|Govers, G - K.U. LEUVEN, BELGIUM|
Submitted to: International Soil Conservation Organization Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: May 23, 1999
Publication Date: N/A
Technical Abstract: Although it is well known that soil rates vary considerably from year to year, this information is only rarely taken into account when interpreting soil erosion rates obtained from plot measurements: average soil erosion rates are usually cited and used without any mention of the uncertainty associated with them. We analyzed ca. 35 time series of soil loss and runoff obtained at different sites in the USA in order to quantify the uncertainty associated with the average soil erosion rates measured in a number of contrasting agronomical systems. Measured runoff values show coefficients of variation ranging from 5 to 60 percent of the mean value, with CI-10 values between 10 and 95 percent of the mean value. Variability for annual soil loss is even higher, with CI-10 values from 15 to120 percent of the average value. The variability found for runoff and soil loss variability than runoff variability. The variability found for runoff and soil loss is much greater than the variability in rainfall erosivity which has a relative confidence interval ranging from 25 to 40 percent of the mean. This reflects the fact that soil erosion is influenced by driving factors and resisting factors most of which are highly variable in time. Our analysis can be used to assess the uncertainty associated with an average soil loss estimation provided information about the length of the measuring period is available. For a 10-year measurement period, the 90 percent confidence interval is on average ca. 75 percent of the mean value, which implies that a reported 10 ton ha-1 yr-1 soil loss may in reality vary between 2.5 and 17.5 ton ha-1 yr-1.