Life in the Tucson Desert

Deserts are areas of extreme heat  and dryness, just as most of us envision them. More scientifically, deserts, also called arrid regions, characteristically receive less than 10 inches of precipitation a year. In some deserts, the amount of evaporation is greater than the amount of rainfall. Semiarid regions average 10 to 20 inches of annnual precipitation. Typically, desert moisture occurs in brief intervals and is unpredictable from  year to year.  About one-third of the earth's land mass is arid to semiarid (either desert or semidesert).

Evaporation is also an  important factors contributing to aridity.  In some deserts, the amount of water evaporating, exceeds the amount of rainfall. Rising air cools and can hold less moisture, producing clouds and precipitation; falling air warms, absorbing moisture.  Areas with few clouds, bodies of water and little to no vegetation absorb most of the sun's radiation, thus heating the air at the soil surface. More humid areas deflect heat in clouds, water and vegetation remaining cooler. High wind in open country also contributes to evaporation.

Locations of deserts have changed throughout geologic time as the result of continental drift and the uplifting of mountain ranges. Modern desert regions are centered in the horse latitudes, typically straddling theTropic of Cancer and theTropic of Capricorn, between 15 and 30 degrees north and south of the equator. Some deserts, such as the Kalahari in central Africa, are geologically ancient. The Sahara Desert in northern Africa is 65 million years old, while the Sonoran Desert of North America reached its northern limits only within the last 10,000 years.  Because they are poised in such harsh extremes of heat and aridity, deserts are among the most fragile ecosystems on the planet.

Need more information on our weather? E-mail me at: tucsontootsie@gci-net.com