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Water for all

Speed read
  • The Colorado River Basin provides water to 40 million Americans across nine states
  • Climate change will likely reduce the amount of available water
  • Advanced hydrological models provide detailed information about future scenarios

You have something in your house that our ancestors could only dream about. You use it every day, and it provides you with one of the necessities of life through the simple flick of your wrist.

This device, of course, is your faucet.

<strong>The Colorado River Basin</strong> is located in the southwestern US. High-resolution satellite data of land cover is used by the HPC model to estimate surface interactions with the atmosphere. Courtesy Kristen Whitney. Our water distribution systems are so advanced, it’s easy to forget that our water doesn’t magically appear from the tap. It has to come from somewhere, and for Americans living in the Southwest, that deposit of H2O goodness is called the Colorado River Basin

Covering portions of Wyoming, Colorado, New Mexico, Utah, Arizona, and beyond, the Colorado River Basin supplies water to 40 million Americans and irrigates roughly 5.5 million acres of agricultural land. Unfortunately, as is with many important Earth systems, this basin will be affected by climate change. 

Studying such an extensive water network is only possible with the help of high-performance computing (HPC). To get a better understanding of what the future holds for this vital resource, Kristen Whitney and Enrique Vivoni of Arizona State University (ASU) took a deep dive into the data.

A drier future

Although it’s impossible to perfectly predict the future, many regional climate models forecast a reduction in the amount of available water. Vivoni, a professor at ASU and Whitney’s PhD supervisor, wonders about the consequences of climate change.

“Greenhouse gas emissions are changing precipitation patterns and temperature records, and that worries water managers,” says Vivoni. “They want to know if they can reliably provide the same water supply that they have throughout the 20th century under the 21st century climate. That's the big question.”

<strong>Reductions in stream flow.</strong> The Colorado River Basin supplies irrigation water for nearly 4.5 million acres of land. Courtesy Central Arizona Project. But knowing that water availability will change is not enough. It’s important to have a more granular understanding of the details of the coming transformation–the when and where and how much.  

Whitney’s study turned to HPC modeling to examine those details more closely. She looked into what happens to stream flow under different scenarios for future emissions of pollutants. What’s surprising is that the news isn’t all bad. 

“Basin-wide, we're seeing reductions in stream flow,” says Whitney. “All the scenarios are showing some level of reduction. But what's interesting is when you look at the different sub-basin scales. Particularly at seasonal scales rather than just annual, some basins are showing either little to no decrease. There may also be some increases, particularly in the winter season in some of the upper basin regions.” 

As Whitney points out, the Colorado River Basin covers a lot of territory. It includes around 246,000 square miles across 7 states and parts of Mexico. The geography of such a large area varies wildly. Climate change won’t affect it all equally, which is why it was so vital to rely on powerful supercomputers for the modeling.

The world is not flat

Hydrological models are data-intensive, incorporating earth-observation data from satellites, aircraft, and field instruments. They run at very high resolutions, from 1 meter by 1 meter up to 10km by 10km. Vivoni and Whitney used over 800,000 CPU hours on the Agave computing cluster at ASU. 

“Without high-performance computing clusters, we couldn’t do the intensive, high-resolution modeling that we do. We couldn’t run long-term scenarios,” says Vivoni. 

<strong>Many existing hydrological models</strong> treat land surfaces as if they’re flat. But important geographical features in the Colorado River Basin could drastically affect water flow. Shown: The Colorado River at Horseshoe Bend in the Grand Canyon National Park. Courtesy Central Arizona Project.And when it comes to water flow, topography matters. Yet many existing hydrological models treat land surfaces as if they’re flat. That ignores important geographical features in the Colorado River Basin that could drastically affect water flow. 

“We're now adding the mountains back into the hydrology model, adding the right type of vegetation and the right type of soil,” says Vivoni. 

The researchers want to understand how different sub-basins might respond to different climate change and land use scenarios in the future

“I'm using a large-scale hydrology model that's run at resolutions from the six kilometer by six kilometer scale,” says Whitney. “We use the HPC cluster here at ASU because we're creating simulations that extend until the end of the 21st century. We're running hourly resolutions, and we're assessing results under eight different climate model packages, as well as running each climate model under both low and high emissions scenarios.”

When dealing with the water supply for millions of people, emotional reactions can run high. But Whitney cautions against blind fear, instead opting for informed action. 

“I get a lot of questions from people, like ‘When are we going to run out?’” says Whitney. “People are scared, I think, because they don't really know the true story. I think it needs to be talked about more, not only in our media but on a regular basis. We need more awareness of where our water comes from, where it goes, and how to best conserve.”

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