Horse chestnut Aesculus hippocastanum
Expected first-bloom dates for spring 2027 in 16 cities.
| City | Status | Expected start | Likely range | Label | Model MAE (d) | Climatology MAE (d) | Obs. years |
|---|---|---|---|---|---|---|---|
| Berlin | Season over | ~30 Apr 2027 | 22 Apr – 8 May | validated | 2.47 | 5.42 | 35 |
| Hamburg | Season over | ~6 May 2027 | 24 Apr – 11 May | validated | 3.66 | 6.06 | 35 |
| Munich | Season over | ~4 May 2027 | 25 Apr – 10 May | validated | 2.43 | 5.82 | 35 |
| Cologne | Season over | ~24 Apr 2027 | 16 Apr – 6 May | validated | 3.47 | 5.35 | 35 |
| Frankfurt | Season over | ~24 Apr 2027 | 15 Apr – 6 May | validated | 2.94 | 5.11 | 35 |
| Stuttgart | Season over | ~26 Apr 2027 | 15 Apr – 5 May | validated | 2.57 | 5.44 | 35 |
| Dresden | Season over | ~30 Apr 2027 | 23 Apr – 8 May | validated | 2.26 | 5.99 | 35 |
| Hanover | Season over | ~30 Apr 2027 | 20 Apr – 9 May | validated | 2.53 | 6.49 | 35 |
| Leipzig | Season over | ~29 Apr 2027 | 21 Apr – 8 May | validated | 2.43 | 5.84 | 35 |
| Nuremberg | Season over | ~1 May 2027 | 22 Apr – 8 May | validated | 2.54 | 6.42 | 35 |
| Stockholm | Season over | ~26 May 2027 | 21 May – 1 Jun | approximate | n/a | n/a | 2 |
| Uppsala | Season over | ~24 May 2027 | 19 May – 29 May | approximate | n/a | n/a | 1 |
| Gothenburg | Season over | ~18 May 2027 | 10 May – 23 May | approximate | n/a | n/a | 2 |
| Malmö | Season over | ~14 May 2027 | 8 May – 20 May | approximate | n/a | n/a | 2 |
| Linköping | Season over | ~22 May 2027 | 13 May – 26 May | approximate | n/a | n/a | 0 |
| Örebro | Season over | ~22 May 2027 | 15 May – 27 May | approximate | n/a | n/a | 2 |
Backtest (leave-one-year-out)
| Country | City-years | Model MAE | Simple climatology MAE | Within ±5 days |
|---|---|---|---|---|
| Germany | 350 | 2.73 d | 5.79 d | 88% |
| Sweden | not enough open observations for a local backtest | |||
Model parameters
- Germany: sum of daily mean temperature above 4 °C from 1 Mar; bloom when the sum reaches 231 °C·days (fitted on 350 city-years)
- Sweden: sum of daily mean temperature above 4 °C from 1 Mar; bloom when the sum reaches 231 °C·days (parameters transferred from Germany — unchecked)
MAE = mean absolute error in days. “Climatology” = just using the average date of the other years. Details and limits: How it works.