Colorado is globally recognized for its towering, snow-capped mountains, famous ski resorts, and high-altitude cities like Denver. This image often overshadows the state’s true climatic nature. The reality is that large portions of Colorado are fundamentally dry, a fact central to the state’s geography and ecology. To understand how much of Colorado is a desert, it is necessary to establish a clear, scientific definition of what a desert actually is.
Defining Aridity and Desert Climates
A region is classified as a desert not simply by temperature or the presence of sand, but by a chronic lack of available moisture. The most precise scientific measure of aridity compares precipitation to the atmospheric demand for water, known as potential evapotranspiration. Aridity is a permanent climatic feature where precipitation is consistently much less than the amount the air and ground could evaporate.
Climatologists classify a region as arid, or a true desert, if it receives less than 10 inches (250 millimeters) of annual precipitation. Semi-arid regions, often called steppes, receive between 10 and 20 inches (250 to 500 millimeters) of precipitation annually. Colorado features both of these conditions, which are distinct from hot deserts like the Sahara.
Many of Colorado’s dry areas are classified as cold deserts, combining aridity with high elevation and low temperatures. The overall lack of moisture is driven by the rain shadow effect and continental position, rather than extreme heat. Low humidity and high solar radiation also contribute to high rates of potential water loss.
Colorado’s Diverse Geographic Zones
Colorado’s complex topography is the primary driver of its varied moisture distribution, carving the state into three distinct climatic regions. The massive Rocky Mountains and the Continental Divide occupy the central portion, catching moisture from Pacific storms. This creates zones of high precipitation that feed the state’s rivers.
To the east are the expansive Eastern High Plains, which sit in a distinct rain shadow. The mountains strip the air of most moisture before it reaches the plains, resulting in a region dominated by semi-arid grasslands.
The Western Slope, including the Colorado Plateau and various basins, also experiences significant aridity. Local mountain ranges create multiple secondary rain shadows, leading to a patchwork of dry plateaus and canyons. This geographical structure determines where the state’s arid and semi-arid conditions are found.
Identifying and Quantifying Colorado’s Arid Regions
Quantifying Colorado’s desert land depends on whether the definition includes semi-arid regions or only true arid zones. The Eastern High Plains, which constitute nearly 40% of Colorado’s total land area, are predominantly classified as semi-arid steppe. Precipitation in this vast region typically ranges from 15 to 25 inches annually, supporting the short-grass prairie ecosystem.
The parts of Colorado that qualify as a true desert, receiving less than 10 inches of annual precipitation, are more localized but substantial. The most prominent example is the San Luis Valley in south-central Colorado, widely recognized as the highest-elevation true desert in the United States. This immense alpine valley, situated between the Sangre de Cristo and San Juan Mountains, receives an average of only about 7 inches of precipitation per year, classifying it as a cold desert.
Other arid pockets are found on the Western Slope, particularly in the deep, low-elevation basins and the Colorado Plateau country near the Utah border. Areas like the Colorado National Monument feature high desert canyons where the rain shadow effect supports xerophytic plant communities. The arid and semi-arid conditions across the state are characterized by distinct ecosystems, including sagebrush scrubland, pinyon-juniper woodlands, and the short-grass steppe. When considering both arid and semi-arid classifications, well over one-third of Colorado’s land area is characterized by a desert-like climate.