In our part of the world, the average high temperature peaks in July, approaching 80 degrees. Sure, we’ll pay for this delightful summer six months from now, but it’s paradise compared to the height of summer elsewhere.
In California’s Death Valley, the average daily high and low temperatures are 115 and 87. No other North American location comes close to the persistent heat of this desert region. On July 10, 1913, the hottest temperature ever recorded in the Western Hemisphere was in Death Valley—134 degrees.
But what’s a story without a little controversy? Temperature records have been gathered for Death Valley since 1911, at the Greenland Ranch near the very appropriately named Furnace Creek. The 1913 reading is debatable because there was no documentation of the thermometer’s accuracy or the condition of its shelter. Also, there was a sandstorm at the time, leading to speculation that hot dust, blown into the thermometer by high winds, drove up the temperature, which has surpassed any and all subsequent temperature readings in Death Valley. A high of 129 was recorded there twice, in July 1960 and in July 1998.
The hottest temperature recorded in the Mojave Desert, south of Death Valley, was 130 degrees in 1887, but this is suspect for the same reasons. The summer of 1917 set records in the Mojave, with 43 consecutive days above 120 degrees, from July 6 to August 17. The longest stretch of triple-digit temps occurred there in 2001—154 days.
But deserts aren’t always hot. The Gobi Desert, which spans northwestern China and southern Mongolia, sees an annual rainfall of about eight inches in the east and less than three inches in the west. The name Gobi is Mongolian for “place without water.” July high temps in the Gobi reach over 110 degrees, with January lows as cold as -40.
And deserts aren’t always dry either. A “desert” is simply a barren region with very little precipitation. The largest deserts on Earth are the Antarctic and the Arctic. The northernmost part Siberia is also a polar desert and the coldest place in which humans live year-round.
The largest hot, dry desert—but technically only the third largest desert—is the Sahara in northern Africa. It covers 3.6 million square miles from the Atlantic Ocean to the Red Sea, and from the Mediterranean all the way down to the Niger River. Due to desertification, the Sahara is constantly growing. Since 1952, it has expanded 250,000 square miles. Fossil fuels and precious metals are abundant in the Sahara and their extraction has contributed to rapid desertification in recent decades.
Large swaths of the Sahara can go years between rainfall, and the mean annual temperature is 80 degrees. However, it’s not even among the top ten driest or windiest places on Earth. Oases comprise about 80,000 square miles of the Sahara, which combined with irrigation, make two percent of Saharan land fertile.
Deserts are classified as hot, cold, semi-arid, and/or coastal, depending on a combination of precipitation, temperature, and humidity. “Hot” deserts have greater evaporation than precipitation. “Cold” deserts may have high precipitation, but almost no humidity or vegetation.
Coastal deserts are mostly on the western side of continents, where cold water meets land and the air picks up little moisture, resulting in fog but low rainfall. Semi-arid deserts are often called steppes or tundra. They have grasses and shrubs, but are too dry and/or cold for trees.
About one-third of the land on Earth is desert, but the reasons for its moisture starvation vary. The Mojave Desert, for example, is a “rain-shadow desert,” which means it’s on the leeward side of a mountain range—in the Mojave’s case, the Sierra Nevada. Warm, moist air is drawn up the windward side of the mountains, where it precipitates before crossing over. The Gobi, too, is a rain-shadow desert, where the Himalayas block moist air masses moving north from the Indian Ocean.
The Equator forms deserts on the eastern side of persistent high-pressure areas. Warm, moist air at the Equator moves upwards. As it cools, it releases precipitation. This is why there are tropics near the Equator, but no deserts. As the air reaches the 30th to 38th parallel, it descends and warms, but is now dry. High-pressure-area deserts include the Kalahari and Namib in Africa, the Atacama in South America, and the Great Sandy in Western Australia. In the Northern Hemisphere, we have the Sahara and the Arabian and Syrian Deserts in the Middle East.
Death Valley is one example of an “endorheic basin,” a low-lying area with no water drainage, resulting in high salinity. Some, like Crater Lake in Oregon, still contain water, but most are arid, resulting in alkali flats, or “playas.” The Bonneville Salt Flats in Utah and the Black Rock Desert in Nevada are endorheic basins.
An unsolved mystery of playas is “sailing stones.” Rocks as large as 700 pounds slide across the basin, leaving trails an inch deep and 300 or more feet long, despite seemingly no force to propel them. One theory is that water freezes just below the playa surface, forming a sheet of barely submerged ice on which the rocks glide.
But enough of this hot talk! Look for a slightly warmer, slightly drier August, with a period of thunderstorms followed by a cool-down mid-month.