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.