Biomes of the World

Deserts

Deserts: Quick Facts

• A desert is a region of the earth that receives less than 25 centimeters of rainfall annually.

• Thirty percent of the earth’s surface is covered by desert.

• Most of the world’s deserts lie somewhere between the 20˚ and 30˚ lines of latitude on the western side of the continents

Desert Conditions

Deserts occur where evaporation of rainwater is greater than the volume of rain in that area.

Hot Days and Cold Nights

• Because there is generally no cloud cover in a desert, heat is lost through evaporation.

• The lack of moisture in the air, combined with the lack of vegetation allows the surface of the desert to release heat quickly once the sun has set.

West Coast Deserts

• Deserts generally occur in these areas because of climatic conditions.

• Hot, dry air is blown westward across the desert, causing the average temperature to increase.

West Coast Deserts

• Cold ocean currents from the west coast meet with the warm westward winds.

• Because evaporation from cold water is generally low, the amount of moisture in the air is limited, meaning less rain.

North America Deserts

• American deserts are different from most deserts because they exist separate from others, surrounded usually by mountain ranges.

• Also, the well-known symbol of deserts, cacti, are found only in North American deserts.

Common Desert Plants

• North America• cacti and small brush

• southern Africa • aloe plant

• northern Africa and the Middle East • date palm

Desertification

This is the process of semi-arid areas (areas with little annual rainfall) on the edges of deserts

becoming drier and changing into full deserts

Why Does Desertification Occur?

• Some believe that desertification is a natural process resulting from the climate changed causing lower rainfall and a shorter wet season.

• Those that believe desertification is caused by mankind point to pressure from overpopulated areas and the overuse of land to explain their theory.

Total Land Affected Worldwide

Worldwide over 8.1 million square kilometers (roughly the size of Brazil) has been affected by

desertification.

Slowing the Process

• The best way to slow desertification would be to dramatically reduce overgrazing, deforestation, and excessive cultivation of the land.

• As well, reforestation programs will help to bind the water to hold in soil.