Rising Temperatures Threaten Viability Of Colorado River

Rising temperatures are amplifying the effects of recent drought on the Colorado River, which plays a key role in the health of national parks such as Canyonlands and Grand Canyon, according to a U.S. Geological Survey report.

Rising temperatures have been playing an increasingly important role in Colorado River streamflow in recent decades, amplifying the negative effects of drought and dampening the positive effects of wet winters.

Snow-fed rivers such as the Colorado rely heavily on winter precipitation. But warming temperatures since the 1980s have meant that less snow accumulates and snowpack melts earlier, both of which reduce streamflow.

As a result, river managers and those who depend on the river need to factor rising temperatures into streamflow calculations.

"Forecasts of streamflow are largely based on precipitation,” said Connie Woodhouse, who led a USGS team that examined the effect of rising temperatures on streamflow. “What we’re seeing since the 1980s is that temperature plays a larger role in streamflow and in exacerbating drought." 

That conclusion was based on "records of streamflow, temperature, soil moisture, and precipitation in the upper Colorado River basin going back more than 100 years."

The health of the Colorado River long has been monitored. Back in 2011, the National Parks Conservation Association published a report that looked at how dams along the river were impacting parks.

The series of dams that interrupt the Colorado River in its flow from the high country of Rocky Mountain National Park down to the Gulf of California has altered nature by constricting high runoff flows, artificially enhancing low flows, changing sedimentation patterns, and even impacting water temperatures to the detriment of native fisheries, said the report, National Parks of the Colorado River Basin, Water Management, Resource Threats, and Economics.

In the 76-page report the park advocacy group pointed to a number of findings:

* Large dams in the Colorado River Basin have had and continue to have significant and far-reaching impacts on natural and cultural resources in national parks along the Colorado River and its tributaries. Because of these dams, rivers are now characterized by highly unnatural flow regimes rather than natural hydrological cycles.

* Dams fragment the Colorado River system and interfere with natural ecological processes in national parks.

* Dams and reservoirs have profoundly changed the appearance and sounds of the Colorado River and several of its major tributaries as they flow through national parks.

* Changes in river temperatures and habitats wrought by dams have contributed significantly to declines in native fish populations.

* Dams affect prehistoric and historic cultural resources within national parks.

As a result of dams, how visitors experience the rivers in the Colorado River system is changed, the group said. For instance, the existence of Flaming Gorge Dam upstream of Dinosaur National Monument controls the Green River to such a degree that, "The deafening roar of the spring flood through the Canyon of Lodore in Dinosaur National Monument is subdued to the point that the sound no longer conveys a sense of the power that created this very place."

At Grand Canyon National Park, of course, the existence of the Glen Canyon Dam just upstream has greatly subdued peak flows that once reached 120,000 cubic feet per second and higher, and led to issues with sandbar creation and fisheries impacts, the report noted.

In Black Canyon of the Gunnison National Park, riparian areas that normally would not be allowed to form due to scouring by spring runoff have developed, it added.

And, of course, the Glen Canyon Dam has created Lake Powell, a manmade reservoir that has inundated many culturally rich and scenically beautiful side canyons.

Despite recognition from Maj. John Wesley Powell back in 1879 that there was too little water in the West to support large populations, the country's ever-constant expansion has created insatiable, and perhaps unreasonable, demands on the Colorado to nourish communities and crops and to generate hydropower.