Chapter 15 Notes. World Climates. Ancient Greek Climate Classification. Climate Classification
One of the first attempts at climate classification was made by the ancient Greeks, who divided each hemisphere into three zones: torrid, temperate and frigid. The basis of this classification scheme was Earth-Sun relationships.
There are many different climate classification schemes available today. A scheme is used based on the intended use of the classification system.
One of the most widely used systems is the Köppen classification system which is based on the distribution of natural vegetation.
The Köppen classification recognizes five principal climate groups, each designated by a capital letter:
Each of the five groups is further subdivided using specific criteria and symbols.
The tropical wet and dry is a transitional climatic region between the wet tropic and the subtropical deserts.
Temperature data show only modest differences between the wet tropics and the tropical wet and dry. Because of the somewhat higher latitude of most Aw stations, annual mean temperatures are slightly lower, and the annual temperature range is a bit greater.
This climate receive between 100 to 150 centimeters of precipitation per year, but the defining characteristic is the seasonal nature of the rainfall. Wet summers are followed by dry winters.
The Dry Climates (BWh, BSh, BWk, BSk)
A dry climate is define as a climate in which the yearly precipitation is less than the potential evaporation. The classification uses formulas that involve three variables: (1) average annual precipitation, (2) average annual temperature, and (3) seasonal distribution of precipitation
Dry regions of the world cover about 30% of Earth’s land area.
The two climates defined by a general water deficiency are (1) arid or desert, and (2) semiarid or steppe. Semiarid climates are a marginal and more humid variant of arid climates, and are transitional zones between deserts and the bordering humid climates.
Humid Continental Climates with Severe Winters (Dfa, Dfc, Dfd)
Located only in the Northern Hemisphere, between the latitudes of 40O and 50O. Average temperature of the coldest month is -3OC or below, and the average temperature of the warmest month exceeds 10OC.
Precipitation is generally greater in the summer and generally decreases toward the continental interior and from south to north. Wintertime precipitation is chiefly associated with the passage of fronts connected with traveling middle-latitude cyclones.
Subarctic climates, also called taiga climates, are situated north of the humid continental climates and south of the polar climates. The characterizing feature of these climates is the dominance of winter, although the summers, while short, are remarkably warm.
Polar climates are those in which the mean temperature of the warmest month is below 10OC. Annual temperature ranges are extreme, with the lowest annual means on the planet.
Although classifies as humid, precipitation in the polar climates is sparse, around 25-cm per year.
Two types of polar climates are recognized: (1) the tundra climate, characterized by permanently frozen subsoil called permafrost; and, (2) the ice-cap climate, which does not have a single monthly mean above 0OC.
Permafrost in the Northern Hemisphere
These climates are characterized by a great diversity of climatic conditions over a small area. Areas include the Rockies, Sierra Nevada, Cascades, and the mountains and plateaus of Mexico in North America.
The best known climatic effect of increased altitude is lower temperatures, but greater precipitation due to orographic lifting is also common.
Because atmospheric conditions fluctuate with altitude and exposure to the sun’s rays, a nearly limitless variety of local climates occur in mountainous regions.