by Robert Marcos, photojournalist
While climate change and the general lack of precipitation are the most obvious causes of the aridification of the American West, there are other factors taking place in the background that are contributing to this process.
Dust on Snow: Windblown dust from disturbed desert soils and dry lake beds—such as the Great Salt Lake—settles on mountain snowpacks. This “dark topcoat” reduces reflectivity (albedo), causing snow to absorb more solar heat and melt up to three to seven weeks earlier than clean snow. This premature runoff often reaches reservoirs when they are already full or when the ground is still too frozen for agricultural use, effectively wasting the “natural reservoir” of the snowpack.1
Vapor Pressure Deficit (VPD): Often described as the “thirst of the atmosphere,” VPD measures the difference between the moisture in the air and how much it can hold. Higher temperatures exponentially increase this demand, sucking moisture directly out of soils and plants even when precipitation levels are normal. In recent years, this “atmospheric thirst” has accounted for roughly 61% of drought severity, outweighing the impact of reduced rainfall.2
Pacific Decadal Oscillation Stagnation: The “PDO” is a long-term ocean temperature pattern that typically flips every 20 years. Since the 1990s, it has remained stuck in a “negative phase,” which brings cooler water to the eastern Pacific and pushes moisture-bearing storms farther north, away from the Southwest. Recent research suggests this prolonged “stuck” phase may be driven by human-caused aerosol and greenhouse gas emissions.3
Soil and Vegetation Feedbacks: Aridification creates a self-reinforcing cycle. As soils dry out, they lose the cooling effect of evaporation, causing solar radiation to heat the ground and the air even further. Additionally, while higher CO2 levels can make plants more water-efficient, this gain is often offset by longer growing seasons and increased plant growth, which ultimately draws more total moisture from the soil through transpiration.4
Land Use and Soil Degradation: Intensive land uses, including livestock grazing and urbanization, remove protective vegetation and destabilize soil. This not only increases wind erosion (leading to more dust-on-snow events) but also reduces the soil’s ability to absorb and retain what little moisture does fall, intensifying the “baking” of the landscape.5
Invasive plants: Cheatgrass, tamarisk, and Russian olive are invasive plants most often named as contributors to the aridification of the American West. Cheatgrass transforms diverse, deep‑rooted native shrub–grass communities into shallow‑rooted, flammable annual monocultures that dry and senesce early, it depletes shallow soil moisture sooner in the growing season, and dramatically increases fire frequency. It creates a cheatgrass–wildfire feedback loop that repeatedly removes perennial vegetation, reduces soil organic matter and carbon storage, accelerates erosion, and leaves soils warmer, drier, and less able to retain water, so landscapes lose both plant cover and hydrologic function and effectively behave more like a hotter, drier, impoverished system even when long‑term precipitation totals have not changed.6