Simple Algorithm Of Rainfall Erosivity And Its Temporal And Spatial Distribution In Pingjiang Basin Of Jiangxi Province

Soil erosion can cause serious floods and droughts,which poses a great threat to the sustainable development of human society.The Pingjiang basin is located in the red soil region of the upper reaches of the Ganjiang river,which is highly prone to soil erosion.The stability of the upper reaches of the Ganjiang river directly affects the ecological stability and economic development of the middle and lower reaches of the Ganjiang river.Based on the precipitation process data of nine rainfall stations in the Pingjiang basin in the upper reaches of the Ganjiang river from 1989 to 2018 for 30 consecutive years,this paper compares the applicability of the simple rainfall erosivity algorithm in the study area and analyzes the erosive sub-rainfall.On the basis of this,a simple algorithm for calculating the monthly rainfall erosivity using daily rainfall is proposed.The temporal and spatial distribution of rainfall and rainfall erosivity at each time scale in the basin is studied,in order to evaluate the soil erosion of the basin,soil and water conservation measures work provides a reference.The main contents of this article are as follows:（1）The methods of rapid clustering and classical discriminant were used to study the erosive sub-rainfall and its characteristics between 30a in the basin,and the erosive rainfall was classified.Based on this,a comparative study on the classic algorithm of rainfall erosivity was carried out.The calculation method of R factor in the Universal Soil Loss Equation（USLE）was selected to calculate the secondary rainfall erosivity of each station in the basin,and then the true value of rainfall erosivity at each station was obtained by accumulating.（2）On the basis of the true value of rainfall erosivity in the basin,two simple algorithms for rainfall erosivity at the annual,monthly and daily scales were selected.The results were compared with the true values at different time and space scales and the statistical parameters were compared.It is found that the model F or YU model has good applicability in the basin,but there is still room for improvement.In addition,model E,which is widely used in China,is improved,and the cosine function which can reflect the seasonal variation of rainfall is found.The introduction of theαparameter part of the model has greatly improved the simulation effect and can be used to calculate the rainfall erosivity in the basin.（3）Through the Pearson correlation analysis of the univariate characteristics of the erosive rainfall and its combined characteristics and the secondary rainfall erosivity,it is found that the combined variable PI₆₀ has the highest correlation with rainfall erosivity,followed by rain intensity and precipitation,The correlation between rainfall duration and rainfall erosivity is not significant.On this basis,a simple calculation model of monthly rainfall erosivity using daily rainfall suitable for watershed is established by the nonlinear fitting method.（4）Using linear propensity estimates,moving averages,Mann-Kendall trend and mutation analysis,cumulative anomalies,Pettitt’s test,wavelet analysis,and Kriging space interpolation,with software such as Origin 2017,MATLAB 2018a,Surfer 9,and ArcGIS10.2 The precipitation and rainfall erosivity in the basin from 1989 to 2018 were analyzed by time and space distribution characteristics of different scales such as year and season,and it is clear that the key prevention and control areas of the river basin,that is,the northern part of the basin where the rainfall erosivity is large and the upward trend is particularly noticeable in the spring,the summer should pay attention to the possible soil erosion in the central region,and the winter should pay more attention to the relatively large southwest of the basin.