Influence of Anomalous Warmer Winter on Statistics of Measured Winter Precipitation Data

Abstract

The winter of 2006/07 in Japan was the warmest in more than 100 years. To evaluate the effects of such an anomalous warmer winter on measured winter precipitation data, gauge-measured precipitation amounts from an area near the Japan Sea coast were compared with values corrected to account for undercatch errors due to the effect of wind. The measured data in this area of Japan are usually 60%?90% of the corrected winter precipitation because of large systematic errors in solid precipitation measurements. However, the measured precipitation for the winter of 2006/07 was much closer to the corrected precipitation because more precipitation than usual fell as rain rather than as snow. Series of precipitation data for 30 winters were corrected by accounting for undercatch errors, and the corrected data were compared with measured data. Both datasets showed the similar tendency that the warmer the winter is, the smaller the winter precipitation is. However, the ratio of the negative relationship between winter precipitation and mean winter temperature, which was calculated using corrected winter precipitation, is 2 times that calculated using measured winter precipitation data. These results suggest the possibility that measured winter precipitation data may show fictitious changes because of changes in the form of precipitation, even though the actual amount may not have changed. Moreover, statistical studies that fail to consider systematic errors in precipitation measurements may possibly result in misinterpretations of the tendency and fluctuation of winter precipitation.