Comparison of two methods of erosive rains determination

Abstract

Number of erosive rains, kinetic energy of erosive rains and factor of erosive efficiency of rains according the USLE methodology were assessed by two methods of erosive rains determination. The first method (VAR1) defined erosive rains by intensity higher than 0.4 mm.min-1; total higher than 12.5 mm and the second method (VAR2) by intensity higher than 6 mm.15min-1; total higher than 12.5 mm. Database contained one minute precipitation data from four automatic stationa in the Czech Republic for the period of 2000 – 2005. Two-way analysis of variance (ANOVA) showed a statistically highly significant difference in annual number of erosive rains by the use of both methods. The rains simultaneously complying with two following criterions (30 min intensity lower than 1.5 cm.hod-1 and sum of 40 mm) were not generally classified as erosive rains according to VAR2. Number of erosive rains determined by VAR2 most often reached 40 to 50% of VAR1 results. Two-way ANOVA proved highly significant differences between a kinetic energy values for the erosive rains determined by VAR1 a VAR2. According to VAR2 the rains with kinetic energy lower than 3 MJ.ha-1 are not considered as erosive rains generally. The results of kinetic energy of the erosive rains determined by VAR2 most often reached 60 to 70% of VAR1 results. Two-way ANOVA was not proved a statistical difference between annual values of R factor of erosive rains determined by both methods. According to VAR2 the rains with R factor lower than 5 are not included into annual R factor value in general. The results annual R factor values of erosive rains determined by VAR2 are about 25% lower then the results of VAR1. Correlation between number of erosive rains, kinetic energy of erosive rains and annual R factor value assessed by both methods showed a statistically significant relationship. Thus the convention formulas between results of both methods (VAR1 and VAR2) were derived by linear regression. As conclusion we ca