Groundwater pumping is changing surface levels in Phoenix

August 11, 2015

The ground level in portions of the metro Phoenix area is dropping at an annual rate of nearly two centimeters, or almost an inch a year, according to two Arizona State University scientists.

This is caused by the pumping of groundwater from subsurface aquifers, say ASU researchers. Map of changes in surface level in metro Phoenix Satellite-borne radar data from 1992-1996 and 2003-2010 have let ASU graduate student Megan Miller, of the Radar Remote Sensing and Tectonic Geodesy Lab at the School of Earth and Space Exploration, track annual changes in surface level. The computer image shows Valley areas that are rising in red; ones that are dropping in blue. Download Full Image

Apache Junction, at the east end of the Valley, is seeing the fastest drop, followed by Sun City West, Peoria and the north Valley.

Although changes of a few centimeters a year may not seem substantial, when they continue for many years and over long distances they can have serious and expensive impacts. Structures such as the Central Arizona Project (CAP) and other canals, utility lines, water and gas mains, storm drains and sewers are most affected, while office buildings, apartments and homes can also become damaged as ground levels drop.

"Pumping groundwater alters the elevation of the land surface at different rates around the Valley," said ASU researcher Megan Miller. "This happens because the sedimentary basins in the Phoenix metropolitan area vary in thickness and properties."

Miller, a graduate student, and professor Manoochehr Shirzaei, both of the School of Earth and Space Exploration, work with synthetic aperture radar carried on Earth-orbiting spacecraft. Such radar can measure ground elevations to less than an inch over wide areas. By repeating the measurements over time, changes can be detected, tracked and mapped.

The elevation data they used for their study, which has just been published in the Journal of Geophysical Research, come from 1992-1996 and 2003-2010.

"In parts of Chandler, Mesa, and Scottsdale, the ground level has risen in recent years," Miller said. "This is because we are storing the unused part of our water allotment in the ground." But she notes that this cannot be done everywhere, and it cannot undo much of the subsidence that has previously occurred.

"In areas where the land has subsided, the basin layers have become compacted. When water was pumped out, the pore spaces in the aquifers became empty, and the layers settled until the spaces were eliminated," Miller explained.

The water table — the height of the groundwater level — has increased during the period they studied, even where the surface elevation of the land has fallen, Miller said. The continued sinking of the surface is from pumping that occurred years ago.

The demand for water has remained relatively stable during this time, mainly due to the decline of agriculture in the Valley. Miller noted, "As more people have moved here, they have settled on land that previously grew crops, which use more water."

Because residential and industrial areas use less water per acre than agriculture, the population increase has been offset by the decrease in agricultural water use. The net result, Miller said, is that demand held fairly steady during the study period, but the source of demand has changed.

"Eventually," Miller said, if current supply and demand trends continue, "we will no longer have a surplus." Then, she said, "the water table will resume dropping."

Groundwater pumping has two main effects, one short-term, the other long. "The biggest short-term problem is earth fissuring, or cracks that develop and threaten structures and their foundations," Miller said. "Longer term, the changes in surface level can affect where floodwaters go, which could produce huge problems for the Valley."

A second long-term effect occurs, she adds, when groundwater withdrawals continue: The subsidence reduces the aquifer system's capacity to store water.

"We live in a desert, and our underground canteen is getting smaller."

The School of Earth and Space Exploration is a unit of ASU's College of Liberal Arts and Sciences.

Robert Burnham

Science writer, School of Earth and Space Exploration


The man with the power to predict economic success

August 11, 2015

There’s a mild disappointment when you meet Shade Shutters and listen to him discuss his area of study.

Because after you learn he’s a research scientist in ASU’s Global Security Initiative, you really want this man with the comforting demeanor and pleasant eyes to tell you he’s studying the impact of reducing solar gain on communities. Shade Shutters Shade Shutters shows some of the economic analytics he has produced to assist communities in making development decisions, in the Decision Theater in Tempe on July 28. He is a research scientist in ASU’s Global Security Initiative. Download Full Image

After all, his name is Shade Shutters.

Once you get past the absence of typecasting, all disappointment is washed away because what Shutters will tell you is much more interesting than the amusement of an obvious name game.

Like how this former international finance professional went back to school to get a doctorate in biology so he could better understand his field – more on that in a bit. Or how he has developed an algorithm that can divine which industries fit best in a particular city. He can even help a city determine whether it has the right makeup to become a creative or “green” economic hub.

Yes, in a sense, Shutters has created digital clairvoyance for the world’s civic economies.

This is how it works:

Say Happyland, Oklahoma – an actual town, by the way – believes it’s the perfect location for a pharmaceutical industry, but the city leaders want to consult Shutters just to be certain. He’ll collect the city’s metrics, then overlap the data associated with the pharmaceutical industry into his algorithm.

The results will tell him whether Happyland has the appropriate infrastructure, complementary businesses and whatnot to support the decision to woo a pharmaceutical company. It also examines economic impact, risk and other factors.

“So, if you want to shoot to a certain industry and invest some money and raise some bonds and create infrastructure, this is probably a better fit over here,” he says. “That’s the kind of thing they need to help them prioritize their growth strategy.”

If it doesn’t look like a match, Shutters can tell the smiley folks of Happyland which industries would fit best in their burgh. Or, conversely, he could show an industry leader which locale is best suited for their long-term success.

In some ways, this is oversimplifying the detail of Shutters’ methodology, which mines a mind-boggling amount of data that he refines and displays on multiple screens in ASU’s Decision Theater to visualize the overlapping data points. In a more abstract way, what he’s doing is looking at each city as an organism of sorts, how each of its different sectors and traits interact with incoming businesses.

And that’s where his biology background comes into play.

“Think of all the occupations in an urban economy as a network. How are they interlinked and intertwined? They make a web of labor,” says the native of Seymour, Indiana, the same town that birthed rock star John Mellencamp. “What we’re most interested in is what does the big web look like of all occupations?”

And to do that, sometimes it helps to view the city in the same way you view organisms, by looking at which industries work together and rely on each other to maintain the health of the overall ecosystem.

He calls the effect “tightness,” as in how bunched, or tight, a city’s connectivity between jobs and industries is. For instance, a city reliant on the health-care industry would like to have a “tight” network of jobs that complement each other.

And in studying the tightness of cities, Shutters discovered something rather interesting.

“The prevailing theory out there is that these really tight, integrated, highly interdependent systems are the most resilient. … And, instead, what I found was the opposite,” he says. “It’s those tightly wound cities that had a huge drop in economic performance during the recession.”

The little cities? They fared much better. He attributes it to the smaller cities being composed of industries that don’t rely on complementary parts to survive.

“Like a human body, if you get shot, it might only affect you right here (pointing to his shoulder), physically, but the person is probably going to die because the whole system collapses,” Shutters says. “Whereas you take an animal like the sponge, you can run them through a sieve and they re-form. They’re not tightly integrated like a human body.”

And that’s where the biological perspective helps his cause so well.

But though the methodology and implementation for his algorithm are very cool, it’s missing one key feature: a name.

So far, Shutters says he and the other co-creators, ASU’s Jose Lobo and former ASU Sustainability Scientist Rachata “Chot” Muneepeerakul, have been calling it “Urban Science Working Group.”

Not as unique or interesting as, say, Shade Shutters. But it’s still early. The theory of this project was presented just two years ago, with the practical applications being implemented only recently.

It’s going to grow and develop — just don’t expect it to languish in scholarly journals or live at academic conferences.

“I’m really interested in implementing change with decision makers,” Shutters says in his office. “I don’t want to just publish and move on.”