Eric Kuhn is the general manager of the Colorado River Water Conservation District. The River District is the largest and oldest of Colorado’s four conservation districts. It was chartered by the Colorado general assembly in 1937 to “preserve and conserve for Colorado, its Colorado River compact entitlement.” The district covers the Colorado River basin except for the San Juan and lower Dolores river basins. Kuhn began his employment with the district in 1981 and became manager in 1996.

Excerpt:

The prospect of climate-change–induced flow variations adds additional
uncertainty. While there is a wide range of results in the different published
studies, all suggest a future Colorado River with less streamflow. In a 2007
report, the National Research Council of the National Academies concluded
that “the preponderance of scientific evidence suggests that warmer future
temperatures will reduce future Colorado River streamflow and water supplies.”
In late 2008, the Colorado Water Conservation Board issued a synthesis
report on climate change specifically targeted toward water managers.
This report warns that “climate change will affect Colorado’s use and
distribution of water. Water managers and planners currently face specific
challenges that may be further exacerbated by projected climate changes.”
The study concludes that “all recent hydrologic projections show a decline
in runoff for most of Colorado’s rivers.”

Given the current demands on Colorado River water resources, even
a small change in the mean natural flow at Lee’s Ferry will cause serious
problems. Among the most optimistic of the climate-impact studies published
is the 2006 paper by Niklas Christensen and Dennis Lettenmaier.
This study suggested modest reductions in the mean flow at Lee’s Ferry in
the range of 6 to 10 percent. Most recently, a project by the Western Water
Assessment to narrow the results of the various studies suggests the floor for
the estimated flow reduction is about 10 percent.

Three credible studies that model the current operation of the Colorado
River with a sustained 10 percent reduction on natural flow at Lee’s Ferry?
The recent environmental impact statement (EIS) on the lower basin shortage
criteria included an alternative hydrology appendix that used estimated
flows at Lee’s Ferry published by Connie A. Woodhouse, David M. Meko,
and Stephen T. Gray in 2006. The paleohydrology-based trace for the period
from 1620 to 1674 is illustrative. This period has an estimated mean flow
at Lee’s Ferry of approximately 13.5 maf per year. The model output shows
a number of unacceptable and shocking results. For example, the Central
Arizona Project (CAP) would experience forty-seven straight years of shortages,
including a number of individual years when the project would divert
no water at all. Lake Mead would drop below and stay below the minimum
level for the Las Vegas Valley Water District to pump water to its customers
(1000’msl) for a period of close to twenty years. California, which has the
most senior of the prior perfected rights in the lower basin, would experience
occasional large shortages.

In the upper basin, Lake Powell would operate below the minimum
storage level necessary to produce hydroelectric power over 60 percent of
the fifty-year period, and there were two periods, one of five years and one
of twelve years, when Lake Powell would be empty and the upper-division
states would have been unable to meet their obligations to the lower basin
under the 1922 Colorado River Compact.

The lesson is that without major changes in how we currently manage
the Colorado River, even a modest decrease in system streamflows on the
order of 10 percent could cause significant unacceptable impacts throughout
the basin.