关键词: 降水结构, 汛期, 降水历时, 降水等级, 北江流域

Abstract:

Although precipitation in the Beijiang River Basin has been discussed in many previously conducted studies, precipitation structure has been rarely investigated. Therefore, this study analyzes the spatial-temporal variation characteristics of precipitation structure in the rainy season (from March to August) using 50 years of daily precipitation data for the Beijiang River Basin. The precipitation duration and precipitation grade are specifically addressed using the precipitation incidence rate and precipitation contribution rate indexes.The results show that 1) the precipitation incidence rate decreases exponentially with an increase in the precipitation duration and increases with an increase in the precipitation grade. As the precipitation duration increases, the precipitation contribution rate initially increases and then decreases. 2) The spatial difference of incidence rate for different durations appears as a local high or low spatial difference (island distribution) for durations of 1-2 days and≥10 days. The spatial difference of contribution rate for different durations can be observed as a reverse change in the north and southeast directions that appear at durations of 2-4 days and≥10 days. 3) Regionally, the incidence rate of the events graded as light rain and torrential rain were mainly reflected in the reverse changes in the north (including Lechang, Shixing, and Nanxiong) and the southeast (including Fogang, Qingyuan, and Yingde). The contribution rate of heavy rain was high in the west, and the contribution rate of torrential rain in Qingyuan and Fogang in the southeast was about 39%, making the torrential rain center in Beijiang river basin. 4) Short and medium duration events (1-6 days) did not significantly decrease, and the contribution rate did not significantly increase. However, the incidence and contribution rates for long duration events (≥7 days) decreased. No change was observed across all the precipitation grades; the incidence and contribution rate of light rain and moderate rain did not significantly decrease, whereas the incidence and contribution rate of heavy rain and torrential rain did not significantly increase. 5) The relative locations of land and sea (which affected the continuous water vapor supply) and differences in topography (which affected the moving path and speed of the weather system) were important factors that affected the spatial difference of the precipitation structure. The background of global warming also affected the regional precipitation structure change trends.To completely understand the specific physical mechanism associated with the precipitation structure changes, further study into large-scale circulation and the underlying dynamic influence mechanisms is advised. However, this study provides a scientific basis to guide regional production activity and disaster prevention as well as reduction construction.

Key words: precipitation structure, rainy season, precipitation duration, precipitation grade, Beijiang River Basin