Mapping average annual runoff: a hierarchical approach applying a stochastic interpolation scheme

A novel approach for mapping river runoff is presented. It is based on a di saggregation of the mean annual streamflow measured at the outlet of a basi n to estimate water depths on elements of an exact partition of this basin. The developed technique is based on geostatistical interpolation procedure s to which a global constraint of water balance has been added. The methodo logy is illustrated by a case study from a tributary to the Rhone River, Fr ance. The results were compared to an established method-the nested approac h, and a cross-validation was performed for each mapping technique. The dis aggregation approach appears to give the most consistent results. Finally, two gridded maps were derived by applying the disaggregation twice to asses s water depth on an increasingly finer grid mesh. The global constraint of water balance was applied to each element of the coarser mesh to give estim ates for the finer one.