A Global Survey of Sediment Yield

Sediment yield data were collected from national institutes and other sources. Attention was paid to data reliability in general. The global pattern of variation in net erosion is shown in a separate map. Sediment yield is affected by many factors such as climate, relief, soil, vegetation, and human influence. Tectonic instability and volcanic activity are also of importance. Climate is one of the major factors controlling net erosion rates and is chosen as a basis for division in statistical analysis. Sediment yields are very high in the 'Af' climatic group, i.e. tropical humid climate without a dry period. Contrary to what was expected, tropical climates with a dry season do not show values as high as in the 'Af' group. Warm temperate climates with a dry season, 'Cs' and 'Cwa' climates, exhibit high sediment yields. Among the warm temperate climates without a dry period, Cfa climates have few rivers with low sediment yield whereas Cfb climates have many rivers with low yield. Boreal climates (cold temperate climates) contain rivers, most of which have low values except for some Chinese data in Dwa and Dwb climates. In boreal climates within another climatic zone, but being boreal as a consequence of altitude, 'Ds' and 'Df', sediment yields are usually higher than in the zonal boreal climates. Runoff has been used as a variable representing climatic conditions. Relationships between runoff and sediment yield are shown in diagrams for different climatic groups. As there are different relationships or the lack of a relationship between runoff and sediment yield in the different climatic groups, there is no universal statistically significant global correlation between runoff and sediment yield which is valid for all climates.