Submitted to: Journal of Environmental Modeling and Software
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2003
Publication Date: 2/1/2004
Citation: Van Pelt, R.S., Zobeck, T.M. 2004. Validation of the wind erosion equation (weq) for discrete periods. Journal of Environmental Modeling and Software. 19(2): 199-203. Interpretive Summary: Farm policy includes provisions for agricultural producer compliance with soil conservation and environmental standards prior to individual approval for such farm support programs as subsidies and loan deficiency payments. For several decades, the United States Department of Agriculture (USDA), Natural Resources Conservations Servie (NRCS) has used various versions of the Wind Erosion Equation (WEQ) to assess producer compliance with limitations of wind-induced soil loss. WEQ uses inputs of soil texture, climate, wind erosivity, and tillage effects on surface roughness and crop residue to predict soil loss. WEQ was developed in Kansas in 1965 and little is known about its accuracy elsewhere. We compared the wind erosion predictions of WEQ with field measured data from seven locations across the United States, two of which had multiple years of data. With the exception of the two sites in western Kansas and eastern Colorado (close to the region where WEQ was developed), WEQ only predicted, on average, about half of the measured wind erosion. Wind erosion data for Big Spring, Texas, collected during two years with near average winds were used to investigate whether or not local calibration could improve the performance of the model. By adjusting either the climate or the soil factors, WEQ could be made to accurately predict the measured erosion for those two years. While adjustments to the climate factor resulted in excellent agreement, adjustments to the soil factor could be explained by the texture of the sandy material left on the soil surface after an intense rainfall event.
Technical Abstract: The Wind Erosion Equation (WEQ) is currently used by the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) to insure compliance with government guidelines for soil loss from agricultural land. The model uses inputs of soil texture, annual mean climate data, statistically derived wind energy apportionment tables, and field management options to predict soil loss on a management period and annual basis. In this study we compared estimates of wind erosion derived from the sums of field measurements at seven locations, two of which had multiple years of observations (a total of 14 periods of comparison), with the predictions of WEQ. WEQ under-predicted the observed estimates 11 of the 14 periods by as much as a factor of nine. For the three periods that WEQ over-predicted observed erosion estimates, the factor was less than 1.5. Across all sites and periods, WEQ only predicted about 53% of the observed estimated erosion. Analysis of two average years at Big Spring, Texas, indicated that WEQ could be locally calibrated by use of increased climatic (C') and soil erodibility (I) values as well as combinations of the two.