The 12 Climate Regions
Tropical wet climates
Tropical wet climates are hot and muggy the year around. They support dense
tropical rain forests. Rainfall is heavy and occurs in frequent showers and
thunderstorms throughout the year. Average annual rainfall varies from about 70
to 100 inches (175 to 250 centimeters). Temperatures are high, and they change
little during the year. The coolest month has an average temperature no lower
than 64 degrees F (18 degrees C). The temperature difference between day and
night is greater than the temperature difference between summer and winter.
Frost and freezing temperatures do not occur. Plants grow all year.
Tropical wet and dry climates occur in areas next to
regions that have tropical wet climates. Temperatures in tropical wet and dry
climates are similar to those in tropical wet climates, where they remain high
throughout the year. The main difference between the two climates lies in their
rainfall. In tropical wet and dry climates, winters are dry, and summers are
wet. Generally, the length of the rainy season and the average rainfall decrease
with increasing latitude. Not enough rain falls in tropical wet and dry climates
to support rain forests. Instead, they support savannas--grasslands with
scattered trees.
Semiarid and desert (arid) climates
Semiarid and desert climates occur in regions with little precipitation. Desert
climates are drier than semiarid climates. Semiarid climates, also called steppe
climates, usually border desert climates. In both climate groups, the
temperature change between day and night is considerable. One reason for the
wide swings in temperature is that the the skies are clear and the air is dry.
Clouds would reflect much of the sun's intense radiation during the day, slowing
the rate of heating of the air near the surface. At night, clouds and water
vapor would absorb much of the earth's radiation--most of which consists of
infrared rays--slowing the rate of cooling.
Semiarid and desert climates occur over a greater land area
than any other climate grouping. They occur in both tropical and middle
latitudes. They cover broad east-west bands near 30 degrees north and south
latitude.
Middle latitude semiarid and desert climates are in the rain shadows of mountain
ranges. Winds that descend the leeward slopes of these ranges are warm and dry.
Middle latitude semiarid areas and deserts differ from their tropical
counterparts mainly in their seasonal temperature changes. Winters are much
colder in middle latitude semiarid areas and deserts.
Subtropical dry summer climates (Mediterranean)
Subtropical dry summer climates feature warm to hot, dry summers and mild, rainy
winters. These climates, sometimes called Mediterranean climates, occur on the
west side of continents roughly between 30 degrees and 45 degrees latitude. The
closer to the coast the area is, the more moderate the temperatures and the less
the contrast between summer and winter temperatures.
Humid subtropical climates
Humid subtropical climates are characterized by warm to hot summers and cool
winters. Rainfall is distributed fairly evenly throughout the year. Winter
rainfall--and sometimes snowfall--is associated with large storm systems that
the westerlies steer from west to east. Most summer rainfall occurs during
thunderstorms and an occasional tropical storm or hurricane. Humid subtropical
climates lie on the southeast side of continents, roughly between 25 degrees and
40 degrees latitude.
Humid oceanic climates (Marine West Coast)
Humid oceanic climates are found only on the western sides of continents where
prevailing winds blow from sea to land. The moderating influence of the ocean
reduces the seasonal temperature contrast so that winters are cool to mild and
summers are warm. Moderate precipitation occurs throughout the year. Low clouds,
fog, and drizzle are common. Thunderstorms, cold waves, heat waves, and droughts
are rare.
Humid continental climates Humid continental climates
feature mild to warm summers and cold winters. The temperature difference
between the warmest and coldest months of the year in-creases inland. The
difference is as great as 45 to 63 Fahrenheit degrees (25 to 35 Celsius
degrees). Precipitation is distributed fairly evenly throughout the year, though
many locations well inland have more precipitation in the summer.
Snow is a major element in humid continental climates. Winter temperatures are
so low that snowfall can be substantial and snow cover persistent. Snow cover
has a chilling effect on climate. Snow strongly reflects solar radiation back
into space, lowering daytime temperatures. Snow also efficiently sends out
infrared radiation, lowering nighttime temperatures.
Subarctic climates
Subarctic climates have short, cool summers and long, bitterly cold winters.
Freezes can occur even in midsummer. Most precipitation falls in the summer.
Snow comes early in the fall and lasts on the ground into early summer.
Subarctic climates
Tundra climates are dry, with a brief, chilly summer and a bitterly cold winter.
Continuous permafrost (permanently frozen ground) lies under much of the
treeless tundra regions.
Icecap climates
Icecap climates are the coldest on earth. Summer temperatures rarely rise above
the freezing point. Temperatures are extremely low during the long, dark winter.
Precipitation is meager and is almost always in the form of snow.
Highland climates
Highland climates occur in mountainous regions. A highland climate zone is
composed of several areas whose climates are like those found in flat terrain.
Because air temperature decreases with increasing elevation in the mountains,
each climate area is restricted to a certain range of altitude.
A mountain climber may encounter the same sequence of climates in several
thousand meters of elevation as he or she would encounter traveling northward
several thousand kilometers. For example, the climate at the base of a mountain
might be humid subtropical, and the climate at the summit might be tundra.