Temporal and Spatial Discontinuity of Radar/Raingauge-Analyzed Precipitation That Appeared in Relation to the Modification of Its Spatial Resolution

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To quantitatively evaluate how different methods for creating 5 km mesh Radar/Raingauge-Analyzed Precipitation (R/A) affected annual precipitation, we compared three kinds of 5 km mesh R/A during 1991–2009 by devoting attention to the modification of its spatial resolution. It was, respectively, 5 km until March 2001, 2.5 km from April 2001 to December 2005, and 1 km from January 2006. For creating 5 km mesh R/A, three methods were adopted, i.e., (I) spatial average of 2.5 km or 1 km mesh was calculated. (II) Maximum value of 2.5 km or 1 km mesh was selected. (III) For creating 2.5 km mesh from 1 km mesh, spatial average of 3 × 3 1 km mesh was calculated considering the representative area of each mesh. For creating 5 km mesh from 2.5 km mesh, maximum value of four 2.5 km mesh was selected. The method III is suggested by JMA. We found abrupt changes of annual precipitation were seen in 2000/2001 (method I) and 2005/2006 (method II), both of which were artificial temporally and spatially compared with AMeDAS data. The 5 km mesh R/A created by the method III was statistically homogeneous, so we recommend that we should adopt the method III.