An attempt is made to estimate blooming dates of Prunus yedoensis for 21 meteorological stations in Japan by using DTS (the number of days transformed to standard temperature). The starting date for computation at each station is determined by correlation analysis. At many stations the date lies between 40 and 55th day from January 1st.
The number of days transformed to a standard temperature (in this study 25°C is used) at each station is computed by adding characteristic temperature of each day from a starting date to blooming date for various temperature characteristic (Ea). The estimated blooming date is the date when accumulated value of DTS reached at that of mean observed blooming date for the site.
It is found that 17kcal mol-1 for Ea gives minimum error when averaged over all sites. Using this Ea and D2 which is the starting date determined from error analysis, computations are made to estimate blooming dates at each station between 1961 and 1985. It is shown that at stations in Hokkaido and Tohoku districts, RMS errors between the observed and the calculated blooming dates fall between 1 and 2 days. At stations in other areas, the errors range between 2 and 3, except for Hachijo where it becomes 6.7 days. The large error at this southernmost station seemed to be attributed to year to year change of degrees of rest completion of Prunus yedoensis, which affect effectiveness of temperature just before blooming.
