Investigating Earth's Desert, Grassland, and Rainforest Biomes
CHAPTER 1 THE DESERT ENVIRONMENT A biome is a large region of Earth that has a certain climate and certain types of living things Occupying some 20 percent of the Earth's surface des erts are one of the planet's major types of biomes Any barren region that supports very little life may be called a desert More com monly however the term desert is reserved for regions that are barren because they are arid or dry Arid deserts receive little precipitation and are characterized by specialized plants that tolerate drought conditions and salty soils Deserts may or may not be hot Land features range from windswept expanses of loose sand to rugged mountains bare rock and plateaus strewn with gravel and boulders CLIMATE Deserts are areas in which there is a shortage of moisture available for plants There is no precise measure of how dry such an area must be to be called a desert Characteristically
THE DESERT ENVIRONMENT deserts receive an average of less than 10 inches 25 centimeters of rain or other pre cipitation per year Many deserts get less than half that amount of rain yearly and some receive almost none Regions with an average annual precipitation between some io and 16 inches 25 and 40 centimeters are often called semideserts But rainfall is not the only factor that influences how much water is available to sup port plants The distribution of the rainfall throughout the year the humidity of the air Desert rainfall is sparse and sporadic so some species of cactus lack leaves which means there is less surface area from which they can lose water iStockphoto Thinkstock
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
