The Chihuahuan Desert
A desert region can be defined many ways. To a physical scientist such as a meteorologist, a desert is defined as an area receiving an average annual precipitation (a combination of rainfall, snow, and other forms of moisture) of 10 inches or less. However, to a biologist, it is not necessarily how much precipitation is received but rather how that moisture moves through an ecosystem and the effect it will have on life forms that defines a desert.
One way to understand the way moisture moves through an ecosystem is to look at how much moisture could be potentially lost through evaporation and compare it to how much moisture is gained through precipitation. Potential evaporation or potential evapotranspiration is defined as the amount of evaporation that would occur if sufficient water is available. Many different factors—such as surface and air temperatures, the amount of solar radiation, and wind—all affect how much water will evaporate from the surface. Desert regions are typically hot, windy, and sunny, making potential evapotranspiration rates high. On the other hand, moisture gain through precipitation is typically low.
For example, at the Chihuahuan Desert Nature Center, our average annual precipitation is 17 inches. Our average annual potential evapotranspiration is 36 to 48 inches!
Many scientists, such as biologists, define a desert region as an area in which the evaporation rate exceeds the average annual precipitation. Typically, though, a desert region is defined by a combination of factors such as climate, topography, and plant and animal communities.
The Chihuahuan Desert region stretches from the Rio Grande Valley in southern New Mexico and the San Simon Valley of southeastern Arizona to an area just north of Mexico City—an area approximately 800 miles long and 250 miles wide. Included in the Chihuahuan Desert are parts of the states of Arizona, New Mexico, and Texas in the United States, as well as parts of the states of Chihuahua, Coahuila, Nuevo Leon, Durango, Zacatecas, and San Luis Potosi in Mexico.