Satellite data analysis shows earlier spring leaf flush in Japan caused by high temperatures in 2023 and 2024

Average day of year (DOY) of spring leaf flush (SOS: Start of Season) from 2018 to 2022 derived from satellite data (GCOM-C/SGLI). Credit: Scientific Reports (2025). DOI: 10.1038/s41598-025-94623-9

Researchers at the University of Tsukuba estimated Japan’s spring leaf flush dates in recent years using data from the Second-generation Global Imager (SGLI) sensor onboard the Japan Aerospace Exploration Agency’s (JAXA) Global Change Observation Mission-Climate (GCOM-C) satellite.

Their analysis revealed that in 2023 and 2024, years characterized by exceptionally high spring temperatures, leaf flush occurred significantly earlier than usual, indicating that elevated temperatures linked to climate change are affecting Japanese ecosystems.

Previous research had predicted that global warming would lead to earlier spring flowering and leaf flush. This study used satellite-based observations to verify that this phenomenon occurred under the unusually high spring temperatures of 2023 and 2024.

Based on data from JAXA’s GCOM-C satellite, researchers estimated the start of season (SOS), which is the onset of spring leaf flush, for the period 2018–2024. In 2023, SOS occurred three to seven days earlier than the 2018–2024 average in the Kanto and Chubu regions. In 2024, similar shifts were observed in the Hokuriku, Tohoku, and Hokkaido regions.

Examples of digital camera images. The bottom numbers represent day of year (DOY). Credit: Scientific Reports (2025). DOI: 10.1038/s41598-025-94623-9

Notably, in the area surrounding the Shirakami Mountains, a UNESCO World Natural Heritage site, SOS in 2024 was approximately nine days earlier than the multi-year average. These deviations were more pronounced in years with elevated spring temperatures, suggesting that global warming and other temperature-increasing factors are exerting broad ecological impacts across Japan.

The study, published in Scientific Reports, also examined the relationship between SOS and spring air temperature (February to April), finding that a 1 K rise in temperature advances SOS by an average of 4.4 days. When applied to future climate scenarios, this corresponds to SOS occurring approximately seven days earlier under RCP 2.6 (representing the lowest temperature increase scenario) and about 21 days earlier under RCP 8.5 (the highest temperature increase scenario).

Understanding how ecosystems respond to such temperature increases is essential for assessing the ecological impacts of future climate change, as earlier SOS can impose various stresses on ecosystems. As extreme weather events are expected to become more frequent, continued satellite-based monitoring and expansion of field observation networks will be critical for tracking and mitigating these effects.

More information:
Yuki Mizuno et al, Impact of high temperature in 2023 and 2024 on spring leaf flush phenology in Japan derived by GCOM-C satellite, Scientific Reports (2025). DOI: 10.1038/s41598-025-94623-9

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University of Tsukuba

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Satellite data analysis shows earlier spring leaf flush in Japan caused by high temperatures in 2023 and 2024 (2025, April 23)
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