A Comparison of the R-factor in the USLE and RUSLE
The R-factor in the Universal Soil Loss Equation /Revised Universal Soil Loss Equation (USLE/RUSLE) characterizes the climatic influence on the average rate of soil loss. The way in which the R-factor was calculated for RUSLE differs from that for the USLE. Rainfall intensity data at 6-min intervals from 41 long-term sites in the tropical region of Australia were analyzed to determine the discrepancy in the calculated R-factor as a result of using different unit energy equations and different rainfall thresholds. The mean annual rainfall varies from 261 to 4030 mm for the 41 sites. The calculated R-factor using the unit energy equation for the USLE is greater than that using the unit energy equation recommended for RUSLE. The typical difference is about 10% for the tropical region of Australia. The difference tends to increase as peak rainfall intensity decreases. The percentage difference in the R-factor due to different unit energy equations was found to be significantly correlated with the ratio of the R-factor to mean annual rainfall. The discrepancy in the calculated R-factor due to different rainfall thresholds increases as mean annual rainfall decreases because the relative contribution to the R-factor from small storm events increases in low rainfall areas. Lowering the rainfall threshold from 12.7 mm to 0.0 mm would on average increase the calculated R-factor by 5% for the same region. Relationships based on mean annual rainfall and the R-factor were developed so that the magnitude of the discrepancy in the calculated R-factor due to different unit energy equations and different rainfall thresholds can be readily assessed.
Transactions of the ASAE
© 1999 American Society of Agricultural and Biological Engineers (ASABE). The attached file is reproduced here in accordance with the copyright policy of the publisher. Please refer to the journal's website for access to the definitive, published version.