Observational Comparison of Two Torrential Rainfall Events in Beijing

In this paper, the two torrential rain processes in Beijing on July 21, 2012 (hereinafter referred to as “7.21”) and July 20, 2016 (hereinafter referred to as “7.20”) are analyzed to compare and reveal their differences from multiple perspectives using multisource observation and reanalysis data combined with various analysis methods. The results show that the total amount of precipitation for the two processes is similar, but the precipitation duration and hourly rainfall intensity are different, indicating that the duration of “7.21” is shorter and the rainfall intensity is stronger, which corresponds to the dominant weather system and evolution, convective system evolution and local sounding conditions of the two processes. The convective effective potential energy is significant in “7.21” main precipitation period resulting in the dominant convective heavy precipitation in a warm area, whereas the convective effective potential energy is small in “ 7.20” main precipitation period and is dominated by low vortex systematic precipitation. Therefore, significant differences are observed in the statistics of hourly rainfall intensity and short-duration rainfall events between the two processes. The proportion of medium intensity hourly rainfall stations of “7.20” is significant, whereas the proportion of short-duration heavy rainfall stations “7.21” is obvious. The differences in accumulated rainfall, duration, 5 min, and 1 h maximum rainfall between the two short-duration precipitation events are significant. The “7.21” short-duration heavy rainfall events (the short-duration extremely heavy rainfall events with an hourly rainfall of more than 50 mm accounted for a significant proportion) exceeded half, as well as the maximum 5 min and 1 h precipitation were 20.4 and 103.6 mm, respectively. While the short-duration medium intensity precipitation events of “7.20” accounted for the largest proportion, the maximum 5 min and 1 h precipitation of only 10.7 and 59.3 mm. Compared with “7.20”, “7.21” is more disastrous. The contribution of water vapor from central and eastern China as well as coastal areas is the largest in both processes, with “7.21” being more pronounced. However, the contributions of the Indian Peninsula–Bay of Bengal–Central South Peninsula, South China Sea, Northwest Pacific, and the Sea of Japan are also obvious in the “7.20”. The above conclusions contribute to understanding the reasons for the different disasters of the two torrential rain processes.