Impact of Cligen Parameters on Wepp-predicted Average Annual Soil Loss

Abstract

The combination of the weather generator program CLIGEN and the Water Erosion Prediction Project (WEPP) model provides a way to predict runoff and erosion for individual rainfall events for long periods of simulation. The purposes of this study were to: 1) investigate the required simulation period necessary to obtain stable long-term annual averages of soil erosion for various environmental conditions; 2) investigate the effects of station-to-station variability of CLIGEN input data on the average annual soil loss predictions obtained from WEPP; and 3) develop methods 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, even when the climate was fairly uniform from station to station. A model was proposed to average climate parameters of the station under consideration with the parameters of the surrounding stations. Results obtained using these averaged input values were much more consistent from one station to another for periods longer than 50 years. For shorter periods (30 years), the annual variability of soil loss was larger than the variability induced by climate parameters and averaging these parameters does not improve the results. A comparison of equal soil loss contours obtained after averaging parameters and isoerodent lines from the RUSLE model showed that both reveal similar trends. In mountainous regions this model was not applied because changes in climate of two adjacent stations were sometimes abrupt.