Effects of Spatial Scales on Runoff / Sediment Transport in Mountain Catchments (3) -Review for the Treatments of Numerical Models

Abstract

　We reviewed the treatment of spatial scales in numerical models of runoff and sediment transport to elucidate current problems and to identify avenues for future research. We specifically examined the following questions: (1) Which spatial scale is used in existing modeling and how was it decided? (2) What spatial information was used? (3) Do the governing equations differ with spatial scale? Results show that the smallest spatial scale in distributed models was determined by the spatial resolution of spatially distributed information used in modeling, although lumped models were applicable at any scale. Some physical parameters used in modeling, aside from elevation, land use and vegetation cover, were not based on field-based information. Results demonstrate that the governing equations differ depending on locations within the watershed (i.e., hillslopes and channels) presenting different processes for runoff and sediment transport. Nevertheless, no report of the relevant literature describes a study with changed governing equations along with the changes in spatial scales. We also reviewed modeling studies of how we should treat the effects of spatial scale in runoff modeling, which revealed that they had reported minimum and the maximum spatial scales for lumping runoff mechanisms and the relative importance of spatial data used as input and parameters, although no attempts have been reported for a change in governing equations with spatial scale. We were unable to find similar studies of sediment runoff modeling. In summary, we suggest improvement of these findings and their use for modeling rainfall runoff and sediment transport mechanisms for better hydrological science.