Climate and Weather

Weather and Climate

Few factors affect a traveler's experience as simply yet profoundly as the weather. To a large extent, the location and climate of a destination determine the weather conditions a traveler can expect.

The earth has five major climate zones, referred to as the humid tropical, dry, subtropical, continental, and polar climates. Each of these principal zones is subdivided into more specific subzones, based on the prevailing vegetation. For example, the tropical climates are divided into the rain forest, monsoon, savanna, and rare dry zones.

Humid tropical climates are characterized by hot, wet climates, with average temperatures of 64 degrees F (18 degrees C) or higher and an average rainfall of 80 inches (203 centimeters) or more. Such a climate promotes the growth of lush vegetation. The dense tropical rain forests that thrive in the tropical zones produce through photosynthesis nearly one third of the oxygen in the earth's atmosphere. The largest tropical rain forest is found along the Amazon River that stretches in a meandering, north-south direction across almost the entire width of the northern part of South America. Other tropical rain forests grow in parts of Africa, Asia, Central America, and the Caribbean.

Not all tropical regions receive year-round rainfall. Areas farther from the equator but still within the tropical latitudes have long dry periods, which prevent the growth of rain forests. In these areas, called the tropical savanna zone, the terrain is typified by scattered trees and coarse grass, which change with the seasons from lush green to dry brown. Tropical savannas are found primarily in Africa and South America.

Dry climates include the steppe, low-latitude steppe, mid-latitude steppe, desert, low-latitude desert, and mid-latitude desert zones. The desert zones comprise areas that have little or no vegetation, whereas the steppe zones consist of wetter areas that support grass and shrubs, but few trees.

A vast steppe stretches across the midsection of the Eurasian landmass from Kazakhstan to Mongolia. Other major portions of the steppe zone are found in the western United States, northern Mexico, and Central and Southern Africa. In all, desert comprises one fifth of the earth's landmass. The largest is the Sahara Desert, which occupies a third of the entire African continent. Nearly three fourths of the surface of Australia lies in the desert zone. Other principal deserts are found in northern China, Pakistan, the southwestern United States, and Northern Mexico.

Subtropical climates are found primarily in mid-latitude areas with mild winters. Broad-leafed forests are the principal form of vegetation in this climate zone, where the average temperature of the coldest month is between 27 degrees F and 64 degrees F. A subtropical climate is found in of Italy and other Mediterranean countries and in coastal areas near San Francisco, California; Santiago, Chile; and Portugal. Much of the eastern United States, Great Britain, New Zealand, and the western coast of Alaska are also classified in this climate zone, as are areas of evergreen forest in mountainous humid tropical climates.

Continental climates are those where forests are the primary vegetation, the average temperature of the warmest month is more than 50 degrees F, and the average temperature of the coolest month is 27 degrees F. In the humid, warm summer zones, some rainfall occurs year-round, but the wettest month occurs in summer. The northern Great Plains of the United States, the northern part of the Yellow Sea, much of the area between Manchuria and the Sea of Okhotsk, a large portion of Siberia, and a large area stretching from eatern Europe into Asia all are part of the continental climates zone.

Polar climates include the tundra and ice cap zones. Vast areas of North America, Europe, and Asia lie in the tundra zone, where the average temperature of the warmest month is less than 50 degrees F but more than 32 degrees F. In the ice cap zone, which includes the North and South Poles and the interior of Greenland, the average temperature of the warmest month is 32 degrees F or less.