[AHW33-11] Applying a data-based rainfall-runoff modeling approach to interpret the mechanisms of decreasing spatial variability of subcatchment-specific discharge with increasing subcatchment area
キーワード：降雨流出機構、空間スケール、固有性
The weak law of large numbers can mathematically explain why there is a decrease in the spatial variability of river flows from subcatchments when travelling downstream, while catchment area increases. On the contrary, there is no process-based interpretation of this phenomena in today’s catchment hydrology literature. The present study attempted to interpret the mechanisms of decreasing spatial variability of river flow with increasing catchment area in terms of a data-based rainfall-runoff modeling approach. First, we collected hydrological data from HJ Andrews Experimental Forest, Oregon, U.S.A. to plot the subcatchment specific discharge against subcatchment area. Second, we applied a data-based rainfall-runoff modeling approach to identify the unique rainfall-runoff processes for all the subcatchments in order to understand why the spatial variability of subcatchment-specific discharge decreases with increasing subcatchment area. The results showed that (1) the spatial variability of subcatchment-specific discharge is mostly explained by the spatial variability of faster processes in the subcatchments and (2) the decrease of spatial variability of faster processes in the subcatchments caused decreasing spatial variability of subcatchment-specific discharge with increasing subcatchment area. These results suggest that, among subcatchments, spatial variability of slower processes occur deep in the ground.