Geoscience Reference
In-Depth Information
of the Colorado River basin predicts that the snowpack there could decrease
by 30 percent as early as 2050. h e headwaters of the river lie in the high
elevations of Colorado, Wyoming, and New Mexico. h e river then l ows
through the high Colorado Plateau, ultimately bringing precious water to
the lower desert states of Nevada, Arizona, and California. Under natural
conditions, the river would then drain through its delta into the Gulf of
California. Today, all of that water is spoken for and used before it ever
reaches the once-thriving delta, as discussed in chapter 12. For decades, every
drop has gone to sustaining a growing population and expanding agriculture
throughout this arid region.
h e stretch of the Colorado River in northern Arizona, between the
two largest reservoirs on the river (Lake Powell and Lake Mead), supplies
water to over 30 million people in major Southwest cities, including Los
Angeles, Phoenix, Las Vegas, and San Diego. Climate models of the region
predict that, over the next thirty to i t y years, the Colorado River system
will experience 10-30 percent reductions in runof as the result of climate
change. Marine physicist Tim Barnett and climate scientist David Pierce
at Scripps have incorporated these predictions into a water budget analysis
assessing the impacts of natural climate variability, future climate warming,
and water usage on the Colorado River basin. h eir results show a net dei cit
of almost one million acre-feet of water per year in that basin. At this rate,
they conclude, there is a 50 percent chance that both Lake Mead and Lake
Powell could reach “dead pool,” rendering them useless for hydroelectric
power generation or useful water storage, by as early as 2021. In the decade
between 1999 and 2009, the level of Lake Powell dropped by 60 percent of
its “full pool” capacity. h e falling reservoir level has exposed enormous
white calcium carbonate coatings, rising as high as ten-story skyscrapers
on the canyon walls, and these are likely to grow higher in the future (see
i g u r e 3 4 ) .
ecosystem impacts
As dii cult as these changes to our water supply will be on cities and agri-
culture, we must also consider the profound impacts of altered hydrology on
the West's ecosystems. At the University of California, Berkeley, ecologist
John Harte has been studying the consequences of global warming in the
American West. He has warned that, if all of the snow in mountains of the
