A Fragile Desert at the Mercy of Human Beings

The long, complex history of the Sonoran Desert demonstrates the intimate connection between geology, ecology, and human beings. Early human cultures depended utterly on the land and learned to survive by making the most of its whims and resources. For a time, it seemed that the Salado, Hohokam, and other desert civilizations had overcome the limitations of their desert home, with great irrigation works, complex civilizations, and farflung trade networks. But even those civilizations floundered, as a result of a combination of conflict, overpopulation, and the climatic cycles that have always shadowed the Sonoran Desert.

Now, the Sonoran Desert is the most populated desert in the world, with major cities like Phoenix and Tucson set in its heart. Those cities rely on a combination of ice age groundwater pumped out of wells hundreds of feet deep and water trapped in reservoirs and transported across hundreds of miles of desert in great canals. The dams and irrigation canals have destroyed or degraded an estimated 90 percent of desert riparian areas like the Gila River. Moreover, activities like cattle grazing have converted huge swaths of grassland into desert.

Meanwhile, the pollution-spurred warming of the planet could significantly increase the duration and severity of droughts, which tree-ring studies demonstrate could last 30 years or more even before the most recent rise in global temperatures. The rapidly growing cities of the Sonoran Desert are likely to face hard choices and grave challenges in the decades to come. Let's hope they have better luck than the Hohokam.