Lilac Syringa vulgaris
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 | ~1 May 2027 | 23 Apr – 7 May | validated | 2.47 | 6.11 | 35 |
| Hamburg | Season over | ~6 May 2027 | 24 Apr – 15 May | validated | 3.13 | 6.31 | 35 |
| Munich | Season over | ~6 May 2027 | 25 Apr – 11 May | validated | 3.09 | 5.93 | 35 |
| Cologne | Season over | ~22 Apr 2027 | 11 Apr – 6 May | validated | 3.5 | 6.17 | 35 |
| Frankfurt | Season over | ~22 Apr 2027 | 13 Apr – 5 May | validated | 3.7 | 6.33 | 35 |
| Stuttgart | Season over | ~23 Apr 2027 | 13 Apr – 4 May | validated | 2.29 | 5.93 | 35 |
| Dresden | Season over | ~1 May 2027 | 23 Apr – 7 May | validated | 2.26 | 5.94 | 35 |
| Hanover | Season over | ~30 Apr 2027 | 17 Apr – 8 May | validated | 2.96 | 6.17 | 35 |
| Leipzig | Season over | ~28 Apr 2027 | 19 Apr – 7 May | validated | 2.56 | 6.14 | 35 |
| Nuremberg | Season over | ~2 May 2027 | 22 Apr – 8 May | validated | 2.54 | 6.55 | 35 |
| Stockholm | Season over | ~25 May 2027 | 20 May – 31 May | validated | 4.18 | 4.71 | 11 |
| Uppsala | Season over | ~24 May 2027 | 17 May – 28 May | validated | 3 | 4.09 | 12 |
| Gothenburg | Season over | ~17 May 2027 | 9 May – 22 May | validated | 4.67 | 6.11 | 12 |
| Malmö | Season over | ~12 May 2027 | 7 May – 19 May | approximate | 5.58 | 7.1 | 6 |
| Linköping | Season over | ~21 May 2027 | 12 May – 25 May | validated | 2.31 | 3.77 | 8 |
| Örebro | Season over | ~22 May 2027 | 14 May – 27 May | validated | 2.07 | 3.46 | 14 |
Backtest (leave-one-year-out)
| Country | City-years | Model MAE | Simple climatology MAE | Within ±5 days |
|---|---|---|---|---|
| Germany | 350 | 2.85 d | 6.16 d | 87% |
| Sweden | 63 | 3.48 d | 4.69 d | 81% |
Model parameters
- Germany: sum of daily mean temperature above 5 °C from 1 Feb; bloom when the sum reaches 197 °C·days (fitted on 350 city-years)
- Sweden: sum of daily mean temperature above 4 °C from 1 Mar; bloom when the sum reaches 222 °C·days (fitted on 63 city-years)
MAE = mean absolute error in days. “Climatology” = just using the average date of the other years. Details and limits: How it works.