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. It is the most important waterway in the American Southwest. Rising temperatures could reduce the flow by more than a third by the end of the century. This is according to two scientists.
 
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. This is according to hydrology researchers Brad Udall of Colorado State University and Jonathan Overpeck of the University of Arizona.
 
Their study was 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.
 
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. This was as of Feb. 23.
 
For their study, Udall and Overpeck analyzed temperature, precipitation and water volume in the basin. They looked at data from 2000 to 2014. They compared it with historical data. That included a 1953-1967 drought. Temperature and precipitation records date to 1896. River flow records date to 1906.
 
Temperatures in the 2000-2014 period were a record 1.6 degrees Fahrenheit above the historical average. Meanwhile, precipitation was about 4.6 percent below, they said.
 
The researchers used existing climate models. They said that much decline in precipitation should have produced a reduction of about 11.4 percent in the river flow. But not in the 19.3 percent that occurred.
 
They concluded that the rest was due to higher temperatures. The temperatures increased evaporation from water and soil. The temperatures sucked more moisture from snow. And, they sent more water from plant leaves into the atmosphere.
 
Martin Hoerling is a meteorologist at the National Oceanic and Atmospheric Administration. He was not involved in the study. He 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. That was compared with 1.6 degrees during the 2000-2014 period.
 
Udall said climate scientists can predict temperatures with more certainty than they can precipitation. 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 (33)
  • bnora-dav
    3/02/2017 - 05:04 p.m.

    I think that global warming is a major problem because of this. Global warming is caused by the destruction of the ozone layer. Global warming is effecting many peoples lives.The article says, "The river supplies water to about 40 million people and 6,300 square miles of farmland." The drought will effect these peoples lives drastically. The article also says, "Global warming is already shrinking the Colorado River. It is the most important waterway in the American Southwest." If global warming increases, peoples lives will be severely changed.

  • smattison-dav
    3/03/2017 - 07:58 a.m.

    I think that its bad that the snow that they get is not producing enough water when it melts. Snow is just frozen water thats smaller. They need the water to grow plants and with out it the will start to starve. I think that global warming is affecting this.

  • metau-cel
    3/06/2017 - 10:13 a.m.

    since 2000 a drought has caused to Colorado River to drop 19%, global warning has had a great impact on this. The river is decreasing in size due to the fact that not enough snow is being produced because it is so warm so there isn't a lot of runoff into the river. Warming caused by climate change in this century will dwarf any warming caused by drought. 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

  • richardk-orv
    3/06/2017 - 04:39 p.m.

    the warmer water takes lots of water and gives little water out from the clouds. Also, it's going to take a long time to melt the snow. When the water fall on the mountain and since the top of the mountain is cold the water turns into snow.

  • joeg-orv
    3/07/2017 - 11:53 a.m.

    that picture is insane, it looks like the water level dropped 30 feet. Its so cool how you can see exactly where the water used to be because of the difference in color.

  • lukeh-orv
    3/07/2017 - 12:42 p.m.

    The warmer temperatures don't produce more snow runoff because The temperatures suck the moisture from snow.According to the text Global warming is shrinking river vital to 40,000,000 people it said,''The temperatures sucked more moisture from snow.And,they sent more water from plants leaves into the atmosphere.''That is why warmer temperatures don't produce more snow runoff.

  • samanthas-1-ste
    3/10/2017 - 01:14 p.m.

    When the temperature warms up, the snow melts. Usually the snow is on mountains so it could actually cause more mud slides. Sometimes when the snow melts around my sisters house it causes more mud slides than anything.

  • jacklynt-ste
    3/10/2017 - 01:29 p.m.

    I think that global warming is basically from humans. We caused global warming and now we have to suffer the consequences. This is going to become a huge problem when we do not have anymore water.

  • FernandoM70
    3/10/2017 - 09:02 p.m.

    Warmer temperatures don't produce more snow runoff
    because there is barley any snow falling.

    In the start of the passage it said there was not rain or snow.

    I think this because when it starts to snow it melts because of the warm temperature . I also think this because it is very hot were the river is.

  • NicolasP
    3/10/2017 - 10:13 p.m.

    Warmer temperatures don't produce more snow runoff because the temperatures have been increasing and the precipitation has been decreasing. Due to global warming. Which makes it harder for the snow to runoff rather than melt. The evidence I used was in paragraphs two and nine. This is where the paragraphs explain that there has been less precipitation and warmer temperatures. Mainly due to the possibility of global warming.

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