Estimation of Blooming Date for Prunus Yedoensis Using DTS Combined with Chill-Unit Accumulations

Abstract

Blooming dates of Prunus yedoensis at 38 sites are estimated by using “the number of days transformed to standard temperature (hereafter referred as DTS)” for the 25 year period starting 1961. The sites are all located at or in the vicinity of the meteorological observatories of Japan Meteorological Agency. The standard temperature for DTS in this study is chosen 25°C, for the temperature characteristic Ea, a value [71.1kJ mol-1] is used for all stations. Both of these values are the same as those in our previous paper, although CGS unit was used before. It is shown that by this first estimation RMS errors of estimated blooming dates fell within a range 1-3 days except for stations in regions of southern coasts of Kyushu Is. and Izu Is. An attempt of reducing errors, in the first place, readjustment of accumulated DTS was made. This enable us to reduce RMS error up to 0.5 days from the previous computations. But this approach was not very effective at southern stations. Large RMS error in these warm regions seemed to be due to incomplete transition of rest break or large interannual variation of this process. An adjustment of estimation of blooming date at southern sites is made by applying the concept of chill-unit which is the weighted hour corresponding to the effectiveness of chilling to rest completion. It is shown that this procedure reduced RMS error of blooming dates to 2.32 days from 6.64 days at Hachijo Is., and at all stations in warm regions the error reduced to about 2 days. © 1990, The Society of Agricultural Meteorology of Japan. All rights reserved.