Submitted to: Climate and Weather Research Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 17, 1995
Publication Date: N/A
Interpretive Summary: One feature of the Water Erosion Prediction Project (WEPP) program is that predicted erosion at a given location is sensitive to the weather conditions at that location. Although this feature can be advantageous in certain situations, it causes problems when trying to determine erosion trends over a large area. This problem occurs because weather data are available only at a limited number of sites. A program was developed that, when used with WEPP and the weather generator CLIGEN, gives accurate predictions of erosion trends over large geographic areas. Results were consistent with those obtained using other prediction tools. This procedure allows the user to take advantage of the flexibility of WEPP over other prediction tools to determine regional trends that are independent of local weather characteristics.
Technical Abstract: The purposes of this study were: 1) to investigate the simulation period necessary to obtain stable long-term annual averages of soil erosion for various environmental conditions, 2) to investigate the effects of station-to-station variability of CLIGEN input data on the average annual soil loss predictions obtained from WEPP, and 3) to develop a methodology for reducing unreasonable and undesirable levels of such variation while maintaining the integrity of the models in representing regional trends in erosion differences due to climate. The results showed high variations of the average annual soil loss results when the only changes in the input were the climate parameter values used by CLIGEN from one weather station to another. A model was proposed to average climate parameters of the station under consideration with the parameters of the surrounding stations. A comparison of equal soil loss contours obtained after averaging parameters and isoerodent lines from the RUSLE model showed that both reveal similar trends. Also, the comparison of the average annual soil loss predictions from station to station required the definition of a minimum simulation period in order to remove climatic variability and to obtain stable long-term averages at each station. The calculation of weather characteristics as well as many of the CLIGEN testing studies are often based on 30 years because 30-year averages of daily values of the main weather variables (precipitation and temperatures) are considered to be statistically representative of the general populations. Our study showed that 30 years are not enough to obtain stable WEPP predictions of the average annual soil loss.