Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2002
Publication Date: N/A
Citation: Interpretive Summary: The power of rainfall to cause soil erosion is called "erosivity" of rainfall. Rainfall erosivity is usually calculated from the amount of rain that falls during a storm, as well as the intensity (amount of rain per unit time) at which it falls. This information is generally taken from charts on rain gauges that are used to collect rainfall information. Although it might seem like a trivial task, taking such information is an extremely time consuming and expensive process. This study was undertaken to help reduce the time and expense of determining rainfall erosivity from rainfall data by reducing the number of charts necessary to read for computing erosivity. Small storms do not cause erosion. By determining which small storms could be ignored in the process of calculation, the work for reading rain charts for these storms can be eliminated. Briefly, the results of this study showed that rains less than 12 mm in total depth can be ignored in the calculation of rainfall erosivity with essentially no loss of accuracy in the estimation of erosivity. The impact of this research has been to reduce the cost and time necessary to calculate the values of rainfall erosivity that are necessary to predict soil erosion.
Technical Abstract: Determination of a practical threshold for separating erosive and non-erosive rainfall events can reduce the amount of work necessary to read rainfall charts and to calculate rainfall erosivity. The objective of this study was to develop a method of determining practical thresholds for erosive rainfall events and to evaluate its effectiveness for calculation of erosivity. Rainfall and runoff data measured for three plots and a small watershed from 1961 to 1969 at the Zizhou experimental station of the Yellow River Basin in China were used. Three thresholds for separating erosive events were given by using different types of rainfall data: a) 12mm for storm rainfall amount, b) 2.4 mm h-1 for average rainfall intensity, and c) 13.3 mm h-1 for the maximum 30 min. rainfall intensity. All methods had less than 0.1% overall error in the prediction of the erosivity value. Peak intensity provided the greatest accuracy for separating erosive rains, followed by rainfall intensity and then rainfall amount. A total of 79%, 77%, and 88% of the total number of events were omitted from the calculations using rainfall amount, average rainfall intensity, and 30 min. peak intensity, respectively. Any of the above three thresholds may be used according to data availability and desired accuracy of the erosivity estimation.