 Climate is average of weather conditions for
30+ years
 Climatologists employ many
different tools to organize the
wealth of information about
earth's climates to bring order
and understanding
 graphs, classification
systems, and maps are
among the most common
 Temperature & Precipitation
are the most important
expressions of climate,
and these have been used in Climographs (See above)
and in climate classification schemes
Climate Classification Systems
There are two fundamental types of classification
used in modern climatology:
1. Genetic classification, based on the causes or
genesis of climatic variation
• Requires information about many climatic
elements – solar radiation, air masses, fronts,
pressure systems, etc. (e.g., A.N. Strahler’s
Classification based on Air Mass origin and interactions
→ 3 major groups + H: Low-, Mid- and High-latitude
Climates + Undifferentiated Highlands); each group
subdivided into climates with unique characteristics.
• Complex and difficult to create and use
because of the multitude of variables and data
needed → Not widely used.
2. Empirical Classification that are based on observable
characteristics and/or statistical and mathematical parameters
Most climate
classification
systems,
including the
Early Greek
System
(Torrid,
Temperate,
Frigid),
and the
Thornthwaite
System, are
examples of
empirical
classification
Thornthwaite classification system focuses on a local scale & is based
on the concept of potential evapotranspiration  Climate types based on
water requirements.
• Motivated by the desire to predict the supply and demand for water in
different climate regions  Moisture Index
• Recognizes 5 global climatic zones based on potential ET (See Map below)
• However, the most widely used climate classification was
developed by the German botanist and climatologist
Wladimir Koppen
The Koppen Climate Classification:
An empirical system
• Easy to use, and data requirements are minimal
• Based on observations of temperature and precipitation
These are two basic climatic characteristics that can
be readily measured, and probably the ones with the
longest historical record
• Each climate is defined according to set values of mean
monthly precipitation & mean monthly temperature,
the grouping based on annual averages and seasonal
extremes
• Climate regions formulated to coincide with well-defined
vegetation regions, and described by the natural
vegetation most often found there
• The Simplified Köppen system, as modified by later
climatologists, recognizes six major climatic types,
each designated by a capital letter:
 A = Tropical Rainy Climates
 B = Arid (Dry) Climates
 C = Humid Mesothermal (Mild Winter) Climates
 D = Humid Microthermal (Severe Winter) Climates
 E = Polar Climates
 H = Highland Climates
• The subtypes of the major categories are distinguished by a
second (Upper or lower case) letter, and often a third
(lower case) letter, giving us 14 to 23 sub-categories.
Modified Koppen Classification of World Climates
Note:
•(B) Arid (Dry) Climates
Evaporation (Potential ET) exceeds precipitation
BWh, BWk: Desert (Precipitation less than half the potential ET)
BSh, BSk: Steppe (Precipitation more than half the potential ET)
Highland Climates  Topoclimates
 Vertical Zones of Microclimates and Vegetation
Urban heat island effect – cities often hotter
than surrounding countryside
 Stone, concrete, and asphalt re-emit lots of
solar energy
 Little surface water to transfer heat
 Thermal contribution from combustion
 Buildings block winds
 Air pollution absorbs heat to produce local
greenhouse warming
The urban heat island effect
Warm air rising over a city
creates a low-pressure zone.
As a result, precipitation is
greater in the city than over
the surrounding countryside.
Factors Influencing the World Climatic Regions
Climate patterns show the close relationships among the elements and factors of
weather and climate:
1) Latitude and its influence on solar radiation received
2) Air mass influences
3) Location of global high and low pressure zones/belts
4) Pattern of prevailing winds (wind belts)
5) Location of mountain barriers
6) Heat exchange from ocean currents
7) Distribution of land and water
8) Altitude or elevation
9) Human Activities – Destruction of forests, creation of reservoirs, urbanization
– Urban Heat Islands
At a macro level, the first three factors are most important in influencing a region's climate.
Diversity of Climates within Proximate Areas – Influence of Geography?

Vegetation is the most visible expression of climate
Classification of Global Natural Vegetation
 HOW DOES CLIMATE INFLUENCE OTHER ASPECTS
OF THE ENVIRONMENT?
• Animal life adapts to both climate and vegetation
• Soils develop in response to climate and vegetation
• Landforms are constantly modified by climate-related processes
• Water availability is related to humid vs. arid climates
 HOW DOES CLIMATE RELATE TO ECOSYSTEMS?
• The interaction of climate, vegetation, animal life, soils, and
landforms creates an environmental complex or ecosystem
• Unique ecosystems evolve primarily as a result of differing climate
conditions
 WHAT IS THE IMPACT OF CLIMATE UPON PEOPLE'S LIVES?
• Regions of extreme climatic conditions have fewer people
-- Deserts, rainforests, polar regions
• Climate influences agriculture
-- Choice of crops grown and animals raised
• Tourism and recreation patterns are shaped by climatic conditions
• Water resources availability and utilization also affected by climate
• Climate and disease – relationships have persisted despite
technological advancement
 Climatologists and geographers study and compare
climate regions that have evolved in response to
different moisture and temperature conditions, in
order to enhance our understanding of these and
other relationships.