Temperature models fitted to 1952–1990 German leaf-out data predict 1991–2025 leaf-out 1.7 to 5.1 days too late for seven tree species
Question: can temperature-only models of spring leaf-out, fitted to past data, predict later leaf-out when the climate is warmer? Approach: we used the Deutscher Wetterdienst volunteer phenology network (7 tree species, 94,000 to 153,000 station-years each, 1952-2025) and the 1 km HYRAS-DE daily temperature grid. We fitted five model types (linear preseason, thermal time, chill-forcing, a flexible model on 16-day mean temperatures, and thermal time from 1 January) on 1952-1990 and predicted 1991-2025. Result: all four models that fit the calibration years well predicted leaf-out too late in 1991-2025. The mean residual was -1.7 to -5.1 days, and all 28 species x model 90% intervals were below zero. The flexible model did not explain 12% (larch) to 58% (ash) of the 10 to 12 day observed advance between 1952-1990 and 2011-2025. The excess stayed for persistent stations, in pairs of years with similar temperature (-1.6 to -5.0 days at the same stations), in former East and West Germany, at all elevations, with CRU TS temperature (0.09 K difference in warming), and with global radiation added (0.0 to 0.4 days change). Flowering onset of 8 of 9 other wild plants was also earlier than predicted. The thermal-time model with a fixed 1 January start had the opposite bias, so the sign depends on model structure. The shift has a step-like form near 1989-1993, when the all-German observation programme started. But transfers inside each programme period also gave -1.5 and -1.7 days. Limitation: the data cannot separate observer or programme effects, local microclimate change that the grid does not show, and drivers that are not temperature. Year-resampling intervals do not include serial correlation.
phenology · leaf-out · temperature sensitivity · out-of-sample validation · thermal time · Deutscher Wetterdienst · HYRAS · climate change · model transfer · Germany · trees · flowering
References
5- doi:10.1016/j.agrformet.2015.11.007
Earlier evaluation of leaf-out models on PEP725 data; found compressed interannual variation.
- doi:10.1038/nature15402
Reported declining apparent temperature sensitivity of leaf unfolding in Europe.
- doi:10.1038/s44383-025-00004-6
Interpretation of apparent phenological temperature sensitivity under warming.
- usesdoi:10.1007/s00704-020-03388-w
HYRAS daily temperature grid used as model input.
- usesdoi:10.1038/s41597-020-0453-3
CRU TS monthly temperature used as independent check of warming.
Cited by
6 publicationsPublic catalog entries on Sciscape.
- Thermal-time models fitted to 1960–1990 air temperature predict 44–64% of the later lake ice freeze-up in 1991–2026, and 73–84% of the earlier break-up, at lakes in Finland and the LIAG database
Same out-of-sample design (temperature models fitted to early decades) for tree leaf-out.
- A degree-day model with gridded air temperature, fitted to 1951–1985 only, predicts 85–91% of the 5.7-day earlier ice-off at 100 Northern Hemisphere lakes in 1986–2020
Out-of-sample test of temperature models fitted to early decades of phenology data.
- supportsIn 31 German spring phases, temperature sensitivity did not decrease from 1952–1966 to 2012–2025, and the 1980–1994 to 1999–2013 decrease agrees with a forcing-only model
Independent replication with the same DWD and HYRAS sources but different code, 31 phases and a 1985 training cutoff: observed dates after the training years are earlier than forcing-model forecasts.
- supportsIn 31 German spring phases, temperature sensitivity did not decrease from 1952–1966 to 2012–2025, and the 1980–1994 to 1999–2013 decrease agrees with a forcing-only model
Independent replication with the same DWD and HYRAS sources but different code, 31 phases and a 1985 training cutoff: observed dates after the training years are earlier than forcing-model forecasts.
- Thermal-time models fitted to 1952–1987 German phenology predict 1988–2026 dates of 32 spring phases 3.3 days too late, and the error does not increase with station warming
[Legacy relation: reproduces] Same network and question for seven tree species (1952-1990 to 1991-2025). We reproduce the late-prediction bias with separate code for 32 phases, add a cross-station warming test and a placebo split, and find a continuing post-step trend where it reported a nearly flat one.
- In Germany in 1951–2025, tree leaf-out and fruit-tree flowering moved earlier by 2.1 days per decade and the last −2 °C frost by 1.3 days, but frost after onset did not increase significantly
Related analysis of German leaf-out advance in the same DWD data.