There are more than 75,000 dams in the United States, and the largest five reservoirs by storage capacity lie west of the 100th meridian. Today dams, irrigated agriculture, and large cities are the hallmark of western US landscapes. Indeed, irrigation was necessary to create a sustainable society in the western United States. * Notably, Powell remarked that irrigation would be required in the arid region west of the 100th meridian, to make the parcels provided by the Homesteading Act livable ( 3). The assumption of adequate freshwater in the western United States was justified by the prevailing view of hydroclimate, which included a theory that agriculture would stimulate rainfall, or “rain would follow the plow.” Early stewards of freshwater resources-like John Wesley Powell-warned that the American West was a desert, only a small fraction of which could be sustainably reclaimed ( 1). Manifest Destiny and the westward expansion of European civilization in the United States during the 19th century were predicated on an adequate freshwater supply. We close with a prospectus for reclaiming freshwater sustainability in the Cadillac Desert, including a suite of recommendations for reducing region-wide human appropriation of streamflow to a target level of 60%. Thus, Reisner's incisive journalism led him to the same conclusions as those rendered by copious data, modern scientific tools, and the application of a more genuine scientific method. More broadly, we estimate that the equivalent of nearly 76% of streamflow in the Cadillac Desert region is currently appropriated by humans, and this figure could rise to nearly 86% under a doubling of the region's population.

Our analysis provides strong scientific support for many of Reisner's claims, except the notion that reservoir storage is imminently threatened by sediment.

Here we evaluate these claims using the best available data and scientific tools. Reisner's analysis paints a portrait of region-wide hydrologic dysfunction in the western United States, suggesting that the storage capacity of reservoirs will be impaired by sediment infilling, croplands will be rendered infertile by salt, and water scarcity will pit growing desert cities against agribusiness in the face of dwindling water resources. Marc Reisner tackles this theme in his 1986 classic Cadillac Desert: The American West and Its Disappearing Water. Increasing human appropriation of freshwater resources presents a tangible limit to the sustainability of cities, agriculture, and ecosystems in the western United States.

Cadillac Desert by Marc Reisner