How reliable are our methods for estimating soil erosion by water?

Soil erosion is a problem of global significance for land management. Attempts to assess soil erosion by water encompass plot studies, monitoring, modelling, and the use of tracers. All of these approaches are shown to have shortcomings, calling into question the reliability of current estimates. There is an urgent need to develop approaches to estimating rates of soil erosion that are consistent with current understanding of erosion processes. Such approaches need always to be reviewed in the light of advances in understanding of processes. Only then can reliable estimates of soil erosion be made on which to base reliable land-use and policy decisions.