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31-12-2008, 10:29 AM
What is a Desert Like¿
The desert is a land of extremes: extreme heat and extreme dryness; sudden flash floods and cold nights. Because deserts are such a harsh environment, deserts often have names likes "Death Valley," "the empty quarter," and "the place from where there is no return."
Dryness
Deserts are usually very, very dry. Even the wettest deserts get less than ten inches of precipitation a year.
In most places, rain falls steadily throughout the year. But in the desert, there may be only a few periods of rains per year with a lot of time between rains. When it does rain, there may be quite a downpour! After the rain, desert flowers bloom.
Hot During the Day, Cool at Night
Everyone knows that during the day many deserts are hot, very hot. Temperatures in excess of 100 degrees fahrenheit are not uncommon. Yet at night, the same deserts can have temperatures fall into the 40s or 50s? Why?
Other biomes are insulated by their humidity (water vapor in the air). Temperate deciduous forests, for example, may have 80 percent humidity or more during the day. This water reflects and absorbs sunlight and the energy it brings. At night the water acts like a blanket, trapping heat inside the forest.
Since deserts usually have only between 10 and 20 percent humidity to trap temperatures and have so few trees and other vegetation to retain heat, they cool down rapidly when the sun sets, and heat up quickly after the sun rises.
*Where Are Deserts Located?
&Types of Deserts
Believe it or not, deserts come in two varieties: hot and cold.
*Hot Deserts of the World
The four major North American deserts of this type are the Chihuahuan, Sonoran, Mojave and Great Basin. Others outside the U.S. include the Southern Asian realm, Neotropical (South and Central America), Ethiopian (Africa) and Australian.
The seasons are generally warm throughout the year and very hot in the summer. The winters usually bring little rainfall. Temperatures exhibit daily extremes because the atmosphere contains little humidity to block the Sun’s rays. Desert surfaces receive a little more than twice the solar radiation received by humid regions and lose almost twice as much heat at night. Many mean annual temperatures range from 20-25° C. The extreme maximum ranges from 43.5-49° C. Minimum temperatures sometimes drop to -18° C.
Rainfall is usually very low and/or concentrated in short bursts between long rainless periods. Evaporation rates regularly exceed rainfall rates. Sometimes rain starts falling and evaporates before reaching the ground. Rainfall is lowest on the Atacama Desert of Chile, where it averages less than 1.5 cm. Some years are even rainless. Inland Sahara also receives less than 1.5 cm a year. Rainfall in American deserts is higher—almost 28 cm a year.
*Cold Deserts of the World
These deserts are characterized by cold winters with snowfall and high overall rainfall throughout the winter and occasionally over the summer. They occur in the Antarctic, Greenland and the Nearctic realm. They have short, moist, and moderately warm summers with fairly long, cold winters. The mean winter temperature is between -2 to 4° C and the mean summer temperature is between 21-26° C.
The winters receive quite a bit of snow. The mean annual precipitation ranges from 15-26 cm. Annual precipitation has reached a maximum of 46 cm and a minimum of 9 cm. The heaviest rainfall of the spring is usually in April or May. In some areas, rainfall can be heavy in autumn. The soil is heavy, silty, and salty. It contains alluvial fans where soil is relatively porous and drainage is good so that most of the salt has been leached out.
The plants are widely scattered. In areas of shad-scale, about 10 percent of the ground is covered, but in some areas of sagebush it approaches 85 percent.
References:
1-http://www.ucmp.berkeley.edu/glossary/gloss5/biome/deserts.html
2-student book
Only remaining: -
The project is about the deserts. So this project talk many things like:-
-. What is a Desert Like?
- *Where Are Deserts Located?
- Hot Deserts of the World
- Cold Deserts of the World
Title Number of page
Introduction…………………………….2
What is a Desert Like?.................................3
*Where Are Deserts Located?...........................4
*Hot Deserts of the World………………4
*Cold Deserts of the World……………5
desert plant and desert animals…………6__7
Summary………...…………………….8
The desert is a land of extremes: extreme heat and extreme dryness; sudden flash floods and cold nights. Because deserts are such a harsh environment, deserts often have names likes "Death Valley," "the empty quarter," and "the place from where there is no return."
Dryness
Deserts are usually very, very dry. Even the wettest deserts get less than ten inches of precipitation a year.
In most places, rain falls steadily throughout the year. But in the desert, there may be only a few periods of rains per year with a lot of time between rains. When it does rain, there may be quite a downpour! After the rain, desert flowers bloom.
Hot During the Day, Cool at Night
Everyone knows that during the day many deserts are hot, very hot. Temperatures in excess of 100 degrees fahrenheit are not uncommon. Yet at night, the same deserts can have temperatures fall into the 40s or 50s? Why?
Other biomes are insulated by their humidity (water vapor in the air). Temperate deciduous forests, for example, may have 80 percent humidity or more during the day. This water reflects and absorbs sunlight and the energy it brings. At night the water acts like a blanket, trapping heat inside the forest.
Since deserts usually have only between 10 and 20 percent humidity to trap temperatures and have so few trees and other vegetation to retain heat, they cool down rapidly when the sun sets, and heat up quickly after the sun rises.
*Where Are Deserts Located?
&Types of Deserts
Believe it or not, deserts come in two varieties: hot and cold.
*Hot Deserts of the World
The four major North American deserts of this type are the Chihuahuan, Sonoran, Mojave and Great Basin. Others outside the U.S. include the Southern Asian realm, Neotropical (South and Central America), Ethiopian (Africa) and Australian.
The seasons are generally warm throughout the year and very hot in the summer. The winters usually bring little rainfall. Temperatures exhibit daily extremes because the atmosphere contains little humidity to block the Sun’s rays. Desert surfaces receive a little more than twice the solar radiation received by humid regions and lose almost twice as much heat at night. Many mean annual temperatures range from 20-25° C. The extreme maximum ranges from 43.5-49° C. Minimum temperatures sometimes drop to -18° C.
Rainfall is usually very low and/or concentrated in short bursts between long rainless periods. Evaporation rates regularly exceed rainfall rates. Sometimes rain starts falling and evaporates before reaching the ground. Rainfall is lowest on the Atacama Desert of Chile, where it averages less than 1.5 cm. Some years are even rainless. Inland Sahara also receives less than 1.5 cm a year. Rainfall in American deserts is higher—almost 28 cm a year.
*Cold Deserts of the World
These deserts are characterized by cold winters with snowfall and high overall rainfall throughout the winter and occasionally over the summer. They occur in the Antarctic, Greenland and the Nearctic realm. They have short, moist, and moderately warm summers with fairly long, cold winters. The mean winter temperature is between -2 to 4° C and the mean summer temperature is between 21-26° C.
The winters receive quite a bit of snow. The mean annual precipitation ranges from 15-26 cm. Annual precipitation has reached a maximum of 46 cm and a minimum of 9 cm. The heaviest rainfall of the spring is usually in April or May. In some areas, rainfall can be heavy in autumn. The soil is heavy, silty, and salty. It contains alluvial fans where soil is relatively porous and drainage is good so that most of the salt has been leached out.
The plants are widely scattered. In areas of shad-scale, about 10 percent of the ground is covered, but in some areas of sagebush it approaches 85 percent.
References:
1-http://www.ucmp.berkeley.edu/glossary/gloss5/biome/deserts.html
2-student book
Only remaining: -
The project is about the deserts. So this project talk many things like:-
-. What is a Desert Like?
- *Where Are Deserts Located?
- Hot Deserts of the World
- Cold Deserts of the World
Title Number of page
Introduction…………………………….2
What is a Desert Like?.................................3
*Where Are Deserts Located?...........................4
*Hot Deserts of the World………………4
*Cold Deserts of the World……………5
desert plant and desert animals…………6__7
Summary………...…………………….8