Radar polygon method: an areal rainfall estimation based on radar rainfall imageries

Abstract

This study presents a novel approach of areal rainfall estimation based on radar precipitation imageries that is capable of reflecting spatial variability in rainfall while maintaining methodological simplicity. We named this methodology "the radar polygon method" (RPM). In this approach, gages in the study area compete against each other to gain the grid cells of the radar precipitation field under its territory. The criterion of the competition between the gages is the similarity between the precipitation of the target grid cell and that of the gage location. We tested the applicability of RPM on four watersheds in Korean Peninsula in which 41 rain gage locations, used as the basis of polygon formation, exist. Even though RPM uses only the information regarding the spatial variability of rainfall extracted from the radar rainfall imageries without any geographical information, it obtains the polygon-like (or just polygon) shape of the governing territory for each of the gages in all four study watersheds. The difference between the radar polygon and the corresponding Thiessen polygon was especially notable for the areas where orography significantly affects the spatial variability of rainfall. Furthermore, the spatial variability of elevation within radar polygons was generally smaller than that within Thiessen polygons indicating that Radar polygon captures the topographic impact on rainfall that Thiessen polygon cannot. The major contribution of this study is that it suggested a novel field of using radar rainfall by providing an effective way of areal rainfall estimation which retains the simplicity of Thiessen polygon approach and is not affected by the relatively low accuracy of radar rainfall imagery.