Objective partition of flood season precipitation and its spatio-temporal characteristics of diurnal variation in Guangxi

Based on hourly precipitation data from 91 national stations in Guangxi during the flood season from 2005 to 2022, the precipitation during the flood season in Guangxi was objectively divided into 5 regions by using the K-means clustering algorithm, including Region I in the northwest of Guangxi, Region II in the northeast of Guangxi, Region III in the southwest of Guangxi, Region IV in the southeast of Guangxi, and Region V along the coastal areas of southern Guangxi. The diurnal variation characteristics of precipitation during the pre- and post-flood seasons in various regions were analyzed. The results are as follows. (1) There is a significant difference in the daily variation of average precipitation in the entire region between the pre- and post-flood seasons. The pre-flood season shows a unimodal pattern with mainly nighttime precipitation, while the post-flood season shows a bimodal pattern with generally more daytime precipitation than nighttime precipitation. (2) There are regional differences in the diurnal variation characteristics of precipitation in the flood season. The precipitation and frequency in northwest and northeast Guangxi show a unimodal pattern during the pre-flood season, but change to a bimodal pattern during the post-flood season. Southwest and southeast Guangxi show a bimodal pattern during the pre- and post-flood seasons, while the coastal southern Guangxi shows a unimodal pattern during both periods. (3) With increasing precipitation duration, the cumulative precipitation first increases and then decreases. The contribution of short-duration precipitation processes is predominant during the day, while long-duration precipitation processes contribute more during the night. (4) The heavy precipitation from late night to early morning is attributed to the obvious water vapor convergence and strong convergent ascending motion, while the heavy precipitation from afternoon to evening is mainly attributed to abundant water vapor conditions and strong thermal forcing.