Temporal And Spatial Evolution Characteristics Of Rainfall Erosivity Under Different Rainfall Levels In Chongqing

The complex topography and abundant rainfall have caused the upper reaches of the Yangtze River to become one of the areas with the most serious soil erosion in China.Chongqing is an ecological barrier in the upper reaches of the Yangtze River and the main location of the Three Gorges Reservoir.The severe soil erosion in Chongqing will pose a serious threat to the ecological environment to the lower reaches of the Yangtze River and the Three Gorges Reservoir.Rainfall erosivity represents the potential of soil erosion.Studying the temporal and spatial variation characteristics of rainfall erosivity of different rainfall levels is of great significance for predicting the degree of soil erosion and proposing measurements for soil and water conservation.At present,many scholars have studied the construction of a simple model of rainfall erosivity and the temporal and spatial distribution characteristics of rainfall erosivity in Chongqing,but there are few studies on the temporal and spatial variation characteristics of rainfall erosivity under different rainfall levels.In this paper,we collected daily precipitation data from 1960 to 2017 of42 meteorological stations in Chongqing and surrounding areas,and analyzed the temporal and spatial distribution characteristics of rainfall,the number of rainfall days,erosive rainfall and the number of erosive rainfall days.A calculation model of precipitation erosion based on daily rainfall was used to calculate rainfall erosivity.Mann-Kendall Test methods,cumulative anomaly methods,and sliding t-test methods were used to investigate temporal and spatial variations in rainfall erosion of various sizes which will provide criteria for the prevention and control of soil erosion in Chongqing.The main results are as follows:(1)By comparing the annual variation and the distribution within year of the number of days of rainfall,rainfall,erosive rainfall,and erosiveness in Chongqing,we can see that the erosiveness is mainly caused by a rainfall event with a small number of rainfall days but a large amount of rainfall.The number of rainfall days in each season is similar;while the number of erosive rainfall days,rainfall,erosive rainfall and rainfall erosivity are significantly higher in summer than in other seasons.The number of rainy days in each month accounted for a relatively uniform proportion of the year.The number of erosive rain days,rainfall,erosive rainfall and rainfall erosivity accounted for the number of annual rainfall days,rainfall and rainfall erosivity respectively.May to September are higher,but the highest ratio appears in different months.The annual rainfall erosivity in Chongqing is high in the southeast and northeast,and low in the west.The maximum annual rainfall erosivity appears in the Youyang area in the southeast.(2)From the annual scale,the annual rainfall erosivity is mainly caused by the rainfall erosivity of heavy rain and higher rain level.The increase of the erosivity of the heavy rain plays a leading role in the increase of the erosivity of the annual rainfall.The erosivity of moderate rain and the erosive force of heavy rain had abrupt changes in 2013 and 1975,respectively.From a seasonal perspective,summer rainfall erosivity is dominant in annual rainfall erosivity,while winter rainfall erosivity does not contribute much to annual rainfall erosivity.The increase in erosivity of large storm increases the risk of soil erosion in spring,and the increase of erosivity of heavy rain leads to the increase of erosivity of summer rainfall.Rainfall erosivity in fall and winter all shows a downward trend.On a monthly scale,the highest rainfall erosivity in July caused the highest risk of soil erosion.The high values of rainfall erosivity of different rainfall levels mainly appear from May to September.The rainfall erosivity of different rainfall levels in June shows an upward trend,and the erosivity of large storm has a significant upward trend.(3)From an annual scale,the annual rainfall erosivity,moderate rain erosivity,and heavy rain erosivity present the spatial distribution characteristics of high in the east and low in the west,while the spatial distribution of erosivity of storm and large storm is the highest in the western mountainous area of the northeast.On a seasonal scale,the spatial distribution pattern of rainfall erosivity of different rainfall levels in spring,autumn,and winter is roughly the same as that of total rainfall erosivity in spring,autumn and winter in Chongqing,but the spatial distribution of rainfall erosivity of different rainfall levels in summer is very different.On a monthly scale,the area with high monthly rainfall erosivity appears in the southeast from May to June,and in the northeast from July to September;however,the spatial distribution of rainfall erosivity of different rainfall levels varies greatly from month to month.There are obvious spatial differences in the changing trends of rainfall erosivity of different rainfall levels on different time scales.This study analyzed the temporal and spatial evolution characteristics of rainfall erosivity of different rainfall levels on different time scales,clarified the composition structure of rainfall erosivity in Chongqing,and clarified the periods and regions with high probability of soil erosion,which can provide reference for the prediction,early warning and evaluation of soil erosion risk in Chongqing and the Three Gorges Reservoir area,as well as for the formulation of prevention and control measures in key soil erosion control areas.