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Will Modern Phoenix Outlast the Prehistorical Hohokam?

Casa GrandeDarell Duppa, a late nineteenth century pioneer of the American Southwest, may barely warrant a historical footnote, but he left one memorable legacy: he named the capital city of the state of Arizona.

With a classical education and five languages under his belt, Duppa was no typical Western pioneer.  He drank and gambled, to be sure, but he also read Roman and Greek classics in their original languages.  Born in France, he later headed to America and eventually landed in central Arizona.
 
When it came time to name the new settlement that had grown up along the Salt River, Duppa drew on his knowledge of ancient mythology and chimed in that Phoenix, the mythical sacred firebird that rises anew from its own ashes, would be the perfect name.
 
“Prehistoric cities, now in ruins, are all around you; a prehistoric civilization existed in this valley.  Let the new city arise from the ashes of those ruins,” he proclaimed.
The civilization Duppa was referring to was the Hohokam, a remarkable people who lived in the valleys of the Salt, Gila, Verde, Santa Cruz and San Pedro rivers of south-central Arizona for a thousand years, from 450 to 1450.
 
The Hohokam formed one of the earliest and greatest irrigation societies of the Western world.  In the lower Salt River valley, the site of modern Phoenix, the Hohokam built canal networks spanning 300 miles in aggregate length. They turned some 70,000 acres of desert into flourishing fields of beans, corn, squash, and cotton.  Villages sprung up about every three miles along the major canals, each covering about 15 square miles and cultivating some 2,400 acres.
 
The productivity of this irrigation civilization yielded food surpluses that freed up time for other endeavors.   Many villages took pride in their ball court, a large oval depression where villagers gathered to enjoy games and public events. The artistically gifted crafted distinctive red-on-buff pottery, as well as beads, bracelets, painted shell ornaments, and beautiful ceramics.  With the Chaco people to the north, they exchanged cotton for turquoise.
 
In short, the Hohokam boasted impressive engineers, builders, artists, irrigators, farmers, athletes, entrepreneurs, and traders – and they built a civilization that weathered a millennium.
 
As I explored the ruins of the Hohokam on a recent trip to central Arizona, one question kept popping into my mind:  will modern Phoenix thrive as long as the Hohokam did in these desert environs?
 
I had pondered this question before, when a study published in late 2010 found that the mega-drought in the Southwest that lasted two decades during the middle of the 12th century, and that almost certainly contributed to the Hohokam’s demise, could happen again as human-induced greenhouse-warming turns the region’s climate hotter and drier.
 
But standing amidst the ruins of Pueblo Grande, which sits a stone’s throw east of Sky Harbor Airport, and then passing over the bone dry Gila River as I headed out to Casa Grande, a Hohokam ruin southeast of Phoenix, a more fundamental question arose: with or without climate change, will the water supply that supports this vast enterprise hold out for a thousand years, and if so, how?

Crossing the dry Gila River en route to Casa Grande. photo by Sandra Postel
 
About half of the Phoenix water supply comes from the Salt River Project, which employs six dams, 1,300 miles of canals and 255 high-volume wells to capture water from the Verde and Salt River watersheds. These surface supplies are already fully used. Heading north out of Phoenix, I crossed the Salt River and nearly missed it.  This major river, which had serviced the Hohokam for a millennium, was completely dry.
 
Some two-fifths of the capital’s supply comes from the Central Arizona Project (CAP), among the last of the huge federally subsidized Western water projects.  The CAP carries Colorado River water from Lake Havasu on the California-Arizona border 190 miles to Phoenix and an additional 146 miles south to Tucson – a total of 336 miles, and uphill.   At its final point, the CAP canal is 3,000 feet higher in elevation than where it begins.  The CAP is Arizona’s biggest user of electricity.
 
Most of the remaining one-tenth of Phoenix’s water supply comes from underground aquifers that are being depleted. Hydrologists estimate that the Basin and Range aquifers beneath Phoenix and Tucson would last about 400 years at 1980 (pre-CAP) depletion rates.
 
Overlay climate change and prospects for a sustainable water supply get dimmer. In times of shortage, California gets its full allotment of Colorado River water before Arizona gets any. That means the CAP canals could at some point run as dry as the Salt and Gila rivers already have.
 
Of course none of this is news to Arizona or Phoenix water officials.  They are preparing for dry days by banking some CAP water underground. Conservation and recycling are modestly stretching the supply.  And farmers will no doubt continue to sell water to Phoenix and other Arizona cities.
For the Hohokam, the capital and energy needed to acquire their water was as visible as the sweat on their backs. Archeologists estimate it took nearly a million person-days of human labor to construct just the trunk lines of one of the Hohokam’s major canal systems.  That’s equivalent to 2,740 people working seven days a week for a year.  And that’s not counting maintenance and repair.
 
For modern Phoenicians, by contrast, abundant water arrives at their doorsteps cheap enough to irrigate big lawns and fill swimming pools – arguably proof of modern water management’s success.
 
And maybe this is the defining difference between the two cultures’ relationship with water: for the Hohokam, visible costs and the hard reality of water’s limits, while for the Phoenicians, hidden costs and an illusion of plenty.
 
So which culture will win the endurance test?
 
We’ll find out by 3012, at the latest.

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