No Water, No Life

Water, heat, and soil in ancient and modern desert cities

The desert is alive before the sun rises.  In the faint gray light, a jackrabbit grazes quickly on creosote leaves, knowing it must retreat before the heat arrives.  Its ears twitch at every rustle, but hunger drives it until the first orange edge of daylight touches the ground.  Then it slips back into the shadow of a mesquite thicket.

By midmorning, most creatures vanish underground.  A Gila monster lumbers from its burrow, tongue flicking for the faint scent of a quail nest.  It feeds rarely, but heavily, then disappears again into the earth. Ants pour from their mounds, moving frantically before the soil turns scorching.

At noon, the desert stills.  The saguaros stand silent, storing water they sucked up months ago behind pleated skin. Lizards flatten themselves against shaded rocks, conserving moisture, their movements reduced to the smallest flicks of the tongue.  Even the air seems to stop, as if nothing dares stir beneath the sun’s harsh rays, as the mercury hits 115°F in what little shade exists.  High above, a turkey vulture rides rising thermals, searching for what the heat will claim.

As the sun drops towards the western horizon, a rattlesnake slides from beneath a rock when it becomes cool enough to hunt.  The jackrabbit emerges once more, cautious, moving quickly to feed while the ground begins to release its stored heat.  The kangaroo rat has adapted to survive without drinking by using only the moisture from its own metabolism.

The Sonoran summer is not a place for feeble creatures or those who haven't adapted to the scorching temperatures and parched land.  Yet just down the hill from where this scene unfolds is a metropolis of 4.9 million humans.  Phoenix, and other desert cities, struggle against the hostile environment and seem to defy better judgment.

Why have humans decided to build cities in deserts?

Deserts are characterized by arid environments where evaporation exceeds precipitation, resulting in low moisture and sparse vegetation.  They receive less than 10 inches of rain per year, and often have hot summers, though not always.  Despite these difficult living conditions, many large desert cities have sprung up throughout the ages.  Humans often built in deserts because they were strategic locations as trade routes, valuable resource hubs, or pilgrimage sites.

Settlements like Ur and Uruk in Mesopotamia, Petra in Jordan, and Palmyra in Syria rose in arid lands because they controlled caravan paths, fertile floodplains, or scarce oases.  But deserts never made city life easy.  To survive, people had to solve three constant challenges: water, heat, and soil.

Each city had its own technologies and practices for addressing these issues.  They could get water from rivers or aquifers.  They could capture scarce rains by shaping the earth and controlling the flow of runoff.  They moved and stored water through innovations such as canals, cisterns, and qanats (underground aqueducts).

Relentless heat demanded architecture that protected people from the drastic temperature swings.  Without moisture in the air to regulate temperatures, deserts can experience intense heat in the day and chilling cold at night.  Good building design could help buffer temperatures and make the place inhabitable.  Thick adobe walls, shaded courtyards, and windcatchers that funneled breezes were integral.

Ancient desert cities survived scorching summers by using clever building techniques that worked with nature rather than against it.  The most important idea was thermal mass. Thick walls of adobe or stone absorbed heat slowly during the day and released it at night, keeping indoor spaces cooler when the sun was high and warmer after dark.  Tall ceilings and ventilation openings allowed hot air to rise, so higher roofs and vents allowed it to escape while cooler air stayed lower where people lived.  Many homes and palaces included courtyards with trees, shade, and fountains, which created microclimates.  Evaporation from water features and transpiration from plants cooled the air, while shaded walls reduced direct heat gain.

In places like Iran, windcatchers (badgirs) acted like natural air conditioners, funneling breezes down into rooms and venting hot air out.  Mashrabiya screens in North Africa and the Middle East filtered harsh sunlight, allowing airflow while blocking solar heat gain.  Underground spaces also offered relief.  Cellars, basements, and whole subterranean homes, like the troglodyte houses of Matmata in Tunisia or kivas of the Ancestral Puebloans, used the thermal heat capacity of the dirt.  Earth stays at a more stable temperature, so even when the surface scorched, underground rooms remained cool.

Some desert cites arose because of the rich soils deposited from rivers, while others had poor soils that required terracing, irrigation, and patient cultivation to coax food from the land.  Different cultures had their unique approaches to managing water, heat, and soil, depending on the local environment.  These solutions allowed cities to exist and flourish for centuries.  Yet their survival always hung in a fragile balance.  When water systems failed or soils degraded, even the most powerful desert cities withered.

Cities of the Past

Ur and Uruk were two of the earliest and most influential cities of Mesopotamia, built in the arid plains of southern Iraq more than 5,000 years ago.  Both sat in a desert landscape that depended entirely on the life-giving waters of the Tigris and Euphrates rivers.  Uruk, often called the world’s first true city, emerged around 4000 BC and by 3000 BC may have housed tens of thousands of people.  It created monumental temples, writing on clay tablets, and complex irrigation canals that transformed barren land into farmland.  However, irrigation also brought long-term problems.  The very systems that gave rise to the city began to threaten it, as salts accumulated in the soil.  Agriculture was gradually undermined.

Ur, which rose to prominence later, became a major religious and political center.  It was famed for its ziggurat dedicated to the moon god Nanna and for its wealth as a hub of trade connecting the Persian Gulf to the wider world.  Like Uruk, Ur thrived on irrigation-based farming and organized labor, transforming the desert into a productive agricultural area that fed its people.  But the same heavy reliance on irrigation and delicate river management that birthed them also left them vulnerable.  As soils salinized and river flows changed, their vitality waned.  Still, Ur and Uruk set the model for desert urbanism: cities sustained by ingenuity against harsh conditions.

Petra, carved into the sandstone cliffs of southern Jordan, was the capital of the Nabataean kingdom and one of the most remarkable desert cities of the ancient world.  Founded around the 4th century BC, it flourished as a hub for caravan trade linking Arabia, the Levant, and the Mediterranean.  At first glance, Petra’s location in a rugged, arid valley seems inhospitable, but the Nabataeans mastered the desert’s challenges of water, heat, and soil.  They engineered an elaborate system of cisterns, channels, and covered aqueducts to capture flash floods and store rainwater.  These innovations created reliable reserves that supported both residents and traveling merchants.  To cope with the intense heat, Petra’s architecture took advantage of the natural cliffs.  Monumental facades were cut directly into rock, providing thermal control and protection against the desert sun and cooler interiors for storage and ritual use.  The rocky soil around Petra was not fertile, so the Nabataeans used terracing and runoff farming on the valley’s margins to grow limited crops, supplementing their needs with trade.  At its height, Petra was a dazzling oasis of stone and ingenuity, proving that even in one of the harshest deserts, careful management of nature could sustain a thriving city.

But in the 2nd century AD, the Roman Empire annexed the Nabataean kingdom and redirected caravan trade to new routes that bypassed Petra.  With fewer merchants passing through, the city’s role as a commercial crossroads declined.  In addition, several earthquakes between the 4th and 6th centuries damaged Petra’s water management systems and facades.  Without continuous maintenance, the sophisticated cisterns, aqueducts, and terraces that made Petra habitable began to fail.  As trade declined and agriculture faltered, Petra’s population dwindled.

The Garamantian civilization flourished in the central Sahara, in what is now southwest Libya, between about 500 BC and 500 AD. The Garamantes people overcame their desert challenges by building one of the ancient world’s most remarkable water systems.  They engineered foggara tunnels—underground channels similar to Persian qanats—that tapped fossil groundwater from beneath the desert and carried it for miles to irrigate fields.  These underground aqueducts protected precious water from evaporation, enabling date palms, grains, and other crops to grow in otherwise parched soil.  To manage extreme heat, many structures were built with thick mudbrick walls that moderated indoor temperatures, while the city itself clustered around oasis greenery that softened the intense heat.  The sandy soils were not naturally fertile, but irrigation and careful layering with organic matter allowed sustained agriculture.  Garama, the capital city, became a thriving center of trans-Saharan trade, dealing in gold, salt, and slaves.  However, as their fossil aquifers dried up, so did the Garmantian civilization, leaving only ruins.

Chaco Canyon, located in the high xeric scrubland of northwestern New Mexico, was one of the most extraordinary centers of ancient North America.  Between 850 and 1150 AD, the Ancestral Puebloans transformed this remote high desert into a ceremonial and administrative hub for a vast regional network.  The canyon sits over 6,000 feet above sea level, receives less than nine inches of rain annually, and endures extremes of summer heat and winter cold. Yet here the Chacoans built what are called "great houses"—multi-story complexes of stone and timber, some with hundreds of rooms, kivas for ceremonies, and plazas for gatherings.  These buildings required millions of sandstone blocks and thousands of wooden beams hauled from forests many miles away.

Because rainfall in the canyon was so limited and soils were poor, Chacoans used check dams, diversion channels, and waffle gardens (small grid-like planting plots that trapped water and soil) to conserve moisture.  Archaeological and botanical evidence shows they grew the “Three Sisters” crops—maize (corn), beans, and squash.  Even so, agriculture in the canyon itself was risky, and many scholars believe Chaco imported significant amounts of maize from more fertile surrounding valleys.  Storage rooms in great houses held surplus and imported food.

To handle extreme heat and cold, they used thick masonry walls that absorbed solar energy by day and released it slowly at night.  Underground ceremonial chambers, or kivas, provided cooler spaces in summer and warmer ones in winter.

A kiva, underground space used to escape the heat

Chaco’s influence spread through a system of roads and outlier settlements stretching across the Four Corners region.  Its great houses aligned with solar and lunar cycles, suggesting that astronomy, ritual, and governance converged in the canyon.  But a fifty-year drought started in 1130, which forced Chacoans to emigrate.  Populations declined, and by 1300 the canyon was largely abandoned.  Today, Chaco Culture National Historical Park preserves its ruins as a UNESCO World Heritage Site.

The story told by Chaco Canyon echos those of Petra, the Garmantian and Mesopotamian cities, and other desert cities of old.  Humans created a thriving center of life, trade, and ceremony in the desert by solving the challenges of water, heat, and soil.  Then, when the water goes away, either by humans draining the river or aquifer or by climate change, the people are forced to abandon their homes and move elsewhere.  In the desert, water is life.  No water, no life.

Desert Cities Today

Modern man seems to have transcended the rudimentary techniques of water, heat, and soil management of past civilizations.  We've made incredible progress in these areas that our forbears could not have achieved in their day.  To deal with the challenges of water, heat, and soil today, desert cities rely on three modern technologies: air conditioning, water infrastructure, and global trade and transport.

In 1902, Willis Carrier designed a system to control temperature and humidity for a printing plant in New York. Using coils cooled by compressed air to regulate indoor climates, his invention set the stage for modern vapor-compression refrigeration systems that we universally use in air conditioning to this day.  Without this, we would not be able to freeze or refrigerate food or cool our homes and buildings.  By decoupling our indoor environment from nature's extreme heat, air conditioning became one of the pivotal technologies that make desert cities possible today.  Now, air conditioning systems work essentially the same way all over the world.  Just add electricity and let them hum away—no clever design needed.

The next challenge for modern desert cities such as Dubai, Riyadh, Las Vegas, and Phoenix is that of soil.  Fertile soil is needed to grow food to feed the city's people.  These modern cities have skirted this problem with global trade and transport.  They simply buy food grown somewhere else in the world and have it shipped in. Simple. And it's made possible largely by air conditioning.

The final technology, water infrastructure, varies in a few aspects depending on the particulars of the place, so we'll look at a few examples of cities today.

Dubai sits in one of the driest regions on Earth, receiving less than four inches of rain annually, yet it supports over three million people and some of the world’s most extravagant developments.  The city meets its water demand primarily through desalination, which converts seawater from the Persian Gulf into freshwater.  90% of Dubai’s water comes from desalination plants.  The remainder comes from aquifers that the UAE attempts to refill with more than 7 dams.

The city consumes over 550 liters (145 gallons) per person per day, more than double the global average.  Even ignoring the wider urban metro area, that equates to 1.7 billion liters (450 million gallons) of water every day for Dubai city proper.  This reliance comes at a steep energy cost.  Thermal desalination plants, which boil seawater and condense the vapor, and reverse osmosis desalination systems together account for a significant share of the UAE’s fossil fuel consumption.  It takes 3-5 kilowatt-hours of electricity per cubic meter of water (which is 11-19 Wh/gallon).  That works out to about 7 gigawatt hours per day, or 2.5 terawatt hours per year, making it both expensive and carbon-intensive.  Despite investments in solar power and efficiency measures, Dubai’s water remains inseparable from energy, meaning its survival in the desert depends on a continuous flow of fuel to keep the taps running.

Riyadh, the capital of Saudi Arabia, with 8 million people, draws its water primarily from desalination plants and groundwater wells.  In 2020, two major desalination plants supplied about 62% of the total water used in the city.  The remaining 38% comes from nine significant groundwater wells within the Riyadh area.  There has been a major expansion of seawater desalination capacity in recent years, likely because leaders know the precarious situation of groundwater reserves.  Now, Saudi Arabia desalinates over 8 billion liters (2.1 billion gallons) per day, accounting for more than 90% of the country’s water consumption.  By 2030, desalination capacity in Middle Eastern countries is expected to almost double.  Energy is not the only cost to water desalination.  The super-salty brine that gets discharged back into the ocean can disrupt ecosystems by killing off local marine life, the downstream consequences of which are not fully known.

Here in the United States, landlocked Sin City doesn't have the luxury of desalination.  Las Vegas gets about 90% of its water from Lake Mead, the reservoir on the Colorado River created by the Hoover Dam's completion in 1936.  The rest comes from local groundwater wells and treated or recycled water.  But Vegas faces a growing crisis.  Lake Mead’s water level has dropped more than 150 feet since 2000 due to long-term drought and declining snowmelt in the Colorado Basin.  Because much of the city's supply rests on Colorado River allocations shared among multiple states, lower water levels trigger mandatory supply cuts.

Las Vegas has responded with conservation measures: replacing lawns with desert landscaping, restricting watering schedules, offering rebates for reducing outdoor water use, and implementing infrastructure programs to limit waste.  In the 1990s, the region averaged about 350 gallons per person per day (GPCD).  Today, per-capita use has declined to less than 220 GPCD under the Southern Nevada Water Authority’s conservation programs.  The SNWA has set a goal to reduce per-person daily water use even further, aiming for 86 gallons per person per day by 2035.  That 37% decrease in per-capita water use from 1990 to 2025 seems like a win.  The city has been one of the best examples of a large-scale coordination to cut water usage, but still, it's running out of water.  Why?

In 1990, the Las Vegas metro area had around 700,000 people.  Today it has over 3 million—428% of what it was.  So, despite each person using 37% less water in the last 35 years, water consumption overall has increased by a factor of 2.7.  This increase in water use, combined with decreased flows from the Colorado River, caused by climatic changes, puts Vegas in a hot, dry, precarious place—with Lake Mead's growing bathtub ring providing a reminder.

The Hoover Dam and Lake Mead, a bathtub ring showing were the water once was

As we conclude our tour of desert cities, we return to that sun-scorched metropolis in the Sonoran Desert, whose environment we painted a scene of in the beginning.  Phoenix rose from the ashes of a Native American culture called the Hohokam that inhabited the same land from about 300 to 1450 AD.  The Hohokam dug 1000 miles of canals to divert water from the Salt and Gila Rivers, transforming desert land into productive fields to feed their people.  These canals, some over 60 feet wide and 10 feet deep, supported large-scale agriculture of maize, beans, squash, and cotton, allowing sizable communities to flourish in an otherwise arid environment.  By the 1400s, the Hohokam culture declined, likely due to prolonged droughts followed by flooding that damaged canals, salinization of the soil, over-hunting of native animals, and the eventual breakdown of the social order.  The very name “Hohokam” comes from the term Huhu-kam, meaning “all used up.”

In his book, A Brief History of Phoenix, John Talton describes how John "Jack" William Swilling, the man most responsible for founding Phoenix, got a group of men together in December of 1867 and started clearing out some of the prehistoric canals of the Hohokam.  Phoenix was incorporated in 1881.  Despite the extreme summer heat, Phoenix lies in one of the great alluvial valleys of the world.  Four rivers converged in the Salt River Valley, draining a watershed of 13,000 square miles fed by mountain snowmelt.  By 1890, 125,000 acres were under cultivation, growing wheat, beans, corn, sweet potatoes, grapes, sugar cane, citrus, dates, figs, and other vegetables and fruits.

In 1887, a branch of the Southern Pacific Railroad arrived, followed by the Santa Fe Railway in 1895. The railroads allowed people to export produce, and they promoted the young city's growth potential to capitalists back East.  Settlers were in part attracted by the Desert Land Act of 1877, an expansion of the Homestead Act, which allowed settlers to buy 640 acres for $1.25 an acre if they could irrigate them.  Teddy Roosevelt signed the Newlands Reclamation Act in 1902, which was a federal law that funded irrigation projects in the arid American West by using money from public land sales to create fertile farmland.  The act established the U.S. Reclamation Service (now the Bureau of Reclamation) and led to the construction of major dams, canals, and reservoirs.

Theodore Roosevelt Dam

The first major dam for Phoenix was the Theodore Roosevelt Dam on the Salt River, completed in 1911.  Between that dam and Phoenix, the Mormon Flat Dam (1925), the Horse Mesa Dam (1927), and the Stewart Mountain Dam (1930) followed.  Then the Verde River was controlled with the Bartlett Dam (1939) and the Horseshoe Dam (1946).  A series of canals and a diversion dam allow delivery of water from the Salt and Verde Rivers into the city and agricultural zones.  Over time, Phoenix’s water supply became highly engineered.

By the mid-20th century, Phoenix had tapped all of its possible water sources.  That is, with the exception of the Colorado River.  After repeated lawsuits with California over that water, in 1968, President Lyndon Johnson authorized the $4 billion construction of the last great reclamation project, and one of the most incredible feats of civil engineering in history.  The Central Arizona Project (CAP) took water from the Colorado River at Lake Havasu, pumped it over a mountain range into a 336-mile canal, and lifted the water nearly 3,000 vertical feet to distribute it to Phoenix and Tucson.  When it was completed in 1993 after 20 years of construction, the CAP fueled the city's growth machine of hyper-expansion with more water.  An influx of developers bought out the farmers in the Salt River Valley to pave it over with subdivisions, and centuries-old saguaros and Hohokam ruins were destroyed without oversight or remorse.

Today, about 58% of Phoenix's water supply comes from the Salt and Verde Rivers via the Salt River Project (SRP), about 40% comes from the Colorado River, delivered through the Central Arizona Project (CAP), and the remainder (~2%) is from groundwater.  It's hard to pinpoint exact figures for annual usage because of different water providers and blurry boundary lines, but the Phoenix metro area uses about 2.3 million acre feet, or 750 billion gallons, of water annually.  That's over 1 million Olympic-sized swimming pools. Of that, about 35% is for city and municipal use, about 50% for domestic and outdoor use, and about 40% is for agriculture.  The average Phoenix resident uses 155 gallons per day.  Since Phoenix's local aquifers are “fossil” and replenish very slowly, if at all, pumping from them is unsustainable. That water is viewed as emergency water.  Much of Phoenix's groundwater has been polluted by twentieth-century industry.  It's home to 12 EPA Superfund sites.

Phoenix is investing in water conservation because it sees the fragility of its situation.  The population is rising (now at 4.9 million for the metro area), and the flow of the rivers that it depends on is variable and, on average, declining.  Not just Phoenix, but many cities in the Western US are dependent on the diminishing flow of the Colorado River.  In the last 100 years, the river's average flow has declined by 30%. To make matters worse, damming rivers creates reservoirs that water readily evaporates from.  The Bureau of Reclamation estimates that about 1 million acre-feet per year evaporates from Lake Powell and Lake Mead alone.  A broader water budget study reports that about 11% of all water consumed in the Colorado River Basin is lost through evaporation from reservoirs.

What can we learn?

We've seen how desert cities in the past have used low-energy design to control water, heat, and soil.  They were able to thrive for centuries until the water dried up.  Whether by self-inflicted over-extraction or by inevitable changes in climate, water shortages ultimately spelled the end.  No water, no life.

We've also seen how modern cities manage water, heat, and soil.  The difference today is that our advanced technology seemingly allows us to bend nature to our will.  The population of desert cities grows to the maximum size that the water will allow—in good times. Then, when there's drought, we dam rivers and pump them hundreds of miles over mountains, creating the transient illusion of more water.  The cities of the past we discussed had thousands to tens of thousands of people. Today's desert cities have millions.

We have access to several orders of magnitude more energy than any civilization of the past. We use it to move refrigerated food, desalinate seawater, and air-condition glass skyscrapers that act like giant heat-trapping greenhouses. Abundant cheap energy is a luxury that obviates good design.

Desert cities are growing, and growing fast. It would be wonderful if they could avoid the disasters of their fallen predecessors.  But even modern cities need water.  And as they grow, they require more water.  Coastal desert cities may be able to desalinate the seas with cheap energy reserves, for a while, but landlocked cities don't have that option.  The sources of water they depend upon have hard limits.  And we must consider that the climate changes, both naturally and from human activity. The latter is not helping desert cities.  That means having the discipline to limit use of the available water in average times so we'll have the resilience when drought inevitably arrives.  Drilling wells is not a strategy; it's a deeper straw contest that drains aquifers and hurts us all.  If we don't learn to live within the limits of what the rivers provide, cities like Phoenix may suffer the same Ozymandian fate as the Hohokam that preceded it.  Two cities of the same place and the same fate, separated by time.

It's not just Phoenix at risk.  It's Las Vegas, Tucson, Los Angeles, San Diego, Salt Lake City, Denver, St. George, Mexicali, and countless others.

We must protect our rivers and aquifers.  And maybe, just maybe, if we can bear it, preserve some of that precious flow for nature and the countless species that depend on it.

No water, no life.

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