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 to the USLE methodology were assessed by two methods
of erosive rains determination. The first method (VAR1) defined erosive rains by intensity
≥ 0.4 mm· min⁻¹; total ≥ 12.5 mm and the second method (VAR2) by intensity
≥ 6 mm· 15 min⁻¹; total ≥ 12.5 mm. Database contained one minute precipitation data
from four automatic stations in the Czech Republic for the period of 2000–2005. Two-way
analysis of variance (ANOVA) showed a statistically highly significant difference between
the annual number of erosive rains determined by the two methods. The rains simultaneously
complying with two following criteria (30 min intensity lower than 15 mm·h⁻¹ and
sum of 40 mm) were not generally classified as erosive rains according to VAR2. The number
of erosive rains determined by VAR2 most often reached 40 to 50% of VAR1 results.
Two-way ANOVA proved highly significant differences between the 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 are generally not considered as erosive rains. The
results of kinetic energy of the erosive rains determined by VAR2 most often reached 60
to 70% of VAR1 results. Two-way ANOVA has not proved a statistical difference between
annual values of R factor of erosive rains determined by the two methods. According to
VAR2 the rains with R factor lower than 5 are in general not included into annual Rfactor value.The results of annual R factor values of erosive rains determined by VAR2are about 25% lower than the results of VAR1.