Erosion is a problem endemic to semi-arid lands. In more humid climates, vegetation holds soil in place, limiting the amount of material that can be carried down hill slopes and into rivers and streams. In extreme arid climates there is insufficient flow to transport sediment. It is in semi-arid lands - where there is incomplete vegetation cover yet sufficient water to move surface materials, especially during and after intense rain storms - that maximum sediment is carried downstream.

Working solely from the general relationship between precipitation and sediment production, the simplest of potential erosion maps can be made. This map of erosion potential is based on annual precipitation data from Oregon State University http://www.ocs.orst.edu/data/PRISM/data/PRISM_new.html, which has been combined with a general relationship between annual precipitation and basin sediment production. It ignores many important factors that control sediment production and transport, such as soil characteristics, actual vegetation cover, slope, and rates of rainfall (a few large precipitation events move more sediment than many small events having the same annual total).

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