The temporal and spatial distribution characteristics of rainstorm areal rainfall over Xijiang river basin in the past 45 years

Using daily precipitation data at 122 meteorological stations from 1971 to 2015, the Tyson polygon method was used to calculate the daily rainfall in 22 sub-watersheds in the Xijiang river basin. The temporal-spatial distribution characteristics and its mutation characteristics of the ten-day average rainstorm areal rainfall, torrential rain days and the rainfall intensity were investigated by means of synthetic analysis, trend analysis and Mann Kendall method. The results indicate that (1)the rainstorm areal rainfall, torrential rain days and the rainfall intensity in the Xijiang river basin showed a similar spatial distribution in the past 45 years, which was larger in the eastern Xijiang river basin than in the west. The maximum value was in the eastern part of sub-watersheds, and the minimum value was in the western sub-watersheds. The rainstorm areal rainfall and the torrential rain days were larger in pre-flood season than in late flood season, while the rainstorm intensity was stronger in mid-late flood season than in pre-flood season. The torrential rain days first appeared in the east-northern part of Xijiang river basin, and first ended in west. The heavy rainstorm area first appeared in the eastern part of Xijiang river basin, and first ended in southwest. (2) The ten-day rainstorm areal rainfall and the torrential rain days showed a single peak distribution, with the peak and sub-peak in early to middle of June. However, the trend of rainstorm intensity showed a fluctuation, with the weakest in early April and the strongest in mid-June. (3) In the past 45 years, the rainstorm areal rainfall, torrential rain days and the rainfall intensity showed an increasing trend, especially for the rainfall intensity. But a significant mutation occurred in 1992. After the mutation, the mid-eastern sub-watersheds were increased (or enhanced), part of the western, southern and northern sub-watersheds were reduced (or weakened).