Reconstruction of April temperatures in Kyoto, Japan, since the fifteenth century using the floral phenology of herbaceous peony and rabbit-ear iris.

Abstract

We reconstructed April mean temperatures in Kyoto since the fifteenth century by investigating historical documents such as diaries and chronicles and compiling phenological data series of the full bloom date for herbaceous peony. In order to fill gaps in phenological data series, we used the full bloom date of rabbit-ear iris, an herbaceous plant that flowers at about the same time of the year as an herbaceous peony. We obtained floral phenological data covering a total of 278years. Calibration using modern temperature data showed herbaceous peony phenology to be the preferred data source for April temperature estimation. Variations in the reconstructed April temperatures in Kyoto were synchronous with changes in the solar cycle. In particular, April temperatures were about 2℃ lower than at present around the ends of the Spoerer and Maunder grand solar minima, from 1550 to 1590 and from 1690 to 1730, respectively. In addition, the reconstructed April temperatures suggested a time lag in the climate response to solar activity changes that was about 10years longer than the previously estimated lags in the responses of wintertime and March temperatures. However, further research is needed to accurately quantify this time lag.