The DTS accumulation model for predicting the flowering date of Japanese pear tree in Japan

In order to estimate the flowering time, the heat accumulation model with an index referred to as DTS (the number of days transformed to standard temperature) is used in this study. The flowering date of Japanese pear trees (evs. Kousui, Housui and Nijisseiki) was monitored at 21 experiment stations in various pear growing regions throughout Japan. A DTS accumulation model based on air temperature data was developed and applicable in most stations. The model was verified using the root mean square error (RMSE) for difference in days between the actual and estimated flowering dates. The RMSE in warm (or southwest) regions was larger than other regions in Japan. Analysis using DTS indicated that the estimated flowering dates were slightly ahead of the actual flowering dates at most stations. It was assumed that urban warming around the meteorological observatories could cause the same error in estimation. To test this hypothesis, the influence of the urban warming on flowering dates at Utsunomiya city was evaluated by the DTS accumulation model. However, the present method might elucidate a marked difference between actual and estimated flowering dates of late years in some measure.