While reflecting on his 12-year term as governor of Colorado, Richard Lamm recalled that his “most terrifying” day in office was the one he spent at Colorado State University learning about tree rings.1 Around that time, the late 1970s, the state’s water needs were becoming more and more difficult to manage under the auspices of the Colorado River Compact, the 1922 agreement that allocated the river’s water rights among seven western states. Water scarcity had led the states to create a complex physical and legal infrastructure to store, distribute, and manage the natural resource. But the reservoirs and diversions had been constructed to suit a 20th-century climate. When Lamm got a glimpse beyond that narrow historical window, he was frightened by what he saw.
The tree-ring scientists explained that before Colorado attained statehood in 1876, it and the broader region had been struck by several droughts that endured for...
