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item McGregor, Keith
item BINGNER R L - 6408-05-30
item FOSTER G R - 6408-05-30

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: The erosivity index (R) is used in the Revised Universal Soil Loss Equation to represent the effect of rainfall on erosion. Refinements in R values are needed to improve the accuracy of soil loss predictions. Although maps of R are based on measured values at several locations, most of the R values presently used in soil loss prediction were estimated from these measured values and other rainfall records. Erosivity values that are based upon recent analysis of rainfall data help to ensure that conservationists have the latest and best estimates possible for inclusion in soil loss prediction equations. In this study, rainfall data from 29 standard recording rain gages in the 21.3 square kilometer Goodwin Creek Watershed in northern Mississippi were used to compute erosivity values. These results indicate that the R value for this region should be increased by 30 percent over values presently recommended for use in RUSLE. Improvements in soil loss prediction benefit the Soil Conservation Service in recommending conservation practices to farmers, and thus also benefit farmers by being able to have confidence that soil losses from recommended practices can be expected to be below excessive soil erosion rates.

Technical Abstract: Rainfall erosivity (R) values during 1982-1992 were computed from 29 standard recording rain gages in or adjacent to the 21.3 square kilometer Goodwin Creek Watershed near Batesville, MS using Brown-Foster, McGregor-Mutchler, Agriculture Handbook 282, and Agriculture Handbook 537 recommended procedures. These annual R values were substantially higher than values currently recommended in Agriculture Handbooks 282 and 537 for northern Mississippi. Annual R values computed with the Brown-Foster equation for storms with at least 13 mm and from storms less than 13 mm if 15-minute rainfall intensities equaled 25 mm/h or more, and with a limitation on the maximum 30-minute intensity in the energy-intensity (EI) product of 64 mm/h still gave high R values. During 1982-1992, these values averaged 7515 (MJ-mm)/(ha-h), or 30 percent higher than the recommended R values. This study supports conclusions by McGregor et al. (1980) that R values for northern Mississippi should be increased. Excluding storms less than 13 mm reduced R values less than 4 percent. Similarly, limiting the maximum 30-minute intensity in the EI product also reduced R values by less than 4 percent. Inclusion of storms less than 13 mm/h when there were 15-minute periods with rainfall intensity equal or greater increased annual R values by less than 1 percent