Revised Universal Soil Loss Equation 2 - RUSLE2 Development

RUSLE2 Development

RUSLE2 Developers

Development of RUSLE2 began in November 1993 and was accelerated when the USDA-NRCS announced in August 1998 that it would implement RUSLE2 in its field offices starting in 2002. Development of RUSLE2 was a joint project involving the USDA-Agricultural Research Service(ARS), the USDA-Natural Resources Conservation Service (NRCS), and University of Tennessee. The USDA-ARS provided overall leadership to the project, especially in developing the scientific components of RUSLE2. The University of Tennessee provided leadership in developing the computer aspects of RUSLE2 including its computational engine, user interface, and computer code.

RUSLE2 was developed to be land-use independent and to serve a diverse set of users. The principal application of RUSLE2 is conservation planning in the local, county-level field offices of the USDA-NRCS. The NRCS advised the project on its requirements for RUSLE2, evaluated RUSLE2, and developed a comprehensive RUSLE2 operational database.

Objectives in Developing RUSLE2

The objectives in developing RUSLE2 were to: scientifically enhance the USLE/RUSLE1 approach for estimating soil loss, have a modern graphical user interface, easily accommodate conversion between customary US and SI (metric) units, use as much of the RUSLE1 database as possible, and have a powerful and easy-to-use program so that USLE/RUSLE1 users could conveniently switch to RUSLE2. The fundamental empirical equation structure of the USLE/RUSLE1 was retained in RUSLE2 to differentiate RUSLE2 from process-based simulation models that mathematically simulate the many processes that affect soil erosion.

Type of Model

RUSLE2 does not replicate field processes. Instead, the RUSLE2 user describes the specific field condition, and RUSLE2 uses that description to compute erosion. RUSLE2 uses both empirical and process-based equations. In fact, some of RUSLE2's process-based equations are more sophisticated than those in any other model. RUSLE2 is a hybrid model that uses the USLE equation structure to provide great robustness along with process-based equations to extend RUSLE2 significantly beyond the limitations of the purely empirically based USLE. Robustness means that you can apply RUSLE2 with the confidence that RUSLE2 will give realistic answers even if the inputs are not right on the money. The following steps were followed to develop RUSLE2.

Step 1: Move RUSLE1.06 into RUSLE2

The first step in the development of RUSLE2 was to move RUSLE1.06 into the RUSLE2 interface and its computational engine. RUSLE2 makes its computations on a daily time step rather than the RUSLE1 half-month time step and the USLE crop stage time step. Also, RUSLE2 uses a full mathematical integration procedure rather than the approximate procedure used in the USLE and RUSLE1. These changes alone represent a major improvement in RUSLE2 over the USLE and RUSLE1.

Step 2: Review Equations

The next step was to thoroughly review every equation and coefficient value used in RUSLE1. In some cases, the same equations were kept in RUSLE2 but recalibrated with new scientific data added to the database. In other cases, new equations replaced old equations. In yet other cases, a totally new set of equations was used to give increased capability to RUSLE2. As a result, RUSLE2 is on the cutting edge of erosion-prediction technology.

Step 3: Calibrate

The next step was to calibrate RUSLE2 with the new equations for a wide range of conditions so that all of the program code, equations, and logic in RUSLE2 were exercised and checked. RUSLE2 was run by its developers for every possible condition that they could imagine. After the developers finished with their evaluations, NRCS evaluated RUSLE2 as it would be applied in their field offices.

Step 4: Develop Databases

The developers assembled a core database for the conditions used to calibrate RUSLE2. This database served as the reference and guide to the USDA-NRCS development of an extensive operational database. The input values used in RUSLE2 must be consistent with the values intended by the RUSLE2 developers. This consistency is achieved by making sure that values in the operational database are comparable to those in the core database. RUSLE2 users should use information from the NRCS national RUSLE2 database as much as possible. The NRCS national RUSLE2 database is available on the Internet at http://fargo.nserl.purdue.edu/rusle2_dataweb/RUSLE2_Index.htm. Contact the NRCS state agronomist in your state for additional information on the NRCS data used in RUSLE2.

Step 5: Develop RUSLE2 Climate Inputs Based on Modern Data

Although not strictly a RUSLE2 development, the Illinois State Water Survey, NRCS, University of Tennessee, and ARS analyzed modern weather data to develop new values for erosivity, precipitation, and temperature for use with RUSLE2. That information is contained in the ARS RUSLE2 database and the NRCS RUSLE2 national database.

Step 6: Continue Development and Maintenance

Development and maintenance of RUSLE2 is an ongoing project supported by the ARS, NRCS, and University of Tennessee. We have made a concerted effort to ensure that RUSLE2 works well and is error free. Please report errors so that we can fix them. See the section on "Getting Assistance" for instructions on reporting errors.

Step 7: Document

RUSLE2 has been extensively documented by informal technical reports. A detailed draft but incomplete Reference User Guide is available that describes how most of RUSLE2 works. This Reference User Guide is expected to be complete by mid 2003. The scientific documentation of RUSLE2 will be finished by late 2004. A draft copy of the Reference User Guide is available for download from this Internet Site.

Additional information on the development and application of RUSLE2 is available from the University of Tennessee, by contacting he NRCS State Agronomist in your state, and at the NRCS Internet site mentioned above. http://fargo.nserl.purdue.edu/rusle2_dataweb/RUSLE2_Index.htm