The erosivity R-values given in USDA-Agriculture Handbook (AH) 703 for the eastern US and used in previous versions of RUSLE1 were based on rainfall data collected from approximately 1935 through 1957. During the development of RUSLE2, modern precipitation data from 1960 through 1999 were analyzed to develop new R-values. These R-values should be used in RUSLE1.06c instead of values from AH703. Also, the detail and quality of the new R-values for the western US are much superior to previous values, including those in AH703.
These new R-values are included in the climate (citylist) file that is downloaded from this Internet site with RUSLE1.06c. R-values for locations not represented in the RUSLE1.06c database can be obtained from the figure below for the eastern US. R-values for the western US, including the El distribution curves, should be obtained from the USDA-NRCS National RUSLE2 Database. This database is available at http://fargo.nserl.purdue.edu/rusle2_dataweb/RUSLE2_Index.htm. The existing El distribution curves in AH703 for the eastern US can be used in RUSLE 1.06c because these distributions are sufficiently close to those derived from the modern data. However, the El distribution curves in AH703 for the western US are significantly different from those developed from the recent analysis. The new distribution curves should be used for the western US instead of those in AH703. The new El distribution curves can also be obtained from the erosivity density curves shown below.
The figure below should be used rather than Figure 2.9 in AH703 to choose values for the 10-Yr El values used in RUSLE 1.06c for the eastern US. Continue to use figures from AH703 for choosing 10-Yr El values for the western US.
(note: There should only be one figure like this one and it should be in the section above)
The new 10-Yr El figure eliminates the wavy lines in Figure 2.9, AH703. The new smoothed curves in the figure below are consistent with the accuracy of RUSLE1.06c and 10 yr 24 hr precipitation lines. The new curves also represent how RUSLE1.06c captures main effects associated with how intense erosive storm vary with geographical location and how they affect P factor values.
Estimating R-Values and El Distributions Using RUSLE2 Erosivity Density Curves:
The erosivity density approach was developed to estimate R-values and their monthly distribution for RUSLE2. The erosivity density procedure improves accuracy and consistency, especially in the western US where precipitation data are limited. Erosivity density values are not greatly affected by mountainous terrain and can be estimated with less data than directly computing erosivity values, from detailed rainfall intensity data. Precipitation amount data, which is much readily available than intensity data, is used in conjunction with the erosivity density values to estimate erosivity. A value for monthly precipitation at a location is multiplied by the corresponding monthly erosivity density value given in the figures below to obtain an estimate of monthly erosivity.
(note: This figure should be in the section above related to 10 yr El)
The figures below are maps of erosivity density for the US. A monthly R-value can be obtained by multiplying a monthly erosivity density value by the precipitation amount for that month. The erosivity density value in the figures are in SI units. Monthly precipitation values must be in millimeters (mm) rather than inches to use these erosivity density values. To convert a precipitation value in inches to millimeters (mm), multiply by 25.4. To convert an R-value in SI units to US customary units, divide by 17.02. See AH703 for information on converting between SI and US customary units.
The erosivity density curves apply to all elevations for the summer months and up to an elevation of about 8,000 to 10,000 ft during the winter months. Monthly erosivity values will need to be reduced or even set to zero during the winter where the ground is continuously covered with snow or the soil is continuous frozen so that no erosion occurs.
(note the erosivity density figures below need to go here)
Cover-Management and Ridge Height Codes
RUSLE1.06 uses cover-management, ridge height, and row grade codes. These values much be selected according to RUSLE 1.06c definitions and guidelines so that RUSLE1.06s will give expected results. The document Recommended Option Codes for COVER MANAGEMENT CONDITION (should be in green with a link to the document) provides information to guide the selection of these codes.
New Version of RUSLE1.06c (June 1, 2003)
RUSLE1.06c is a new version that has been placed on the RUSLE1.06 Internet site. RUSLE1.06c contains significant changes so that it will give soil loss values comparable to those given by RUSLE2.