A two-parameter exponential rainfall depth-intensity distribution applied to runoff and erosion modelling

Most runoff and erosion models require rainfall intensity data of high temporal resolution, which restricts their application and predictive potential. In this paper, a simple exponential rainfall depth-intensity distribution (ERDID) was tested, involving only two storm characteristics that are easily calculated from rainfall intensity measurements: rainfall depth (P) and depth-averaged rainfall intensity (Ř). This distribution fitted well to tipping bucket rainfall intensity measurements during 30 storms of 33–81 mm in West Java, Indonesia. The ERDID was used to derive analytical expressions for the hydrological model variables of two commonly used erosion models, i.e. the ‘R’ factor in RUSLE and normalised soil loss in GUEST. The ERDID-based expressions reproduced hydrological variables for the 30 storms with high accuracy for both models (mean difference of ±4–17% for individual storms and between −2 and 14% on aggregate). A comparison of results obtained with the original (high temporal resolution) measurements and data resampled into 5-min intervals shows that resampling had a significant effect on calculations with the original models (cumulative values were decreased by 2–26%). In some cases the use of ERDID-based expressions with distribution parameters calculated from resampled data partially corrected this underestimation. The proposed rainfall depth-intensity distribution combines physically meaningful, clearly defined variables with theoretical simplicity and high descriptive accuracy and so provides a good scope for further application in runoff and erosion modelling.