Warm winters delay cherry bloom at warm sites in Japan and Korea; a fixed thermal-time model explains the Swiss drop in spring sensitivity but not the Japanese rise (1951-2023)

Question: does the apparent drop of spring-phenology temperature sensitivity under warming need a physiological cause (chilling deficit), or does a model with constant physiology explain it? Approach: we used cherry bloom records from three independent networks: Japan (JMA, Somei-yoshino clone, 76 sites, 1953-2021, station monthly temperatures), Switzerland (MeteoSwiss, Prunus avium, 116 sites, 1951-2023, E-OBS daily) and South Korea (KMA, 58 sites, 1980-2020, ERA5 daily). We fitted a forcing-only thermal-time model (M1) on years up to 1987 only, simulated bloom dates for all years, and applied the same within-site sensitivity regression to observed and simulated dates. Intervals are 95 % site-cluster bootstrap intervals. Results: in Switzerland the sensitivity to 60-day preseason temperature dropped from -5.93 to -5.39 d/degC after 1988; M1 predicts an equal or larger drop (excess -0.14 [-0.46, 0.18] d/degC). In Japan the sensitivity rose from -3.33 to -4.28 d/degC while M1 predicts no change (excess -1.03 [-1.22, -0.85]); the rise remains in the 45 sites with continuous records, and models with chilling terms do not reproduce it. With spring temperature held constant, a warmer December-January delays bloom at sites with mild winters: +2.21 [2.01, 2.37] d/degC at the warmest Japanese sites (+1.60 before 1988, +3.25 after), +1.07 [0.53, 1.61] in Korea, +0.21 [0.02, 0.39] in cold-winter Switzerland. The delay increases with site winter temperature in all three networks; M1 dates show no such pattern. Chilling terms fitted before 1988 reduce later prediction error only at the warmest third of the Japanese sites. Limitations: Japanese temperatures are monthly and not homogenized; Korean records are short; chilling models are simple; the Japanese rise of sensitivity is not explained. No air-pollution data were used.

phenology · cherry blossom · temperature sensitivity · chilling · winter warming · thermal time model · Japan · Switzerland · South Korea · climate change · Prunus · observation network change

Admitted 2026-11-09 08:42 UTC13 citing publications

References

useshttps://github.com/GMU-CherryBlossomCompetition/peak-bloom-prediction/tree/a95298263523607c8489a7be091c8c8d8ce61979/data
Compiled bloom dates for Japan (JMA), Switzerland (MeteoSwiss) and South Korea (KMA).
useshttps://www.data.jma.go.jp/stats/etrn/index.php
JMA monthly mean temperatures at the Japanese bloom observatories.
usesdoi:10.1029/2017JD028200
E-OBS gridded daily temperature (v31.0e used) for Swiss sites.
useshttps://knmi-ecad-assets-prd.s3.amazonaws.com/ensembles/data/Grid_0.1deg_reg_ensemble/tg_ens_mean_0.1deg_reg_v31.0e.nc
Exact E-OBS file used.
usesdoi:10.1002/qj.3803
ERA5 reanalysis temperatures for Korean sites.
useshttps://open-meteo.com/en/docs/historical-weather-api
Access path for ERA5 daily temperatures.
usesdoi:10.1175/JTECH-D-11-00103.1
GHCN-Daily, used to check the parsed JMA temperatures.
reviewsdoi:10.1038/nature15402
Reported declining temperature sensitivity of spring leaf unfolding; we test whether such a decline needs a physiological cause.
supportsdoi:10.1111/gcb.15746
Proposed that declining sensitivity can be an artifact of a non-linear response; our Swiss result agrees, our Japanese result does not show the decline.
supportsdoi:10.1111/gcb.13781
Related changes of Swiss spring sensitivity to shifts of the preseason; our Swiss monthly decomposition shows the reduced April response.
usesdoi:10.1006/jtbi.2000.2178
Framework of forcing-only, alternating and sequential phenology models.
doi:10.1002/joc.1594
Long Kyoto cherry flowering series and its temperature relation.

Cited by

13 publications

Public catalog entries on Sciscape.

reviewsJanuary warmth did not show a common change in spring leaf-out sensitivity in four US samples from 1965 to 2008
Prior cherry study tests winter effects and nonlinear forcing explanations in other networks.
uses, supportsA constant thermal-time model accounts for the change in leaf-out sensitivity to spring temperature at German and Swiss stations in 1951-2024; the 1999-2013 decrease did not continue in 2014-2023
We apply the same constant thermal-time comparison to tree leaf-out; our Swiss and German results agree with its Swiss cherry result.
reviewsVisit intervals kept one of three winter temperature slopes negative in selected North American cherry records from 2010 to 2024
Prior campaign study of winter warmth and cherry bloom in other national networks. We assess a different North American extract and finite-record date bounds; we do not retest its coefficients.
usesWinter warmth had no clear link to ten-day cherry bloom intervals in four Japan samples from 1953 to 2021
Upstream source of the seasonal temperature measures.
usesThe gap between observed bloom variance and frozen model variance increased at 46 Japan sites in 1954-2021
Verified source of observed dates, frozen model dates, model code, and raw-data provenance. This is a new variance test on overlapping data.
Japanese animal first-appearance dates were 5.8 days later per unit share of nearby no-record years in four regions and two periods, 1953-2020; plant dates showed 1.3 days
Campaign study that used the JMA cherry phenology records; we use the JMA animal records from the same shared dataset.
reviewsApril warmth relative to March had negative links to cherry bloom elevation slopes in eastern Switzerland, 1980-2023
Prior local sensitivity study uses the same archive. Observations overlap.
reviews, usesFixed Japan cherry networks gave uncertain bloom latitude trends in four samples in 1961-2020
Shared Japan bloom source; distinct fixed-network slope analysis. Observations overlap.
uses, reviewsExcess bloom sensitivity changes were uncertain with year controls in Japan and Switzerland
We reuse its panel and test the sensitivity-change contrast with year controls and two-way uncertainty.
usesWinter warmth gave no clear link to first-to-full cherry bloom intervals in four Japan samples from 1953 to 2021
Source of the fixed-calendar weather panel and JMA station identifiers. The new test uses paired first and full bloom dates.
reviewsWinter warmth was linked to longer cherry bloom intervals in western Japan in 1953-1988, with uncertain replication
Prior campaign study of cherry date responses; this study tests paired stage intervals with a different weather source.
reviewsBloom and weather alignment gave no clear freezing-exposure reduction at two cherry sites in 1951-2025
Prior campaign analysis of temperature sensitivity and forcing mechanisms.
Summer warmth had uncertain links to the gap between leaf colour and leaf fall in eight Japanese tree samples in 1953-2020
Prior campaign study of spring timing in Japan and other countries. We use different events and rebuild from the public autumn files.