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Unit 16


Unit Overview

This unit discusses the spatial distribution of climate types. The main sections are:

  • Classifying climates
  • Köppen climate classification system
  • Regional distribution of climate types
  • Boundaries of climate regions

Climate is the synthesis of weather for a particular location as represented by the statistical collective of that location's atmospheric conditions during a specified interval of time (usually several decades). Many researchers have attempted to simplify the extreme heterogeneity of the Earth's climates by devising climate classification schemes, whereby distinct boundaries are drawn for specific climate types. Therefore, each location on Earth fits into a specific, pre-defined climate type.

Climate classifications are based typically on temperature and precipitation characteristics. The Köppen climate classification system is widely used; the boundaries of the classes correspond to boundaries of general vegetation types (e.g., boreal forests). This classification system implies dramatic changes from one climate type to another. Across the globe, climate varies gradually.

Unit Objectives

  • To define climate and discuss the general problems of climate classification based on dynamic phenomena
  • To outline a useful climate classification scheme devised by Köppen and extended by Geiger, based on temperature and precipitation amounts and timing
  • To apply the modified Köppen classification system to the Earth, and briefly describe appropriate climate regions as they appear on a hypothetical continent and the world map

Glossary of Key Terms

Climate The long-term conditions (over at least 30 years) of aggregate weather over a region, summarized by averages and measures of variability; a synthesis of the succession of weather events we have learned to expect at any given location.
Hypothetical continent The Earth's landmasses generalized into a single, idealized, shield-shaped continent of uniform low elevation.
Köppen climate calssification system A descriptive classification of the world's climates, based its association with plant life, devised by Wladimir P. Köppen.

Unit Outline

  • Classifying Climates
    • Climate is defined as the average values of weather components, such as temperature and precipitation, for at least a thirty-year period
  • Köppen climate classification system
    • Six major climate groups
      • tropical (A)
      • arid (B)
      • mesothermal (C)
      • microthermal (D)
      • polar (E)
      • highland (H)
    • Precipitation indicators: f, m, w, s
  • The regional distribution of climate types
    • Hypothetical continent of uniform elevation used as model
    • A climates near equator, extend about 25 degrees in either direction from it
      • tropical rainforest (At)
      • savanna (Aw)
      • monsoon (Am)
    • B climates are poleward of A climates and on west coasts of continents, associated with subsiding air of subtropical highs
      • desert (B W)
      • steppe (BS)
    • C climates are located in the middle latitudes and are mesothermal (moderate temps)
      • Mediterranean (Cs)
      • humid climates with moist winters (Ct)
      • subtropical monsoon (Cw)
    • D climates are cold, and are located in upper-middle and subpolar latitudes
      • precipitation throughout the year (Dt)
      • drier, harsher winters (Dw)
    • E climates are located poleward of the Arctic and Antarctic Circles (66 ~ degrees)
      • tundra (ET)
      • ice cap or frost (EF)
    • H (highland) climates are found in the upper regions of mountainous areas, too cold to support vegetation
  • Boundaries of climate regions
    • Köppen system does not really consider causes of climate and some links to vegetation are not very strong
    • Köppen system best for global or regional, large-scale patterns
    • At the micro-level, climate boundaries are constantly changing

Review Questions

  1. Compare and contrast the B and C climate classifications. List the major subclasses of each, and the type of vegetation associated with them.
  2. Why can highland (H) climates not support vegetation?
  3. Describe generally the pattern of climate types across a hypothetical continent of uniform low elevation, using Fig 16.2 as a guide.