Colorado River water shortage declared
BOULDER, COLO. • Low water in the Colorado River’s largest reservoir triggered the first federal declaration of a shortage on Monday, a bleak marker of the effects of climate change in the drought-stricken American West and the imperiled future of a critical water source for 40 million people.
“We are seeing the effects of climate change in the Colorado River basin through extended drought, extreme temperatures, expansive wildfires, and in some places, flooding and landslides,” said Tanya Trujillo, the Interior Department’s assistant secretary for water and science.
The declaration of a socalled Tier 1 shortage was expected on a river whose flows have been overallocated for a century and rapidly declining since 2000, and it was staved off by agreements under which states cut their water use. But the announcement still came as a blow at the end of a summer of extraordinary heat, as well as a harbinger for further cuts.
“This drought is like a boa constrictor. It just keeps getting tighter every year,” said Tom Davis of the Agribusiness and Water Council of Arizona. Davis said he still has hope for drought-ending precipitation, but he is alarmed.
“It is a sobering thing to realize we are at Tier 1 already,” Davis said. “A few years ago, no one was thinking this would happen. It’s damn sure got our attention.”
The river starts in the Rocky Mountains of Colorado and snakes southwest for 1,450 miles (2,330 kilometres), its waters dammed and diverted along the way to irrigate fields and lawns and deliver water to industry, cities and taps. States and Mexico divvy up its waters under complex system first agreed to in 1922, but the flow has rarely been sufficient. Allocations were made following a period of unusually heavy precipitation, meaning “we’ve been living beyond our means in terms of water delivery compared to water available,” said Sharon Megdal, a University of Arizona water expert.
A 22-year-long drought — the region’s most severe in more than a millennium — and climate change have made that fundamental problem worse. The alpine snowpack that feeds the river has been diminishing and melting earlier in the year. Parched soil soaks up much of it before it even enters rivers and streams. Extreme heat evaporates water in Lake Mead and other reservoirs more quickly and causes evaporation from plants.
Brad Udall at Colorado State University said about half the decline in the river’s average annual flow — which has fallen 20 per cent per cent compared to the last century — is attributable to rising temperatures and half to declines in precipitation. He and other scientists say “drought” is no longer the appropriate word to describe the climate in the West. Instead, they say, it is aridification — a long-term, more permanent desiccation.