Abstract:

Against the backdrop of global warming, the structure and patterns of precipitation have changed significantly. This includes changes in the non-uniformity of spatial and temporal distribution of precipitation, while the frequency of extreme precipitation events has increased. Studies have shown that regional drought and flood disasters are related to rainfall and also closely related to the frequency and intensity of precipitation. As the main climate factor, the spatial and temporal variation in precipitation for different grades has become of significant research interest in recent years. Based on daily precipitation data from 1960 to 2017, this study used the Mann-Kendall non-parametric test and R/S analysis (rescaled range analysis) to analyze characteristics of spatial-temporal variation for precipitation at different grades in the Taihu Lake Basin for the past 60 years. Additionally, these results were used to explore the impacts of this variation on the annual precipitation. The observed daily precipitation (P) was categorized into four grades of intensity: light precipitation (0.1≤P<10 mm/d); moderate precipitation (10 ≤P<25 mm/d); heavy precipitation (25≤ P<50 mm/d); and storm precipitation (P≥ 50 mm/d). These classification criteria have been used in many global precipitation analyses. The results show that the annual precipitation days were dominated by light rain days, accounting for 73.55% of the total annual precipitation days between 1960 and 2017. The contribution rate of light rainy days to the total annual precipitation days had significantly reduced, and the contribution rate of heavy rainfall to the total annual rainfall had significantly increased. There was a significant increase in the rainfall, rainy days of heavy and storm rain, rainfall intensities for light rain, and the annual average precipitation. The number of light rain days had decreased significantly, and the precipitation structure in the Taihu Lake basin showed a tendency to shift to extreme heavy precipitation. There were significant differences in the spatial distribution of precipitation trends for different grades. The light rainy days, total annual precipitation days, and intensities of light rain and annual average precipitation showed a similar spatial pattern in the changing trend. The light rainy days and total annual precipitation days showed a significant downward trend across the entire basin, while the intensities of light rain and annual average precipitation showed a significant increasing trend. The spatial distribution of the change in the days of moderate rain, heavy rain, and storm rain were similar to the corresponding spatial pattern of rainfall. R/S analysis showed that, in addition to light rainfall, the indicators related to light rain, heavy rain, and annual total precipitation showed strong persistence, and the future trend was consistent with that of the past. In the past 60 years, the annual total rainfall, precipitation days, and annual average precipitation intensity in the Taihu Lake basin were greatly affected by moderate rainfall, light rain days, and heavy rainfall, respectively. The annual precipitation reduction was greatly affected by the decrease in heavy rainfall in dry years, and the increase in annual precipitation was heavily impacted by the increase in storm rainfall in flood years. There is a need for further study on the climate dynamic mechanisms underpinning different precipitation grades, such as atmospheric circulation and water vapor transport.

Key words: rainfalls, precipitation days, precipitation intensity, spatio-temporal variation, Taihu Lake Basin