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What Climate Change in the Rockies Means for its Water

In the West, Colorado is known as a “headwaters” state because most of the region’s biggest rivers begin in the Colorado Rocky Mountains.

The Colorado River. The Arkansas River. The Rio Grande. The San Juan River. The Platte River — North and South. Altogether, they provide 19 states with drinking and irrigation water, including the cities of Los Angeles, Phoenix and Denver, among many others.

Dust on the snowpack in Colorado's San Juan Mountains. The dust, blown from deserts west of the mountains, speeds the melting of snow.
Credit: Jeffrey Deems/University of Colorado. 

All of the water in those rivers comes from one source: the Rocky Mountains’ snowpack, which is expected to shrink as temperatures rise in a warming climate.

That’s why a new report by Colorado’s state water authorities showing how climate change will affect water supply there is so important. How much water is going to be coursing down these rivers in a warming world is highly uncertain, and that means the millions of people downstream of Colorado have a lot at stake.

“Already, snowmelt and runoff are shifting earlier, our soils are becoming drier, and the growing season has lengthened,” Jeff Lukas, lead author of the report released by the Colorado Water Conservation Board and the Western Water Assessment, said in a statement. “Wildfires and heat waves have become more common, too. Climate projections suggest those trends — all of which can affect water supply and demand — will continue.”

Here are three things you should know about what Colorado’s new climate change report says about the future of where Westerners will get their water:

1. Nobody knows if it’s going to get wetter, drier or stay the same in Colorado’s mountains, but warming temperatures could mean that there will be less water available for people to use anyway.  

Climate models generally agree that the Rocky Mountains are going to get between 2.5°F and 5°F warmer though 2050, the report says, with summers warming more than winters, but there isn’t much agreement about whether they’ll be wetter or drier as the climate changes.

The climate models show a wide range of possible precipitation scenarios in Colorado’s mountains as temperatures rise, from a 5 percent decrease to an 8 percent increase in precipitation by 2050.

Regardless whether the mountains become wetter or drier, winter snowpack is likely to diminish as temperatures rise, and it could melt earlier. Mountain snow usually begins melting in early spring, peaking in June. But because of warmer temperatures, all that runoff could course through streams and rivers up to three weeks earlier by 2050, and it could melt much faster than normal.

Trail Ridge Road passes through Colorado's Rocky Mountain National Park in May 2012, when the snowpack had nearly disappeared at a time when it is usually many feet deep.
Credit: Bobby Magill

Warmer temperatures will mean plants will consume more water and the soil will be drier, reducing the amount of water that will run off the mountains and into streams.

Early runoff is a problem for water supplies because dams and reservoirs aren’t designed to capture large amounts of water that tumbles off the mountains quickly, making less water available in the summer when demand is at its highest. It could force water managers to redesign how reservoirs and dams operate and strain farmers’ irrigation water supply because it’s less likely to be available in the summer when it’s needed the most.

2. Desert dust blown on the snowpack is bad news for the West’s water supplies.

If you fly over Colorado’s mountains in the winter, there’s a chance that some of the snow you’ll see below will appear slightly brown or tan in color. What you’re seeing is dust that blew onto those snow fields from the deserts west of the mountains. The soil in those deserts, many stricken by drought, has been disturbed by oil and gas development, grazing and other uses, and it is easily blown onto the mountains in strong winds.

That’s bad news for water in the West because the dust that lands on mountain snow absorbs heat and melts the snow, causing runoff to occur weeks earlier than normal and plants to absorb more water from the soil as the snow disappears.

Already, dust blown onto the mountains in recent years has reduced overall runoff in the Upper Colorado River Basin of western Colorado by 5 percent compared to conditions 200 years ago.

3. It’s likely that the major rivers will carry less water in 50 years, but there is a lot of disagreement about that.

Increasing temperatures, dust on the snowpack and other climate change-related factors are likely to work together to reduce the total amount of water in many of the rivers that flow out of Colorado.

The major rivers that flow to the south — the San Juan and the Rio Grande rivers — are almost certain to see decreases in streamflow by 2050, the report says. But climate models are split about whether the state’s other rivers, including the Colorado, Arkansas and the South Platte rivers, will see reduced flows.

Either way, the the report says the odds are that less water will be flowing out of the state in a warmer climate. According to the Assessment of Climate Change in the Southwest United States, which became part of the National Climate Assessment, if climate change reduces the amount of water flowing in the Colorado River, downstream metropolises such as Phoenix and Tucson could face severe water shortages.   

In a warming world, water authorities may have to plan for extreme weather that they never planned for in the past — megadroughts that could dry up water supplies for many years or extreme flooding that could wash out or damage dams and pipelines.

So, the bottom line for the West’s long-term water supply, the report says, is that it’s going to be a lot more difficult to plan for how to secure water for growing cities in the future, and figuring climate change into water planning is going to be critical.

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Comments

By Bob (Cedar Rapids Ia 52404)
on August 12th, 2014

Just a hunch. But the chances of these predictions to occur by 2050 versus 2015 and any year hence appear the same.

Reply to this comment

By julie generic (portland)
on August 13th, 2014

this is a fairly fluffy article. most people do not understand the connection between atmospheric rivers and the rocky mountains (all west coast mountain ranges). it’s the atmospheric rivers that bring the precipitation which condenses and manifests as snow and rain when the moisture from them impacts higher geographical locations…mountains.

“Finally, wind and pressure patterns in North America in both years were ideal for steering atmospheric rivers of relatively warm, moist air up along the west coast of Greenland and then over the ice sheet. “These distortions of the jet stream must happen in just the right place to direct atmospheric rivers toward Greenland,” Neff said. “That may be one reason extreme melt events there have been relatively rare.”

Neff and his colleagues found intriguing evidence that a fourth factor—soot from intense U.S. wildfires swept up toward Greenland and deposited on the snow—may have played a role in 1889. Other researchers have found significant deposits of soot in ice core records from the summer of 1889; when darkened by soot or “black carbon,” snow and ice can melt faster. In 1889, Major John Wesley Powell, then director of the U.S. Geological Survey, traveled by train through the northern Rockies during the fire season and later reported to Congress, “The fires in the mountains created such a smoke that the whole country was enveloped by it and hidden from view.”

“Better understanding how factors that can occur naturally, such as long-term droughts or short-term atmospheric rivers, combine to produce an extreme event, such as Greenland’s melt, can help researchers better explain and forecast these events,” said co-author Gilbert Compo, a CIRES scientist working at ESRL. “This is especially important because we expect climate change to continue to warm the oceans and warm and moisten the atmosphere, raising the possibility of more frequent melt episodes.”
- See more at: http://www.colorado.edu/news/releases/2014/04/24/cu-boulder-researchers-find-common-factors-behind-greenland-melt-episodes#sthash.0bYXZpZu.dpuf

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