The flowering of the Japanese apricot (Prunus mume Sieb. et Zucc.), which is representative of phenological events in winter, is widely observed in Japan. Shifts in the flowering date are related to climate change such as global warming and the urban heat island effect. In the present study, we analyzed trends in the flowering date of the Japanese apricot to clarify temporal and spatial variation from 1961 to 2007 using statistical methods. Phenological and meteorological data were recorded by the Japan Meteorological Agency at 34 meteorological stations in Japan. By linear regression analysis of the flowering date (expressed as the day of the year, DOY) against the year, mean trends of this parameter were shown to be significantly negative (i.e. advancing flowering) at 15 stations (44% of the total), with no significant positive trends. Comparison of the mean flowering dates in the 2000s with those in the four subintervals (the 1960s-1990s) indicated that the number of stations showing significant negative trends decreased from the 1960s to the 1990s. In a few phenological stations, the flowering date was delayed. The first principal component of the trends accounted for 55% of the variation in the flowering date for the period 1961 to 2007 at 34 stations and reflected chronological progression in the flowering. In particular, a recent trend since the mid-1990s contributed to advancing trends during the period 1961-2007. From the mid-1980s, the flowering date was delayed at the Owase station and several stations in south-eastern Japan, located in warm areas. Conversely, a few stations in cold regions indicated that recent flowering dates were earlier than those in the 1970s and 1980s, in addition to the trends shown by the first principal component.
