You'll also find additional ways to explore the deserts with recommended books videos and Web sites A listing of places to visit and a calendar of yearly events will continue the desert fun Most of all kids will discover a new frontier that they'll want to con tinue to explore So turn the page and start getting wild about
DISCOVERING DESERTS Close your eyes and imagine yourself in a desert In the desert of your imagination you might find yourself under the sun and standing on hot sand You might look up to see sand and rocks in all directions At night the sand becomes colder and the cloudless sky becomes full of stars Well that is what you will find in many deserts but not in all of them About one fifth of the surface of the earth is desert Most deserts are just as you imagine hot but others are very cold However all deserts have one thing in com mon very little rain The Biologist's View of the Desert There are many ways to define a desert Meteorolo gists define the desert by the amount of rainfall or precipitation it receives each year By definition a desert is a place that receives very little rain In fact the rain must be less than 19 7 inches 50 cm each year Look at a yardstick and see if you can find the 50 centimeter mark on the metric side You'll see that it's an extremely small amount of rain for one
whole year Compare that to the total amount of pre cipitation for the Albany New York area in 2002 at 40 8 inches 103 6 cm and you ll see that the desert receives a much smaller amount in one year What is the annual precipitation in your town Biologists look at rainfall when they define a desert but in addi tion they look at the evaporation rate Evaporation is when a liquid changes into a gas in this case the liq uid is the rain The evaporation rate describes the time it takes for the rain to dissipate into the air The evaporation rate must be greater than the amount of rainfall for the region to be called a desert by biolo gists Basically biologists focus on the little amount of rain deserts receive each year and the fact that most of that rain evaporates and is not beneficial to the animals and plants that live in the region What Makes Most Deserts So Hot Why are most deserts so hot Most deserts fall between the latitudes called the Tropic of Cancer and the Tropic of Capricorn If you look on a globe these latitude lines are found on either side of the equator This region is known as a subtropical climate belt Gen erally it has dry air and clear skies The winds are very dry because they have lost most of their mois ture in the more northern or southern regions These deserts are often described as hot dry deserts The winds along their western coasts are often cooled by cold ocean currents which cause them to drop only
small amount of water These areas are called coastal deserts Atacama in Chile is an example of a coastal desert Some deserts are found far inland or between mountains Often these are known as semiarid deserts Semiarid deserts are found in Utah Mon tana Russia and northern Asia The winds that reach these deserts have usually released most of their moisture before reaching the desert areas Desert regions also absorb more heat than humid regions Since there is not much to deflect the sun's rays bounce the rays off of the ground in the desert the desert absorbs 90 percent of the sun's rays or solar radiation which heats the ground and the layer of air above the ground In more humid regions of the world the sun's rays are deflected by clouds dust and water Ghost Rains In order for rain to fall there must be clouds in the sky Clouds rarely float over the desert but once in a while a cloud does float over the desert and rain falls to the hot ground below Sometimes the ground is so hot that there is a layer of hot air just above the ground This air can be so hot that it evaporates the rain as soon as the rain hits it The rain never reaches the dry earth of the desert When this occurs it is called a ghost rain Sometimes a ghost rain cools the layer of hot air enough so that if a second rainfall
