There is no one definition of a desert that is accepted by all. The boundaries of the Chihuahuan Desert, like those of most other deserts, change radically depending on the definition accepted. Some definitions are based on various climatic factors, while others combine climatic and biotic features, and some rely solely on vegetation and/or animal life. Morafka (1977a:3-4) points out that, "The desert has been analyzed and defined ecologically, at least in English literature, largely from its unstable and atypical grassland ecotones lying within the United States boundaries." He goes on to note that this would be similar to analyzing the contents of an egg by extrapolating from a shell sample. Things have improved in the over 20 years since this assessment, but the Chihuahuan Desert still remains North America's poorest known desert.
As a basis for discussion for this web site, the boundaries of the Chihuahuan Desert as defined by Schmidt (1979) have been adopted, while keeping in mind that there are other defensable geographic limits.
Schmidt's definition is based on de Martonne's Index of Aridity as set forth in the English language version (de Martonne, 1927), and Schmidt's discussion is used as the basis for the following comments.
The Index of Aridity is obtained from the formula Ia = Pmm/T°C+10, where "Pmm" is annual precipitation in millimeters and T°C is average annual temperature in degrees Celsius. The lower the index, the more arid the climate. de Martonne considered true deserts to correspond to an index of less than 5, with dry steppes from about 5 to about 10. Schmidt considered as desert those areas having an index equal to or less than 10. His boundaries are based on data from almost 800 weather stations in the southwestern U.S. and northern Mexico, with about 115 of these being within the finally determined bounds of the desert.
Schmidt (1979) illustrated a dozen concepts of the Chihuahuan Desert. Sketches of these "many deserts," adapted from Schmidt's works, are shown in figures 1, 2, and 3. Morafka's (1977b) version of a map of the Chihuahuan Desert also is shown.
As time permits, fuller discussions of the criteria used by various authors will be accessible from the map pages.
Last Update: 24 December 1999.