It has been known that cherry trees in the central area of a large city come into blossom earlier than those in the suburbs. One of the main causes of this advancement of blooming dates is urban warming. The purpose of this paper is to show the relationship between the amount of urban warming (ΔTu), and the amount of advancement of blooming dates (ΔBDu). Data used in this study are official records of blooming dates of Prunus yedoensis (the most popular species of cherry trees in Japan) at stations of the Japan Meteorological Agency (JMA) and daily mean temperatures at these stations.
In oder to obtain ΔBDu which is assumed to be entirely temperature dependent, it is necessary to estimate blooming dates from temperature data. This could be made by the method reported in our previous paper (Omoto and Aono, 1989). It enables us to relate deviation of blooming dates of a particular year from mean blooming dates (ΔBD) with deviation of temperature from the normal (ΔTa). The linear relationship between ΔBD and ΔTa found at each site suggests that we can replace these parameters by ΔBDu and ΔTu respectively. The evaluation of ΔTu is made by the method proposed by Omoto and Hamotani (1979). It is pointed out that the proportional constants β at various stations differ systematically such that the earlier the mean blooming date, the smaller the value of β.
Nevertheless there are several sources of error in the computations of ΔBDu and ΔTu, comparisons between variations of actual and estimated blooming dates in several large cities in Japan indicate that the present method gives reasonable estimation.
