The significance of mining phenological data from the early 20th century: Insights from more than 100 years of cherry blossom phenology in Kumagaya, Japan

This study aims to demonstrate the importance of mining historical phenological records from the early 20th century in Japan by using more than a century of nearly continuous records of first flowering dates (FFD) and full bloom dates (FBD) of cherry trees in Kumagaya. Over the past 100 years, FFD and FBD in Kumagaya have advanced by 10.5 and 12.1 days, respectively, while the period between them has not changed. These findings suggest that although the optimal timing for hanami (cherry blossom viewing) has shifted earlier, the impact on the duration of the hanami season is likely to be minor. Phenological records spanning more than a century provide invaluable insights for assessing the long-term sustainability of cultural ecosystem services. The 31-year moving linear regression (MLR) analyses used here revealed a wide range of trends from +0.1 to –0.3 days/year for FFD and from +0.2 to −0.3 days/year for FBD, highlighting the importance of data accumulation and including records from the early 20th century. The 51-year MLR analyses of FFD and FBD revealed a marked intensification of phenological trends in recent decades, suggesting that these trends reflect the combined effects of climate change and urbanization in Kumagaya. Therefore, including phenological records from the early 20th century is of particular value for disentangling the pure climatic effects of global warming from those associated with urban development in Japan. The mining of phenological records across Japan during the early 20th century will also become increasingly important for sustaining cultural ecosystem services.