Table 1. Thirty-year historic climatic averages from regions where the effects of plant selection on green roof performance has been researched (except heating and cooling degree days which are averages from 2007-2009)[55]-[60].
| Daily Temp (°C) | Heating Degree Daysa | Cooling Degree Daysb | Rainfall (mm) | Sunlight (hrs) | Relative humidity (%) | |||||
| City | Month | Min | Max | Mean | Monthly Sum | Monthly Sum | Monthly Sum | Daily Avg | AM | PM |
| Halifax, CAN | May | 5.5 | 14.1 | 9.8 | 196.0 | 7.3 | 118.1 | 6 | 76.0 | 62.0 |
| June | 10.5 | 19.4 | 15.0 | 59.3 | 21.7 | 108 | 7 | 77.0 | 63.0 | |
| July | 14.2 | 22.9 | 18.6 | 17.3 | 69.0 | 105.9 | 8 | 81.0 | 64.0 | |
| August | 14.8 | 23.0 | 18.9 | 15.7 | 63.7 | 98.3 | 7 | 82.0 | 65.0 | |
| September | 11.4 | 19.0 | 15.2 | 73.7 | 17.0 | 107.1 | 6 | 82.0 | 65.0 | |
| Avg. | 11.3 | 19.9 | 15.5 | – | – | – | 7.0 | 79.0 | 63.5 | |
| Total | – | – | – | 362.0 | 178.7 | 537.4 | – | – | – | |
| Source | 1 | 1 | 1 | 5 | 5 | 1 | 3 | 3 | 3 | |
| Toronto, CAN [52] | May | 9.9 | 18.5 | 14.2 | 125.7 | 9.3 | 73.3 | 7 | 73.0 | 55.0 |
| June | 14.8 | 23.5 | 19.2 | 23.3 | 46.0 | 71.5 | 9 | 78.0 | 58.0 | |
| July | 17.9 | 26.4 | 22.2 | 8.3 | 68.7 | 67.5 | 9 | 79.0 | 56.0 | |
| August | 17.3 | 25.3 | 21.3 | 2.3 | 99.3 | 79.6 | 8 | 83.0 | 58.0 | |
| September | 13.2 | 20.7 | 17 | 20.0 | 38.7 | 83.4 | 7 | 87.0 | 60.0 | |
| Avg. | 14.6 | 22.9 | 18.8 | – | – | – | 8 | 80 | 57.4 | |
| Total | – | – | – | 179.6 | 262.0 | 375.3 | – | – | – | |
| Source | 1 | 1 | 1 | 5 | 5 | 1 | 3 | 3 | 3 | |
| Vancouver, CAN [53] | May | 9.5 | 16.8 | 13.2 | 107.7 | 6.3 | 86.7 | 8 | 88.0 | 63.0 |
| June | 12.2 | 19.6 | 15.9 | 46.7 | 16.7 | 69.9 | 7 | 87.0 | 65.0 | |
| July | 14.1 | 22.0 | 18.1 | 11.7 | 52.0 | 49.1 | 9 | 89.0 | 62.0 | |
| August | 14.4 | 22.3 | 18.3 | 14.7 | 34.7 | 48.3 | 8 | 90.0 | 62.0 | |
| September | 11.6 | 19 | 15.4 | 57.3 | 9.0 | 71 | 6 | 92.0 | 72.0 | |
| Avg. | 12.4 | 19.9 | 16.2 | – | – | – | 7.6 | 89.2 | 64.8 | |
| Total | – | – | – | 238.1 | 118.7 | 325 | – | – | – | |
| Source | 1 | 1 | 1 | 5 | 5 | 1 | 3 | 3 | 3 | |
| Portland, USA [54] | May | 8.6 | 19.3 | 13.9 | 75.3 | 40.3 | 60.5 | 8 | 70.0 | 58.0 |
| June | 11.4 | 22.6 | 17.1 | 31.3 | 54.3 | 40.4 | 10 | 73.0 | 60.0 | |
| July | 13.8 | 26.3 | 20.1 | 8.7 | 141.7 | 18.3 | 10 | 75.0 | 63.0 | |
| August | 14.1 | 26.5 | 20.3 | 9.3 | 113.0 | 23.6 | 9 | 78.0 | 62.0 | |
| September | 11.4 | 23.7 | 17.5 | 33.0 | 70.0 | 41.9 | 8 | 79.0 | 63.0 | |
| Avg. | 11.9 | 23.7 | 17.8 | – | – | – | 9 | 75 | 61.2 | |
| Total | – | – | – | 157.6 | 419.3 | 184.7 | – | – | – | |
| Source | 2 | 2 | 2 | 5 | 5 | 2 | 3 | 3 | 3 | |
| Lansing, USA [27] | May | 7.1 | 20.8 | 13.9 | 100.3 | 33.3 | 68.8 | 8 | 73.0 | 59.0 |
| June | 12.4 | 25.6 | 19.0 | 21.7 | 100.7 | 91.4 | 10 | 74.0 | 58.0 | |
| July | 14.7 | 27.8 | 21.3 | 15.0 | 118.7 | 68.1 | 9 | 73.0 | 53.0 | |
| August | 13.9 | 26.5 | 20.2 | 15.0 | 122.0 | 87.9 | 9 | 77.0 | 53.0 | |
| September | 9.4 | 22.2 | 15.8 | 42.7 | 60.7 | 88.4 | 8 | 80.0 | 59.0 | |
| Avg. | 11.5 | 24.6 | 18.0 | – | – | – | 8.8 | 75.4 | 56.4 | |
| Total | – | – | – | 94.7 | 435.4 | 404.6 | – | – | – | |
| Source | 2 | 2 | 2 | 5 | 5 | 2 | 3 | 3 | 3 | |
| Sheffield, UK [31] | May | 6.7 | 15.8 | 11.3 | 157.7 | 2.3 | 61.9 | 6 | 71.0 | – |
| June | 9.6 | 18.3 | 14.0 | 90.3 | 6.3 | 62.6 | 6 | 71.0 | – | |
| July | 11.9 | 20.9 | 16.4 | 60.0 | 9.0 | 52.8 | 6 | 74.0 | – | |
| August | 11.7 | 20.4 | 16.1 | 51.0 | 7.3 | 66.7 | 5 | 77.0 | – | |
| September | 9.6 | 17.1 | 13.3 | 101.0 | 1.3 | 63.2 | 4 | 80.0 | – | |
| Avg. | 9.9 | 18.5 | 14.2 | – | – | – | 5.4 | 74.6 | – | |
| Total | – | – | – | 460.0 | 26.2 | 307.2 | – | – | – | |
| Source | 4 | 4 | 4 | 5 | 5 | 4 | 3 | 3 | – | |
| Berlin, GER [41] | May | 8.2 | 18.6 | 13.5 | 77.7 | 28.7 | 52.5 | 8 | 80.0 | 57.0 |
| June | 11.4 | 21.8 | 16.7 | 34.3 | 51.3 | 65.5 | 8 | 80.0 | 58.0 | |
| July | 12.9 | 23.1 | 17.9 | 18.7 | 73.7 | 46.0 | 8 | 84.0 | 61.0 | |
| August | 12.4 | 22.8 | 17.2 | 20.7 | 71.0 | 55.6 | 7 | 88.0 | 61.0 | |
| September | 9.4 | 18.7 | 13.5 | 75.7 | 16.7 | 49.7 | 6 | 92.0 | 65.0 | |
| Avg. | 10.9 | 21.0 | 15.8 | – | – | – | 7.4 | 84.8 | 60.4 | |
| Total | – | – | – | 227.1 | 241.4 | 269.3 | – | – | – | |
| Source | 6 | 6 | 6 | 5 | 5 | 6 | 3 | 3 | 3 |
a
Heating degree days calculated as the number of days or fraction thereof for which temperatures were below 15°C times (15 (°C) – temperature).
b
Cooling degree days calculated as the number of days or fraction thereof for which temperatures were above 18°C times (temperature (°C) - 18).