Investigating Earth's Desert, Grassland, and Rainforest Biomes
INVESTIGATING EARTH'S DESERT GRASSLAND AND RAINFOREST BIOMES and the temperature and amount of sunshine all play a role Some definitions of deserts focus on the imbalance between the amount of precipitation received and the amount of moisture that could be lost through evapo ration and through plants leaves In the Sonoran Desert in the southwestern United States and Mexico for example a year's potential evaporation the amount of evap oration that would occur if water were always present is some 100 inches 250 centime ters This is about 20 times the actual annual rainfall Rainfall in deserts is not only scanty but also erratic Most deserts have at least a few days of rain a year but some may get no rain at all for several years or receive a year's amount in one storm For example Iquique in northern Chile had no rain for four years The fifth year brought 0 6 inch 1 5 centime ters making a five year average of 0 12 inch 0 3 centimeter At another time 2 5 inches 6 4 centimeters fell in a single shower Temperatures range widely in deserts In hot deserts daytime air temperatures can regularly exceed 100°F 38° C in summer Al Aziziyah Libya holds the record for the hottest temperature with a high of 136° F 57 8° C while Death Valley Calif comes
THE DESERT ENVIRONMENT Rock strewn tundra of the barren Arctic lands of Polar Bear Pass on Bathurst Island Nunavut Can Regions around the poles are sometimes called cold deserts Brian Milne First Light
INVESTIGATING EARTH'S DESERT GRASSLAND AND RAINFOREST BIOMES close with 134°F 56 7° C Winters are cold in temperate deserts located far from the Equator The Gobi in Central Asia for example has an average low temperature of 40°F 40° C in January and an average high of 113° F 45° C in July The temperature drops sharply in the des ert night Dry air cloudless skies and bare dry earth furnish ideal conditions for the cooling of air after sunset A 24 hour range of 25 to 45° F 14 to 25° C is common and it may exceed 60 to 70°F 33 to 39° C WORLD DISTRIBUTION There are two main types of arid desert hot and temperate Most of the Earth's deserts are found between 20° and 35° in both north and south latitudes near the Tropic of Cancer and the Tropic of Capricorn respectively Except for a couple of coastal deserts kept cool by ocean currents these deserts are hot They occupy subtropical regions that straddle a wet tropical region around the Equator Because of the predominant air circulation patterns the air that descends into the subtropical regions has already rained out most of its moisture over the tropical lands The air is also heated as it descends which further prevents rain
THE DESERT ENVIRONMENT 80 Principal regions of hot deserts Principal regions of temperate deserts Most hot deserts lie between 20° and 35° north and south of the equator The main temperate deserts are found in the middle latitudes Temperate deserts are found farther from the Equator in the middle latitudes They occur mainly in Central Asia with smaller areas in western North America southeast ern South America and southern Australia These deserts are generally separated from the coast by mountains or by great distance Air picks up moisture from the ocean but by the time it reaches these regions it has lost much of its moisture over either the moun tains or the land nearer the coast
