Analysis on the characteristics of hourly precipitation variations in Beijing-Tianjin-Hebei region during 1970-2015

Using the daily and hourly precipitation data at 28 national automatic weather stations over Beijing-Tianjin-Hebei region in warm season between May and September during 1970-2015, we have analyzed the variation trend and the daily variation characteristics of precipitation. The results show that the trend of total precipitation amount and extreme precipitation at most of the stations have increased weakly in prophase (May and June), decreased evidently in metaphase (July and August), and increased evidently in telophase (September). Also, it is found that most of the stations locating in west part of Beijing-Tianjin-Hebei region show increasing trends of total precipitation amount and extreme precipitation, while a few stations locating in northeast part have decreasing trends in prophase. And most of the stations have decreasing trends in metaphase, especially those locating in northwest part. However, almost all of the stations have increasing trends in telophase. The following are the main characteristics of the daily variations of monthly precipitation in warm season. The long-duration rainfall events that last longer than 6 hours occur frequently in the late night to early morning, while the short duration rainfall events of 1-6 hours in duration mainly occurs in the afternoon to evening and is affected by monthly temperature changes. Short duration rainfall events in afternoon weaken in prophase, increase in metaphase and weaken again in telophase. In prophase of warm season, short duration rainfall events in afternoon, that is more related to convective precipitation, increases in frequency, which is advantageous to strengthening of hourly extreme precipitation. In metaphase of warm season, nocturnal accumulated precipitation has decreased significantly since 1997. The decrease of precipitation amount of short duration rainfall events in afternoon is mainly caused by the decrease of precipitation events. However, precipitation amount in telophase of warm season has increased significantly since early 2000s. The intensity and frequency of long-duration precipitation events increased at night to early morning, in which rainfall increment due to precipitation intensity contributes more to precipitation increase.