Page 715 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

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The Köppen Climate Classification System
The Köppen climate classification system was designed by Wladimir Köppen (1846–1940), a German climatologist and botanist, and is widely used for its ease of comprehen- sion. The basis of any empirical classification system is the choice of criteria used to draw lines on a map to desig- nate different climates. The Köppen–Geiger climate clas- sification uses average monthly temperatures, average monthly precipitation, and total annual precipitation to devise its spatial categories and boundaries. But we must remember that boundaries are transition zones of gradual change. The trends and overall patterns of boundary lines are more important than their precise placement, espe- cially with the small scales generally used on world maps.
Take a few minutes and examine the Köppen system, the criteria, and the considerations for each of the principal climate categories. The modified Köppen–Geiger system has its drawbacks, however. It does not consider winds, temper- ature extremes, precipitation intensity, quantity of sunshine, cloud cover, or net radiation. Yet the system is important because its correlations with the actual world are reasonable and the input data are standardized and readily available.
Köppen’s Climatic Designations
The genetic, or causative, factors that form the basis of Köppen’s climate categories are presented on a world cli- mate map in Figure 10.2. Here we present the actual criteria that Köppen developed. The Köppen system uses capital letters (A, B, C, D, E, H) to designate climatic categories from the equator to the poles. The guidelines for each of these categories are in the margin of Figure C.1.
Five of the climate classifications are based on ther- mal criteria:
A. Tropical (equatorial regions)
C. Mesothermal (Mediterranean, humid subtropical, marine west coast regions)
D. Microthermal (humid continental, subarctic regions)
E. Polar (polar regions)
H. Highland (compared to lowlands at the same lati- tude, highlands have lower temperatures—recall the normal lapse rate—and more efficient precipitation due to lower moisture demand)
Only one climate classification is based on moisture as well: B. Dry (deserts and semiarid steppes)
Within each climate classification additional lower- case letters are used to signify temperature and moisture conditions. For example, in a tropical rain forest Af climate, the A tells us that the average coolest month is above 18°C (average temperature for the month), and the f indicates that the weather is constantly wet, with the driest month receiving at least 6 cm of precipitation. (The designation f is from the German feucht, for “moist.”) As you can see on the climate map, the tropical rain forest Af climate domi- nates along the equator and equatorial rain forest.
In a Dfa climate, the D means that the average warm- est month is above 10°C, with at least one month falling below 0°C; the f says that at least 3 cm of precipitation falls during every month; and the a indicates a warmest summer month averaging above 22°C. Thus, a Dfa climate is a humid-continental, hot-summer climate in the micro- thermal category.
Köppen Guidelines
The Köppen guidelines and map portrayal are in Figure C.1. First, check the guidelines for a climate type, then the colour legend for the subdivisions of the type, then check out the distribution of that climate on the map. You may want to compare this with the climate map in Figure 10.2 that presents causal elements that produce these climates.
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