The Sonoran Desert is clearly distinct from nearby deserts (e.g., the
Great Basin,
Mojave, and
Chihuahuan deserts) because it provides subtropical warmth in winter and two seasons of rainfall (in contrast, for example, to the Mojave's dry summers and cold winters). This creates an extreme contrast between aridity and moisture.[4]
Location
The Sonoran desert wraps around the northern end of the
Gulf of California, from
Baja California Sur (
El Vizcaíno Biosphere Reserve in central and Pacific west coast, Central Gulf Coast subregion on east to southern tip), north through much of
Baja California, excluding the central northwest mountains and Pacific west coast, through southeastern California and southwestern and southern Arizona to western and central parts of
Sonora.[5]
To the north in California and northwest Arizona, the Sonoran Desert transitions to the colder-winter, higher-elevation
Mojave,
Great Basin, and
Colorado Plateau deserts.
The desert's sub-regions include the
Colorado Desert of southeastern California; and the
Yuma Desert east of the north-to-south section of the
Colorado River in southwest Arizona. In the 1957 publication Vegetation of the Sonoran Desert, Forrest Shreve divided the Sonoran Desert into seven regions according to characteristic vegetation: Lower Colorado Valley, Arizona Upland, Plains of Sonora, Foothills of Sonora, Central Gulf Coast, Vizcaíno Region, and Magdalena Region.[6] Many ecologists consider Shreve's Vizcaíno and Magdalena regions, which lie on the western side of the
Baja California Peninsula, to be a separate
ecoregion, the
Baja California desert.
The Sonoran desert has an
arid subtropical
climate and is considered to be the most
tropical desert in
North America.[8] In the lower-elevation portions of the desert, temperatures are warm year-round, and
rainfall is infrequent and irregular, often less than 90 mm (approx. 3.5”) annually. The
Arizona uplands are also warm year-round, but they receive 100–300 mm (approx. 4-12”) of average annual rainfall, which falls in a more regular bi-seasonal pattern.[2]
Many plants not only survive, but thrive in the harsh conditions of the Sonoran Desert. Many have evolved to have specialized adaptations to the desert climate. The Sonoran Desert's bi-seasonal rainfall pattern results in more plant species than any other desert in the world.[2] The Sonoran Desert includes plant genera and species from the
agave family,
palm family,
cactus family,
legume family, and numerous others. Many of these adaptations occur in food crops.
Mission Garden is a living agricultural museum that showcases foods that have been grown in the Sonoran Desert for over 4000 years.
The Sonoran is the only place in the world where the famous
saguaro cactus (Carnegiea gigantea) grows in the wild.[10]Cholla (Cylindropuntia spp.),
beavertail (Opuntia basilaris),
hedgehog (Echinocereus spp.),
fishhook (Ferocactus wislizeni),
prickly pear (Opuntia spp.),
nightblooming cereus (Peniocereus spp.), and
organ pipe (Stenocereus thurberi) are other taxa of cacti found here. Cactus provides food and homes to many desert mammals and birds, with showy flowers in reds, pinks, yellows, and whites, blooming most commonly from late March through June, depending on the species and seasonal temperatures.
Ascending from the valley up
bajadas, various subtrees such as
velvet mesquite (Prosopis velutina),
palo verde (Parkinsonia florida),
desert ironwood (Olneya tesota),
desert willow (Chilopsis linearis ssp. arcuata), and
crucifixion thorn (Canotia holacantha) are common, as well as multi-stemmed
ocotillo (Fouquieria splendens). Shrubs found at higher elevations include
whitethorn acacia (Acacia constricta), fairy duster, and
jojoba. In the desert subdivisions found on Baja California, cardon cactus, elephant tree, and
boojum tree occur.[11]
The Sonoran Desert is home to a wide variety of animals, birds and other creatures, such as the
Gila monster,
bobcat,
mule deer,
antelope jackrabbit,
burrowing owl,
greater roadrunner,
western diamondback rattlesnake, and
elf owl. There are three hundred fifty bird species, 20 amphibian species, over 100 reptile species, 30 native fish species, over 1000 native bee species, and more than 2,000 native plant species found in the desert area.[13] The Sonoran Desert area southeast of
Tucson and near the Mexican border is vital habitat for the only population of
jaguars living within the United States.[14] The
Colorado River Delta was once an ecological hotspot within the Sonoran desert due to the Colorado river in this otherwise dry area, but the delta has been greatly reduced in extent due to the damming and use of the river upstream. Species that have higher heat tolerance are able to thrive in the conditions of the Sonoran Desert. One such insect species that has evolved a means to thrive in this environment is Drosophila mettleri, a Sonoran Desert fly. This fly contains a specialized
P450 detoxification system that enables it to nest in the cool region of exudate moistened soil. Thus, the fly is one of few that can tolerate the high desert temperatures and successfully reproduce.
The largest city in the Sonoran Desert is
Phoenix, Arizona, with a 2017 metropolitan population of about 4.7 million.[15] Located on the
Salt River in central Arizona, it is one of the fastest-growing
metropolitan areas in the United States. In 2007 in the Phoenix area, desert was losing ground to
urban sprawl at a rate of approximately 4,000 square meters (1 acre) per hour.[16]
The next largest cities are
Tucson, in southern Arizona, with a metro area population of just over 1 million,[17] and
Mexicali,
Baja California, with a similarly sized metropolitan population of around 1,000,000. The metropolitan area of
Hermosillo,
Sonora, has a population close to 900,000.
Ciudad Obregón,
Sonora, in the southern part of the desert, has a population of 375,800.[18]
During the winter months, from November to April, the daytime temperatures in the Coachella Valley range from 70 °F (21 °C) to 90 °F (32 °C) and corresponding nighttime lows range from 46 °F (8 °C) to 68 °F (20 °C) making it a popular winter resort destination. Due to its warm year-round climate
citrus and subtropical fruits such as mangoes, figs, and dates are grown in the Coachella Valley and adjacent
Imperial Valley. The Imperial Valley has a total population of over 180,000 and has a similar climate to that of the Coachella Valley. Other cities include
Borrego Springs,
Indio,
Coachella,
Calexico,
El Centro,
Imperial, and
Blythe.
Straddling the
Mexico–United States border, the Sonoran desert is an important migration corridor for humans and animals. The harsh climate conditions and border militarism mean that the journey can be perilous, usually moving at night to minimize exposure to the heat. [19]
^The
Sonoran Desert National Monument was created in 2001 in Arizona, to enhance protection of the unique resources of the Sonoran Desert, with 2,008 square kilometers (496,000 acres). :Reference:
Sonoran Desert National MonumentArchived 2009-01-26 at the
Wayback Machine, Bureau of Land Management, U. S. Department of the Interior. Accessed on line June 17, 2009.