Global assessment of land vulnerability to water erosion on a 1/2 degrees by 1/2 degrees grid

A simple methodology is presented for assessing the risk of water erosion at the global level. It uses a 1/2 degrees latitude by 1/2 degrees longitude soil database, developed at ISRIC, and auxiliary databases on climate and land cover with a similar spatial resolution. Area estimates are presented for (1) susceptible areas, as determined by rainfall erosivity, topography and soil erodibility, and (2) vulnerable areas as further determined by the pressure of current land use. Model output for vulnerability is evaluated against observed data on severity of soil degradation by water as presented on the map of human-induced soil degradation (GLASOD). Cross-tabulation of the vulnerability and GLASOD subsets gave a significant Cramer's correlation coefficient of 0.72 (P much less than 0.005). Thus a fair geographic agreement was observed between the grid cells considered vulnerable to water erosion, under current conditions of land cover, and regions in which water erosion occurs currently. The qualitative model can serve to raise awareness on issues of soil degradation by water at the global level by identifying regions at risk, where more detailed studies are needed. However, it does not provide any information on the actual rate of erosion at the field scale, nor on the associated decrease in crop productivity and biodiversity. The study of productivity changes associated with water erosion, at different scales, is currently an important topic on ISRIC's research agenda.