Tham khảo tài liệu 'international perspectives on global environmental change part 10', khoa học tự nhiên, công nghệ sinh học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Late Quaternary Environmental Changes and Human Interference in Africa 259 methods remains a challenge. Beckedahl 2002 mentions a prediction error of 55 by applying the USLE on African soils. Apart from the complex interaction of factors which has to be determined on test sites the inclusion of erosive rainfall events in soil erosion formulations remains a problem. Indices of rainfall such as mean rainfall wettest month or other indices which are derived from rainfall data are rarely capable of predicting soilerosion events and may be misleading de Ploey et al. 1991 . Methods based on the determination of magnitude-frequency relationships of individual rainfall events that are beyond the threshold of erosive rains may provide an alternative de Ploey et al. 1991 . Such methods enable the determination of the likelihood of erosive rains and provide information on the cumulative effects of individual rainfall events. This information makes it possible to deduce the Cumulative Erosion Potential CEP de Ploey et al. 1991 . The CEP-Index is based on the magnitude-frequency concept of Wolman and Miller 1960 . According to this concept the impact of extreme events is compensated by its lower frequency whilst the cumulative effect of more frequent events of a certain magnitude results in higher output. Figure 1 shows the magnitude-frequency relationship and the CEP-Index table 1 for some stations in Lesotho Kenya and Zimbabwe. The magnitude-frequency relationship and the CEP have been calculated from data provided by de Ploey et al. 1991 Calles and Kulander 1996 and Romer 2004 . At stations where recurrence intervals of erosive rains are very short the CEP-Index indicates a high potential of soil erosion. However even if the concept of the cumulative effects of discrete rainfall events provides a reasonable approach to erosion events the problems involved in a numerical calculation of the complex repercussions between seasonal effects vegetation growth periods rainfall .
