Location: Southwest Watershed ResearchTitle: Rainfall erosivity: An historical review Author
Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2017
Publication Date: 6/8/2017
Citation: Nearing, M.A., Yin, S., Borrelli, B., Polyakov, V.O. 2017. Rainfall erosivity: An historical review. Catena. 157:357-362. Interpretive Summary: : Rainfall erosivity is an index that describes the power of rainfall to cause soil erosion. This study presents an historical review of the development of rainfall erosivity, primarily as done by USDA research scientists since the mid-1950s. Erosivity is used across the United States and around the world for assessing and predicting rates of soil erosion on agricultural lands. It is used extensively in the United States by the USDA-Natural Resources Conservation Service in daily planning for implementing on-farm conservation plans and policies. The quantification of erosivity is based on the energy and intensities of rainfall events. The formulas for computing erosivity have changed somewhat over the years based on new scientific results. There has been some confusion, primarily outside of the U.S., regarding the appropriate equations to use for calculating rainfall erosivity. This paper helps to clarify the historical progression of the concept, and guide the user in choosing the appropriate sets of equations to use for greatest accuracy. The result of the paper will be better implementation of USDA science both inside the U.S. and around the world.
Technical Abstract: Rainfall erosivity is the capability of rainfall to cause soil loss from hillslopes by water. Modern definitions of rainfall erosivity began with the development of the Universal Soil Loss Equation (USLE), where rainfall characteristics were statistically related to soil loss from thousands of plot-years of natural rainfall and runoff data. USLE erosivity combines the energy of the rainfall and the maximum continuous 30 minute intensity in the event. Energy of rainfall is estimated as a function of the storm intensity through the rainfall event. The USLE erosivity has been used effectively for conservation planning purposes for more than 5 decades. When the USLE was replaced by the Revised Universal Soil Loss Equation (RUSLE), a new energy-intensity equation was adopted. The new equation was not extensively tested prior to adoption, leads to significant under-predictions of erosivity, and was later replaced in RUSLE2. The RUSLE energy-intensity equation is no longer recommended by the RUSLE and RUSLE2 development teams. It should be understood that the calculations of erosivity as a whole are entirely based on rainfall intensities, and erosivity is an empirically-based index. The science indicates that the direct role of kinetic energy of rainfall as the driver of hillslope erosion in all cases is not warranted by the overall evidence, because many times interrill erosion is transport rather than detachment limiting, and kinetic energy of raindrops is not the driving force behind rill erosion. The USLE erosivity empirically explains much of the variance in the soil loss from natural rainfall erosion plots.