Characterized by extended periods of drought and extremes of heat and cold, deserts experience environmental conditions that are dangerous to desert life, including humans. Newcomers to desert areas need education about the hazards they may encounter, and these hazards vary according to the location and geology of the particular desert.
Deserts cover about one-fifth of Earth's land surface and there four major types: hot and dry, coastal, semiarid and cold. Examples of hot, dry deserts are the Sonoran Desert in the U.S., Australia's great central desert, the African Sahara and South America's Atacama Desert. Extreme summer maximum temperatures can reach 43.5 to 49 degrees Celsius (110 to 129 degrees Fahrenheit). Cold deserts exist in the Arctic, Antarctic and Greenland and have snow cover for most of the year. Rainfall in the Sahara and Atacama average less than 1.5 cm (0.6 inches), and American deserts average 28 cm (11 inches) yearly. Rainfall can be torrential when it occurs, causing dangerous flash floods and erosion. Strong winds carry sand and dry desert soils, creating damaging dust storms or haboobs.
Site-specific geological features present environmental hazards as well. In Arizona, groundwater withdrawal can lead to earth fissures over a mile long, up to 15 feet wide and hundreds of feet deep. Problem soils that expand and contract when wet or dry cause damage to homes and other structures. Arizona and Egypt share hazardous conditions because of underlying karst formations, or water-soluble rocks that develop caves, depressions, fractures and sinkholes, giving rise to unstable conditions. Earthquakes and volcanism are other hazards that can occur in deserts of the world.
Landslides happen when slopes are weakened by rainfall, earthquakes or wildfires. Fast-moving landslides, such as rock falls and avalanches, carry away houses and cover roads. In Saudi Arabia, landslides are considered more devastating than all other natural hazards combined. Areas of sand dunes are constantly on the move, shifted about by winds. In Egypt, sand dune migration is one of the most serious economical and environmental problems. After rainstorms, debris flows result from runoff waters moving and redepositing soil, plant material, rocks and boulders, and typically are 80 percent solids and 20 percent water. In Arizona, they occur primarily during summer monsoons.
Plants and animals with toxic components also present dangers to humans in deserts. Euphorbias that grow in African deserts have caustic, milky sap that can cause temporary or permanent blindness. Cacti native to North and South American deserts have fierce spines that cause painful punctures and lacerations. Venomous creatures such as snakes, scorpions, spiders and lizards inhabit deserts, and their bite or sting can cause human illness or death. In Africa, hordes of desert locusts destroy vast areas of natural vegetation and croplands. In the American Southwest, a pathogenic, soil-borne fungus causes the disease called valley fever or coccidioidomycosis, which can be fatal. Tiny, biting sand flies occur during rainy seasons in both Old World and New World deserts. They carry a serious disease called leishmaniasis, which is a significant health threat to U.S. military personnel deployed to areas such as the Middle East, Afghanistan and Africa.