Article describes rainfall erosivity, which is one of the main factors in surface soil erosion. In the first part, an overview of soil erosion process is given and its different forms presented. The main factors of the process are described and some methods for estimating soil erosion are cited. Further, a short overview of traditional and modern precipitation measurement methods is given. A special attention is given to the RUSLE method and its rainfall and runoff R factor. R factor was computed for Kamniška Bistrica, Solčava and Zgornje Jezersko measuring sites. On the base of R factors then were computed trends of erosivity. The results were then compared with each other. The trends were assesed by different methods: linear regression and Mann-Kendall statistic tests. I discovered similarity between different methods. The significance level depands on length of a series of values of erosivity R. The bigger length of the series gives the higher significance level. The Biggest deviation by month was found in springtime, when nature turns from spring to summer. Erosivity variates a lot among spatial distribution, relief and seasonality.