What is a desert? That is not as simple as I thought. Deserts are defined by water—or rather, by the absence of water. Dryness and sunlight are what deserts are all about. Buckets of sunlight, rather than buckets of rain. Plants or animals that don’t like that cannot survive here. Some plants, amazingly, even prefer the south facing side of the mountain.
Geographers define deserts as land where evaporation exceeds rainfall. I was surprised to learn that there is no specific amount of rainfall that serves as an agreed upon criteria as what is and what is not a desert. Deserts range from extremely arid regions to those that are ample for the support of life. Geographers classify rainfall into semi-deserts that are ones that have precipitation between 150 and 300 to 400 mm per year. So called “true deserts” are those that have rainfall below 150 mm per year and extreme deserts as those with rainfall below 70 mm per year.
Deserts occupy about 26% of the continental areas of the world. Deserts occur in 2 distinct belts. One is between 15º and 35º latitude in both the Northern and Southern hemispheres—the Tropic of Cancer and Tropic of Capricorn.
There are 14 deserts in the world (depending on who is counting) with an area larger than 52,000 sq. km (20,100 sq. mi.). It may surprise some that the largest desert in the world is not the Sahara desert. It is only the second largest. The largest is Antarctica not often thought of as a desert, but that is what it is. Antarctica has 14,000,000 sq. km. and the Sahara with 9,000.000 sq. km.
There are 5 distinct deserts in the American Southwest: the Sonoran, The Chihuahuan, The Great Basin, and the Mojave. Some also include the Colorado as a separate desert. Although each is a desert, each is also different.
The Sonoran Desert, where we have been living for the 4th year, is semi-arid desert and it covers part of southern California and Arizona as well as northern Mexico. Because of summer’s “monsoons” and winter storms this is the wettest of all the North American deserts. It is most well known for its iconic tall Saguaros cactus some of which can reach 50 feet in height.
The Great Basin is the most characteristic of the Southwest with its canyon, mesas, buttes, and cliffs.
The Mojave Desert is a large desert that spreads across northern Arizona, Nevada, and California. It is dry most of the year but a small amount of winter rain can bring it to life.
The Chihuahuan desert is found mainly in Mexico but reaches north to Albuquerque, New Mexico, so we spent some time in it too.
One of the things that struck me about the desert was the amazing way that plants grow there. If you have a pine forest, unlike our pine forests, the trees are not crowded. They are well spaced. Where shrubs cover a mountainside, they do so in the most spotty of fashions. Vegetation never covers the ground, even where it grows best. The plants demand space from all around them—like snooty royalty.
The plants even want some separation from those fantastic rocks that I love so much. Usually they are found well-spaced, like surprisingly obedient school children. Willa Cather put it well. She said,
From the flat red sea of sand rose great rock mesas, generally Gothic in out-line, resembling vast cathedrals. They were not crowded together in disorder, but placed in wide spaces, long vistas between them. This plain might once have been an enormous city, all the smaller quarters destroyed by time, only the public buildings left.