FOREWORD
There is little doubt that humanity is in for turbulent times when it comes to water. Rising human demands against a finite supply are draining rivers, shrinking lakes, and depleting aquifers. In a world of seven billion people and growing, competition for water is intensifying to quench our thirst, grow our food, generate electricity, and manufacture all manner of consumer goods from cars to computers to cotton shirts.
On top of these demand-driven trends, the last century and a half of greenhouse-gas emissions and the concomitant rise in global temperatures are fundamentally altering the cycling of water between the sea, the atmosphere, and the land. Climate scientists warn of more extreme floods and droughts and of changing precipitation patterns that will generally make dry areas drier and wet areas wetter. In terms of water, the natural variability of the recent past will not be a reliable guide to the future. We have moved outside the bounds of “normal” to some new normal yet to be understood.
The recent decade of drought in the southwestern United States has thrown a spotlight on this region’s vulnerability to the changes that lie ahead. From 2000 to 2009, the Colorado River exhibited the lowest ten-year-running-average flow of any ten-year period in the past century. During that time, the capacity of giant Lake Mead—which stores water for nearly 30 million people and vast areas of farmland—fell from 96 percent to 43 percent. Climate scientists at the Scripps Institution of Oceanography have estimated that, within a decade, there is a 50 percent chance that Lake Mead will drop below the reservoir’s outlets.
It is sobering to realize that this current southwestern drought pales (at least so far) in comparison to the “mega droughts” that have occurred multiple times in the past—and that could occur again in the future. The warm “medieval drought” during the middle of the twelfth century lasted two decades and was more severe and widespread than any other in the Southwest over the past 1,200 years. It almost certainly factored into the decline and ultimate collapse of the Hohokam, an enterprising people who settled and farmed in the valleys of the Salt, Gila, Verde, and other rivers of southern Arizona. The Hohokam thrived for a thousand years—from 450 to 1450—and then disappeared as a distinct culture.
Today, in our technologically sophisticated world, it is easy to believe we are immune to such an outcome. But we have not been seriously tested. For the past century and a half, humanity has enjoyed a relatively benevolent climate. During this time, we built big dams to tame the earth’s rivers, diverted flows from one river basin to another, drained wetlands for farming, and built oasis cities in the desert. We have so successfully masked aridity that we have become imbued with a false sense of security about our water future.
In this engaging and enlightening book, B. Lynn Ingram and Frances Malamud-Roam peer deep into the past through the lens of paleoclimatology to assemble evidence that can inform how citizens and leaders prepare for the new climatic regimes, including more intense droughts and floods, that almost certainly lie ahead for the western United States. The insights they uncover through this climate detective work lead them to a sense of urgency about taking action now to prepare for more erratic and extreme future conditions.
We may have other lessons to learn from the past as well. In order for our modern culture to enjoy a millennium of prosperity in the West, as the Hohokam did, we may need to embrace aridity and water’s tightening limits and apply ingenuity and creativity to successfully live within those limits, rather than continue to mask and deny them.