Page 339 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

aQuantitativeSOlUTION temperature and Degree-Days
In this chapter we describe different climates principally by using climographs to display annual regimes of temperature and pre- cipitation. Records of climate normals from Environment Canada (see climate.weather.gc.ca/climate_normals) include a total of
97 variables grouped in 18 categories. Beyond temperature and precipitation data, the list includes variables describing character- istics such as wind, humidity, pressure, and cloud amount.
Degree-days, derived from temperature records, is the num- ber of degrees that mean daily temperature is above or below a selected base value. There are three variants (Table AQS 10.1): cooling degree-days (CDD), growing degree-days (GDD), and heating degree-days (HDD). GDD for one day using a base value of 5°C (GDD5) is:
(beans), and 13°C (pumpkins). By keeping track of GDD accumu- lated during the growing season, harvest times can be planned.
Research has shown that one variety of canola, Bracissa napus, requires 1432–1557°C GDD (base 0°C) during the growing season to reach maturity, while Bracissa rapa requires only 1249–1382°C GDD. The latter variety can be planted in less favourable climates.
Cooling degree-days is calculated with the same equation used for growing degree-days, except that higher base values are used. CDD18 is a measure of the air conditioning requirements of buildings, while CDD24 is used as an index of heat stress.
Heating degree-days is calculated using the equation in re- verse. It is the number of degrees that mean daily temperature is less than the base value:
HDD = T − (Tmax + Tmin); if < 0 then HDD = 0 18 base(18) 2 18
HDD18 informs about heating requirements of buildings, assum- ing that if mean daily temperature is 18°C or higher, no heating is needed.
Degree-days is calculated from daily temperature records but it can be expressed as a long-term average, or climate, variable as shown in Table AQS 10.2.
In Canada, Windsor in southwestern Ontario (42°13’ N) has the highest average annual GDD values, 4002°C (base 0°C). At Prince Albert, Saskatchewan, 500 km north of Estevan and near the northern limit of farmland (53°13’ N), GDD0 = 2455°C annu- ally. Orchards and vineyards are found at Penticton (49°28’ N) in the Okanagan Valley, British Columbia, where GDD0 = 3673°C annually.
GDD = (Tmax + Tmin) − T 5 2
; if < 0 then GDD = 0 base(5) 5
where Tmax and Tmin are the maximum and minimum daily tempera- tures and Tbase(5) is the selected base value, 5°C. When the equation yields a value less than zero, the result is set to zero. For example, use the values for July 16, 2012, at Estevan, Saskatchewan, with the base value 5°C (see Table AQS 10.1) to calculate GDD (°C):
(28.1 + 16.9) 45
GDD5 = 2 −5= 2 −5=17.5°C
Growing degree-days is applied in agriculture. Crops require a certain amount of heat accumulated through the growing season to reach maturity. Different base values can be used, depending on the minimum temperature for plant growth; for example: base 0°C (cereals), 5°C (alfalfa, canola, general plant growth), 10°C
TaBlE aQS 10.1 Calculating Cooling, Growing, and Heating Degree-Days april 16
July 16
0.0 4.5
0.0
Oct. 16
0.0 0.0
8.1
Results are shown for maximum and minimum temperatures recorded at Estevan, Saskatchewan, on 3 days in 2012. (Station ID and name: 4012400, Estevan a.)
Daily Temperature (°C)
Maximum Minimum
1.5 −6.9
28.1 16.8
19.5 0.2
Cooling Degree-Days (°C)
Base 24 Base 18
0.0 0.0
20.7
Growing Degree-Days (°C)
Base 10 Base 5 Base 0
0.0 0.0 0.0
12.5 17.5 22.5
0.0 4.9 9.9
Heating Degree-Days (°C) Base 18
[environment Canada, climate.weather.gc.ca/index_e.html/]
TaBlE aQS 10.2 Long-Term Average Cooling, Growing, and Heating Degree-Days
Climate normals for 1981–2010 at Estevan, Saskatchewan (49°13’ N, 102°58’ W). The table shows mean total monthly and annual values. (Station ID and name: 4012400, Estevan a).
Month J F M a M J J a S O N D yr
Cooling Base 24 0 0 0 0 0 3 5 5 0 0 0 0 12 Degree-Days (°C) Base 18 0 0 0 0 6 28 67 59 9 0 0 0 170
Daily Temperature (°C)
Maximum Minimum
−8.2 −19.2
−5.3 −16.1
1.5 −9.1
12.2 −1.6
18.6 4.3
23 9.8
26.4 12.3
26.1 11.1
20 5.1
11.7 −1.6
1.3 −9.4
−6.5 −17.1
10.1 −2.6
Growing Degree-Days (°C)
Base 10 Base 5 Base 0
0 0 1
0 0 6
0
6 36
18
71 177
86 207 356
193 341 491
292 447 602
268 423 578
103 230 377
16
69 176
0
5 32
0 0 2
977 1799 2834
Heating Degree-Days (°C)
Base 18 982 811 676 382 209 77 23 39 172 401 662 925 5358
[environment Canada, climate.weather.gc.ca/index_e.html/]
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