Abstract:

Using the daily 08-08 precipitation data of 56 national weather stations in the middle and lower reaches of the Jinsha River Basin from 2000 to 2012, the daily areal rainfall of the five subbasins is calculated by an arithmetic average method. The spatial and temporal characteristics of the areal rainfall in the middle and lower reaches of the Jinsha River basin and its five subbasins were analyzed, focusing on the analysis of the statistic characteristics such as seasonal distribution, frequency distribution, grade distribution, extreme value distribution of the days of heavy daily area rainfall. The results show a great temporalspatial variation of precipitation in the middle and lower reaches of the Jinsha River basin. The annual areal rainfall varied between 600 and 980 mm and averaged 812 mm. The highest annual average areal rainfall was found in  HuatanPingshan subbasin (876 mm) and the lowest value was found in the subbasin of the lower reaches of the Yalong River (723 mm). The precipitation peaked in summer, followed by autumn, spring and winter. The precipitation was concentrated from May to October, contributing 91% to the total. The frequency of heavy precipitation shows obvious seasonality: highest in summer  followed by autumn and zero was found in winter. Days with heavy precipitation of above 20 mm in the five river subbasins in thirteen years was 383 in total, averaged 29.5 days per year. The frequency of heavy precipitation was at most in HuatanPingshan subbasin, followed by Hengjiang River subbasin and the lowest was found in the subbasin of the lower reaches of the Yalong River. The heavy precipitation was concentrated from June to September, with a total of 340 mm, accounting for 88.8% of the whole year. The heavy precipitation between 30 mm and 50 mm was concentrated on the HuatanPingshan and Hengjiang River subbasins, and heavy precipitation exceeding 50 mm was concentrated on the Hengjiang River subbasin. The monthly maximum of Hengjiang River subbasin was greater than else and the subbasin of the lower reaches of the Yalong River was significantly smaller than else in the period of heavy precipitation. The highest frequency of simultaneous heavy precipitation was found in HuatanPingshan and Hengjiang River subbasin, counting for 52.1% of the total. This phenomenon should receive attention for areal rainfall forecast