Global warming is shrinking river vital to 40,000,000 people In this April 16, 2013 file photo, a "bathtub ring" marks the high water mark as a recreational boat approaches Hoover Dam along Black Canyon on Lake Mead, the largest Colorado River reservoir, near Boulder City, Nev. Scientists say global warming may already be shrinking the Colorado River and could reduce its flow by more than a third by the end of the century. (AP Photo/Julie Jacobson, file)
Global warming is shrinking river vital to 40,000,000 people
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Global warming is already shrinking the Colorado River, the most important waterway in the American Southwest. It could reduce the flow by more than a third by the end of the century, two scientists say.
 
The river's volume has dropped more than 19 percent during a drought that has gripped the region since 2000. A shortage of rain and snow can account for only about two-thirds of that decline, according to hydrology researchers Brad Udall of Colorado State University and Jonathan Overpeck of the University of Arizona.
 
In a study published in the journal Water Resources Research, they concluded that the rest of the decline is due to a warming atmosphere induced by climate change. The change is drawing more moisture out of the Colorado River Basin's waterways, snowbanks, plants and soil by evaporation and other means.
 
Their projections could signal big problems for cities and farmers across the 246,000-square-mile basin. The area spans parts of seven states and Mexico. The river supplies water to about 40 million people and 6,300 square miles of farmland.
 
"Fifteen years into the 21st century, the emerging reality is that climate change is already depleting the Colorado River water supplies at the upper end of the range suggested by previously published projections," the researchers wrote. "Record-setting temperatures are an important and underappreciated component of the flow reductions now being observed."
 
The Colorado River and its two major reservoirs, Lake Mead and Lake Powell, are already overtaxed. Water storage at Mead was at 42 percent of capacity Feb. 22. Powell was at 46 percent.
 
Water managers have said that Mead could drop low enough to trigger cuts next year in water deliveries to Arizona and Nevada. They would be the first states affected by shortages under the multistate agreements and rules governing the system.
 
But heavy snow in the West this winter may keep the cuts at bay. Snowpack in the Wyoming and Colorado mountains that provide much of the Colorado River's water ranged from 120 to 216 percent of normal as of Feb. 23.
 
For their study, Udall and Overpeck analyzed temperature, precipitation and water volume in the basin from 2000 to 2014. They compared it with historical data, including a 1953-1967 drought. Temperature and precipitation records date to 1896 and river flow records to 1906.
 
Temperatures in the 2000-2014 period were a record 1.6 degrees Fahrenheit above the historical average, while precipitation was about 4.6 percent below, they said.
 
Using existing climate models, the researchers said that much decline in precipitation should have produced a reduction of about 11.4 percent in the river flow, not the 19.3 percent that occurred.
 
They concluded that the rest was due to higher temperatures, which increased evaporation from water and soil, sucked more moisture from snow and sent more water from plant leaves into the atmosphere.
 
Martin Hoerling, a meteorologist at the National Oceanic and Atmospheric Administration who was not involved in the study, questioned whether the temperature rise from 2000 to 2014 was entirely due to global warming. Some was likely caused by drought, he said.
 
Udall said warming caused by climate change in this century will dwarf any warming caused by drought. He noted that during the 1953-1967 drought, the temperature was less than a half degree warmer than the historical average, compared with 1.6 degrees during the 2000-2014 period.
 
Udall said climate scientists can predict temperatures with more certainty than they can precipitation, so studying their individual effects on river flow can help water managers.
 
Rain and snowfall in the Colorado River Basin would have to increase 14 percent over the historical average through the rest of the century to offset the effect of rising temperatures, he said.
 
"We can't say with any certainty that precipitation is going to increase and come to our rescue," Udall said.

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CRITICAL THINKING QUESTION
Why don't warmer temperatures produce more snow runoff?
Write your answers in the comments section below


COMMENTS (8)
  • vaneises-
    3/03/2017 - 08:39 a.m.

    Warmer temperatures don't produce more snow runoff because due to higher temperatures, which increased evaporation from water and soil, sucked more moisture from snow and sent more water from plant leaves into the atmosphere. If there isn't enough moisture in the snow then there wont be enough snow runoff.

  • irisp-ste
    3/06/2017 - 09:06 a.m.

    This topic is something that many people often want to overlook, even though there is real evidence that global warming is starting to have effects on our environment. If nothing is done to preserve precipitation and maintain the river levels, many animals and plants will face devastating effects. Hopefully environmentalists and scientists can discover a way to preserve the famous river.

  • daltons1-ste
    3/09/2017 - 01:30 p.m.

    Global warming is a real concern and if people don't accept that then we will tear our own world apart figuratively of course. Global warming can kill wildlife and as we can see it can replenish water supplies. A certain 45th president has an awful stance on this matter.

  • kaileew-ste
    3/10/2017 - 01:30 p.m.

    The Colorado river is shrinking due to global warming. The volume of the river has dropped more than %19. I wonder how else global warming will hurt the Earth.

  • bradl-pla
    3/13/2017 - 10:09 p.m.

    The Colorado river has drastically reduced in flow in the past few years, and is projected to decline further. A major drought since 2000 has caused the river's reservoirs to operate under 50% capacity as of 2017. A large portion of this draught has also been caused by raising temperatures due to climate change. Even with the increase precipitation in the last year, there would have to be a 14% increase in overall precipitation for the rest of the century in order to prevent shortages. This has huge ramifications on our society, as humans need water to survive. Without the water from the Colorado river, farmlands would run dry and people would have little water. The shortage also impacts the environment as it supplies wildlife in the Grand Canyon in addition to humans. An interesting fact that this article did not bring up is that if there are water shortages, California negotiated the water agreement to exempt itself from cuts. This could make cause major controversy if the cuts are ever emplaced.

  • makenziev-pla
    3/16/2017 - 02:02 p.m.

    This article mainly talks about how global warming is causing an accelerated decrease in the water level of the Colorado River. This is one of the most important waterways in the country (it affects 7 US states). This affects civil engagement because global warming is said to be caused by humans and it is important that as a society, we attempt to stop global warming so that it doesn't further affect the water levels in not only the Colorado River, but also other rivers around the world. Scientists are looking for possible ways to reverse this decrease, but at this point there is not much that we can do besides do our best to slow global warming.

  • noahr-ste
    3/24/2017 - 12:49 p.m.

    The warmer temperatures are drying up rivers all over the world not just the Colorado river. The Colorado river though has lost 19% of its water. Hopefully they will take notice to this issue and fix it.

  • derrickc-pay
    3/27/2017 - 09:50 a.m.

    Warmer temperatures don't produce more snow runoff due to higher temperatures, which increase evaporation from water and soil, suck more moisture from snow and sent more water from plant leaves into the atmosphere.

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