Daily Adjustment for Wind-Induced Precipitation Undercatch of Daily Gridded Precipitation in Japan

Abstract

The northern Japan facing the Japan Sea is known for its heavy snowfall. As snowfall is of great importance as a water resource, accurate measurements are required. We develop an optimal method for adjustment of wind-induced precipitation undercatch for rain-gauge-based daily gridded precipitation data in Japan. In Japan Meteorological Agency's surface observation network, wind speed data are not measured at all precipitation stations; therefore, we tested three approaches for applying wind correction using four years' observational data (2009–2012). First, we interpolate corrected precipitation by using only stations, which measure wind; second, we define gridded correction parameters, interpolate uncorrected precipitation of all stations, and adjust gridded precipitation; third, we interpolate corrected precipitation by using wind data of Japan Meteorological Agency's surface network and a reanalysis at the stations where wind are not measured. Water budget analysis over the mountainous regions (dam's catchments) indicated that the best result among the three was obtained by compensating wind speed using high-resolution meteorological reanalysis data, followed by a method that applies daily correction parameters to daily gridded precipitation data. The best method increased the winter (December–February) precipitation amount by 12.7% in northern Japan, and the bias in the annual hydrological balance was reduced from 33% to 26% over the mountainous terrain. Proper consideration of the rain gauge meta information, such as the existence/absence of a wind shield, is critically important for quantitative assessment of solid precipitation, especially in regions of heavy snowfall such as northern Japan.