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Rainfall and soil erosion is a result of the interaction of rainfall, rainfall is the driving force of erosion, soil is eroded object. In land area in purple, rainfall is the main driving force of soil erosion. Erosivity of rainfall is reflected in this role, it refers to the potential of soil erosion caused by rainfall capacity is a function of rainfall characteristics. Purple soil hilly area due fragile ecological environment, reclamation rate, sloping land and more features, more serious soil erosion. On purple soil erosive rainfall and erosion characteristics of research is to understand and master the law on the basis of soil erosion, but also for the Purple Soil Region Soil and Water Conservation provides a theoretical basis and technical support. In this paper, the study area rainfall data and 5 °, 10 °, 15 °, 20 ° and 25 ° five different slope erosion runoff observation cell observation data, systematic study of the characteristics of the rainfall in hilly areas, rainfall erosivity, slope characteristics of soil erosion and land erosion impact factor. The results showed that: (1) Soil and Water Conservation Experimental Station in Sichuan Suining average annual rainfall of 908.78mm, the average number of rainy days was 111.29 days, the annual number of days with 30% presence of rain. According to Pearson Ⅲ type curve analysis, 1% year annual rainfall is 1389.70mm, annual maximum daily rainfall of 281.20mm; 5% annual rainfall is 1231.63mm, annual maximum daily rainfall of 204.45mm; 50% of annual rainfall is 897.17mm, annual maximum daily rainfall of 88.73mm; 95% annual rainfall of 625.52mm, annual maximum daily rainfall of 49.37mm. Year in June, July and August are the most concentrated rainfall in the month, accounting for 18.23% annual rainfall, 17.79%, 17.34%, a total of 53.37%, in December and January the following year, in February rainfall is about 45.1mm, accounted for only 4.96 percent. Various types of rainfall in moderate to 263mm, light rain is 258.74mm, accounted for 60% of annual rainfall, heavy rain, heavy rain, heavy rain rainfall of 162.03mm, accounting for 18% of annual rainfall. Various types of rainfall frequency, the number of rain total annual rainfall for 79%, followed by moderate rain 15%. Rain events have occurred in each month, moderate record did not occur only in January, heavy rain occurs mainly in April-November, heavy rain occurred in April-September, heavy rain and heavy rainfall occurred in June, August. (2) the study area average annual rainfall erosivity values ??4436.29MJ · mm/hm2 · h), rainfall erosivity standard deviation of 2206.51, the coefficient of variation Cv of 0.50. According to Pearson Ⅲ type curve analysis, 1% of annual rainfall erosivity 12276.08 MJ · mm / (hm2 · h), 5% annual rainfall erosivity is 8822.83 MJ · mm / (hm2 · h), 75% annual rainfall erosivity to 2853.40 MJ · mm / (hm2 · h). Annual distribution of rainfall erosivity values ??showed a single peak, August rainfall erosivity value reaches the maximum 1213.18MJ · mm (hm2 · h), 6,7,8 month rainfall erosivity values ??of the year accounted for 73.63% . R-value of annual rainfall and the related analysis, the correlation coefficient r = 0.928, significance level was very significant. Through the monthly rainfall erosivity rainfall pattern with various correlation analysis found that monthly rainfall erosivity associated with the highest degree of heavy rainstorm, the correlation coefficient r = 0.985, followed by heavy rain and moderate rainfall ~ correlation coefficient is 0.976. (3) through different gradients generated during the year 2001 to 2004 the number of times of rainfall erosion frequency analysis found that the slope for a certain period of time and erosion caused by rainfall events or otherwise has a very significant impact. According erosional features developed in Purple Soil Hilly 5 °, 10 °, 15 °, 20 °, 25 ° slope farmland soil erosion rainfall thresholds were 48mm, 37.6mm, 33.2mm, 32.4mm, 24.2mm; average rain Strong critical values ??were 5.26mm / h, 5.20 mm / h, 4.86 mm / h, 4.51mm / h, 4.63mm / h. (4) to analyze the characteristics of soil erosion, soil erosion was found with the relationship between the annual rainfall is not obvious. Different types of each month and the month of rainfall rainfall erosion analysis, 5 ° cell observations show erosion and moderate rain, heavy rain, heavy rain gradually increased correlation between the correlation coefficient r = 0.787,0.842,0.912; 10 ° plot observations show erosion and moderate rain, heavy rain, heavy rain correlation between the first increase and then decrease, the correlation coefficient r = 0.706,0.776,0.773:15 ° plot observations show erosion and moderate rain, heavy rain , the correlation between Esen storm weakened further enhance the correlation coefficient r = 0.775,0.821,0.801; 20 ° plot observations show erosion and moderate rain, heavy rain, heavy rain gradually increased correlation between the correlation coefficient r = as 0.779,0.791,0.853; 25 ° plot observations show erosion and moderate rain, heavy rain, heavy rain weakened the correlation between first and then increased, the correlation coefficient r = 0.757,0.754,0.825. Overall, heavy rain, heavy rain and erosion of the relationship between most closely. (5) through correlation analysis, found that the amount of annual erosion slope and correlation coefficient r = 0.749, according to erosion and slope of each month correlation analysis found that in April, May, June, September correlation coefficient (r) have reached more than 0.93, July low correlation coefficient of only 0.738 0.242,8 month. Do each month erosion and R-value scatter found that only the month R value reached 900MJ · mm / (hm2 · h) The above is only a greater erosion. Through correlation analysis showed that the slope of the cell and monthly rainfall erosion erosion volume showed a higher degree of correlation, the correlation coefficient r values ??above 0.8, especially in the 5 °, 10 °, 15 ° plot correlation coefficient r = up to 0.9. Soil erosion and rainfall erosivity, slope and other factors are more closely related to the function through a regression analysis of soil erosion month empirical formula.
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