变化主体呈单峰型，降水频次为双峰型，降水强度为多峰型，三者同时在22时（北京时，下同）达到最大，在12时最小。（3）降水的峰值时间随月份依次后推，6月最早，7月次之，8月最晚；峰值雨量7月最大，8月次之，6月最小。（4）降水量、降水频率和降水强度的日峰值空间分布具有较强的一致性，西北山区四站出现在20时以前，其余16站出现在20时及以后。使用K均值聚类算法将20站划分为两个区域，结果显示两个区域的降水量、降水频率和强度的日变化具有完全不同的分布特点。（5）近40年北京地区的降水结构在不断调整，短持续时间降水主导期和长持续时间降水主导期交替出现。2000年以前以小于6小时的短持续性降水为主，近15年大于6小时的长持续性降水明显增多。

Diurnal Variation Characteristics of Summer Precipitation and Precipitation Events with Different Durations in Beijing in the Past 40 Years

Using the long-term hourly precipitation data of 20 national stations in Beijing in the past 40 years, this study investigates the temporal and spatial distribution characteristics of the diurnal variation of summer precipitation in Beijing. Results show that (1) the precipitation amount is small in the northwest mountainous area and large in the plain, and the slope in the transition area from the mountainous area to the plain is the largest. In contrast, the precipitation frequency in the plain is less than that in the mountainous area. The precipitation intensity is weak in the northwest and strong in the east. The intensity and extremes of summer precipitation in Beijing are strong, and the risk of disaster is high. (2) The diurnal variation of precipitation amount in summer in Beijing is a single-peak type, the precipitation frequency is a double-peak type, and the precipitation intensity is a multi-peak type. These values reach the maximum at 2200 BJT (Beijing time) and the minimum at 1200 BJT. (3) The peak time of precipitation varies with the month, the earliest in June, the second earliest in July, and the latest in August. The peak precipitation amount is the largest in July, the second largest in August, and the smallest in June. (4) The spatial distributions of the peak precipitation amount, peak precipitation frequency, and peak precipitation intensity exhibit strong consistency. They appear before 2000 BJT in the northwest mountainous area and after 2000 BJT at the other 16 stations. Using the K-means clustering algorithm, the 20 stations are divided into two regions. The results further show that the diurnal variation of precipitation amount, precipitation frequency, and precipitation intensity in the two regions have completely different distribution characteristics. (5) In the past 40 years, the precipitation structure in Beijing has been continuously adjusted, and the short-duration and long-duration precipitation dominant periods appear alternately. Short-duration precipitation within 6 h dominated before 2000, whereas long-duration precipitation greater than 6 h increased significantly in the past 15 years.