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Warm Deserts

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Map Legend & Subregion List

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NameColor on MapCEC Code*
Mojave Basin and Range10.2.1
Chihuahuan Deserts10.2.4
Sonoran Basin and Range10.2.2
Baja Californian Desert10.2.3

* This code refers to the CEC's Level 3 ecoregion codes for North America, see here.

About the Warm Deserts

The Warm Deserts are a level II ecoregion of North America consisting of two discontinuous pieces. The westeren portion extends from Nevada and southwest Utah through California and Arizona into most of Baja California and Sonora. The eastern portion is mostly located in Mexico, east of the Sierra Madre Occidental mountain range, extending north into west Texas and southern New Mexico.

Unlike the Cold Deserts which are mostly produced by rain shadow, the western portion of this region, opening to the ocean, largely results from a persistent high-pressure system off the coast of California. This system diverts moisture-laden weather systems to the north and south as they come inland. This region thus has a diversity of inland areas with drier air, to coastal areas with more moderate temperatures and higher relative humidity but very low rainfall. The Eastern portion of this region is produced by rain shadow, much like the cold deserts.

Vegetation cover varies considerably throughout this region. Some regions are dominated by large cacti, whereas in others, grasses are more dominant. Much of the vegetation here is adapted to utilize short bursts of high water availability, going dormant for months at a time, and then becoming active in response to the presence of water. Plant diversity is often higher than in the cold deserts, owing to the greater portion of plants able to survive in the warmer temperatures, but the higher temperatures can also produce additional stress from heat and drought.

Different partsr of this region border radically different ecoregions. To the west, this region transitions gradually into Mediterranean California, as the rainfall increases slightly and the desert becomes Chapparral. To the north, as temperatures cool, the western portion transitions smoothly to Cold Desert, but east of the rockies, the desert transitions to the relatively-moister South Central Semi-Arid Prairies. Southeast of the Sonoran desert, the region transitions to tropical dry forests of the Western Pacific Coastal Plain, Hills, and Canyons, and in Baja California, to the Sierra and Plains of El Cabo.

Mountain ranges and changes in altitude produce more abrupt borders with the Western Sierra Madre Piedmont, and in the north, the Upper Gila Mountains.

Historically, this region was sparsely populated, but more recently, the population has exploded in the major cities. The largest metro areas in this region include Phoenix, AZ, Las Vegas, NV, the cross-border metro of El Paso-Juaréz, and Torreón, Coahuila. Water diversion both for urban use and agriculture has severely reduced the flow of water in the major rivers of this region, especially the Colorado river, devastating the ecosystem in the Gulf of California.