Climate

Climate Types

The following system of symbols (called the Trewartha Modification of the Koppen Classification System) is one that is used to classify various types of climates:

A — Tropical forest climates with no cool season; fairly constant warm temperature
Af:constantly moist; rainfall all through the year
Aw:distinct dry season in winter (Savanna).
Am:monsoon rain; short, dry season, but with sufficient total rainfall to support rain forest
B — Dry climates (precipitation variable and effectiveness dependent upon the rate of evaporation, which in turn, varies directly with temperature)
Bs:semi-arid climates (Steppe)
Bw:desert and arid climates (Wuste)
 h:(heiss) tropical or low-latitude — hot (heiss = German for “hot”)
 k:(kalt) cold or middle-latitude (kalt = German for “cold”)
C — Mesothermal (warm temperature) forest climates with cooler but mild winters (coldest month above 32° F [0° C]; warmest month above 50° F [10° C] (meso = middle; thermo = heat)
Cf:no distinct dry season
Cw:dry season in winter
Cs:dry season in summer (Mediterranean type — medi = middle; terra = earth, land)
 a:hot summer (warmest month over 71.6° F [22° C])
 b:cool summer (warmest month under 71.6° F [22° C])
 c:cool, short summer; less that 4 months over 50° F [10° C]
D — Microthermal (cold, snowy) forest climates with severe winters (coldest month below 32° F; warmest month above 50° F [10° C])
Df:no dry season
Dw:dry winters
 a:hot summer (warmest month over 71.6° F [22° C])
 b:cool summer (warmest month under 71.6° F [22° C])
 c:cool, short summer; less that 4 months over 50° F [10° C]
E — Polar climates with no warm season (warmest month below 50° F [10° C])
Et:tundra climate (warmest month below 50° F [10° C], but above 32° F [0° C])
Ef:perpetual frost (all months below 32° F [0° C]); such climates persist only over the permanent ice caps


Problem:

Consider the weather data for the cities listed in Table 1. Classify the climatic types of these twelve cities using the Koppen symbols (letters).

Table 1. Weather in Selected Cities
(temperature in ° F, rainfall in inches)
City T/R Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Type?
1 Athens, Greece T
R		 50
2.2		 50
1.5		 52
1.4		 60
0.9		 66
0.8		 74
0.6		 81
0.3		 80
0.4		 73
0.6		 67
1.7		 67
2.8		 52
2.5
2 Aukland, New Zealand
(seasons reversed)
 T
R		 67
2.7		 67
3.1		 66
3.0		 61
3.4		 57
4.6		 54
4.9		 52
5.0		 52
4.2		 55
3.6		 57
3.7		 60
3.3		 64
2.9
3 Barrow, Alaska, USA T
R		 –17
0.2		 –14
0.2		 –14
0.1		 0
0.1		 21
0.2		 36
0.3		 40
0.9		 39
0.7		 31
0.5		 16
0.6		 9
0.3		 –15
0.3
4 Boston, Mass., USA T
R		 27
3.4		 28
3.1		 35
3.6		 45
3.7		 57
2.9		 68
3.2		 71
3.3		 69
3.3		 63
3.5		 52
2.8		 41
2.9		 32
3.4
5 Cincinnati, Ohio, USA T
R		 28
2.6		 32
2.7		 43
4.2		 53
3.8		 63
4.3		 71
3.8		 75
4.2		 74
3.4		 67
2.9		 55
2.9		 44
3.5		 34
3.2
6 Cuyaba, Brazil
(seasons reversed)
 T
R		 81
9.8		 81
8.3		 81
8.3		 81
4.0		 79
2.1		 77
0.3		 76
0.2		 78
1.1		 80
2.0		 82
4.5		 82
5.9		 81
8.1
7 Delhi, India T
R		 58
0.8		 62
0.7		 74
0.5		 86
0.4		 90
0.6		 90
3.1		 86
8.1		 85
7.9		 84
4.4		 79
0.3		 68
0.1		 60
0.5
8 Georgetown, Guyana T
R		 79
8.5		 79
6.0		 80
6.8		 80
6.4		 81
10.0		 80
9.9		 80
10.0		 82
6.5		 83
3.1		 82
2.9		 82
5.9		 81
10.0
9 Monterrey, Mexico T
R		 58
0.8		 62
0.7		 68
0.8		 74
1.3		 79
1.3		 82
3.0		 82
2.3		 83
2.4		 78
5.2		 72
3.0		 64
1.5		 57
0.8
10 Moscow, USSR T
R		 14
1.3		 17
1.2		 25
1.4		 39
1.4		 55
1.8		 61
2.7		 66
3.2		 62
3.1		 49
2.2		 40
2.1		 28
1.7		 19
1.6
11 Odessa, USSR T
R		 26
1.2		 29
0.9		 37
1.1		 47
0.9		 60
1.1		 68
2.2		 73
1.7		 70
1.4		 62
1.2		 52
1.5		 40
1.1		 32
1.2
12 Phoenix, Ariz, USA T
R		 51
0.8		 55
0.9		 61
0.6		 67
0.4		 75
0.1		 85
0.1		 87
1.0		 89
0.9		 83
0.7		 71
0.4		 60
0.6		 52
0.9
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Hythergraphs

graph for Aukland
Figure 1. Climatograph for Aukland, N. Z. Simple graphs can be constructed for an analysis of climate and weather data. The method was originated in 1910 and first applied to a practical problem in 1916. In constructing the graph, two related variables are plotted on the graph paper. The vertical scale represents temperature and the horizontal scale represents moisture (humidity or rainfall). The monthly mean values are plotted as a series of points, one for each month and the respective points are joined by a line in order of the months. The polygon thus obtained is termed a hythergraph if temperature and rainfall are used, or a climatograph if temperature and relative humidity are correlated. “Climograph” is a corruption of the latter term, and has been used to mean both climatograph and hythergraph. The time unit used may be any period (hour, week, day) but is usually month or week.

For example, for Aukland, the climatograph would look like Figure 1.


Problem:

Plot hythergraphs for Barrow, Boston, Cuyaba, Delhi, and Phoenix. Hythergraphs for Boston, Barrow, Cuyaba, and Delhi could probably be put on the same graph with different symbols, while at least Delhi and Phoenix will have to go on separate graphs because of overlapping data points. Perhaps Barrow, Boston, and Delhi could go on one graph and Cuyaba and Phoenix on another. Suggested scales are –20 to 100° F for temperature and 0 to 10 inches for precipitation. As time and interest allow, hythergraphs for the other cities could also be constructed.

Show Me the graph for
| Athens | Aukland | Barrow | Boston | Cincinnati | Cuyaba |
| Delhi | Georgetown | Monterrey | Moscow | Odessa | Phoenix |


Hythergraphs, Continued

Hythergraphs also furnish a convenient means of comparing one season with another. They are convenient and useful for giving a comparison of the climate in a series of localities or to determine the probability limits for the distribution of a particular species of organism. For, example, a composite climatograph can be constructed for a locality or year in which there were large numbers of a given species of insect and compared to a climatograph for another locality or year in which no or few of that species occurred. The index thus obtained is valuable in an analysis of the influence of climatic variations upon the population size of that species.

The data in Table 2 give mean temperature and monthly total precipitation for two different years in an area of southern Illinois. The first year was particularly favorable for a species of moth called the codling moth (a fruit pest) and there were large numbers of these moths in that year. The second year, there were few moths and they were not a problem.

Table 2. Monthly Temperature and Total Precipitation
for Two Years in a Southern Illinois Codling Moth Area
  Moths Abundant Moths Scarce
Month  (no.)   Temp. (° F)   Ppt. (inches)   Temp. (° F)   Ppt. (inches) 
Jan 1 35.5 0.8 36.0 1.7
Feb 2 26.0 2.7 28.0 1.7
Mar 3 40.0 1.8 42.0 4.9
Apr 4 53.0 3.1 53.5 5.3
 May — 1st half  5A 59.0 2.6 N/A N/A
 May — 2nd half  5B 68.0 1.6 63.5 5.1
Jun 6 77.5 1.4 73.5 3.6
Jul 7 81.5 2.3 78.0 3.6
Aug 8 74.5 3.3 74.0 5.7
Sep 9 68.0 3.7 68.0 1.2
Oct 10 57.5 5.3 57.0 1.7
Nov 11 46.5 4.2 43.0 1.8
Dec 12 35.5 0.8 36.0 1.7


Problem:

Draw hythergraphs from the data in Table 2 (can be on same graph). Based on the hythergraphs:

Show Me the graph for
| Moths Abundant | Moths Scarce |

  1. How does the precipitation for the period of September through November compare for the two years? Make a similar comparison for the period from March through July.
    Show Me!
  2. How do the temperatures for the period of May through July compare for the two years?
    Show Me!
  3. Do you think any of these differences are significant (in terms of the moth population)?
    Show Me!

Copyright © 1998 by J. Stein Carter. All rights reserved.
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