the Upper Ninth Ward would drown nearly two centuries later.
As delta cities grow and their rivers become oversubscribed or polluted, they start pumping their groundwater resources. Groundwater removal—from what is essentially a pile of wet mud—causes the delta sediments to compact and settle, lowering the delta’s elevation closer to that of the sea. Even in the absence of groundwater pumping, some settling is normal. In a natural system, this settling is compensated by fresh blankets of silt laid down by floods. But the dikes and levees built to protect delta cities also prevent these fresh reinforcements from arriving. Farther upstream, dams thrown across the river snare the delta’s lifeblood of new sediment. Dam operators groan and search their budgets for dredging money. The conveyor belt is cut. Hundreds of miles downstream, the ocean starts taking back the land.
Important delta cities are found all over the world. They face the triple threat of rising oceans, sinking land, and sediment-starved coastlines. Without replenishment their coasts are washing away, bringing ocean wave energy and storm surges ever closer to the sinking cities. When combined with projected trends of rising sea level, population, and economic power, this puts some of the world’s most populous and prosperous places in harm’s way.
The risk assessment study on the next page was recently commissioned by the OECD.263 The study considered all 136 of the world’s major port cities holding one million people or more. As of 2005, about forty million people living in these cities were considered to be living in places at direct risk from flooding. The total economic exposure to flooding—in the form of buildings, utilities, transportation infrastructure, and other long-lived assets—was about USD $3 trillion, or 5% of global GDP.264 Under current trajectories of population growth, economic growth, groundwater extraction, and climate change, by the 2070s the total exposed population is forecast to grow more than threefold, to 150 million people. The economic exposure is forecast to rise more than tenfold, to USD $35 trillion, or 9% of global GDP. Of the top twenty major at-risk cities, exposed human populations could rise 1.2- to 13-fold, and exposed economic assets 4- to 65-fold, by the 2070s. Three-quarters of these major cities—nearly all of them in Asia—are found on deltas. Clearly, we are about to begin paying great attention to a new kind of defense spending. It’s called coastal defense.
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Imagining 2050
The trends I’ve described—rising water demand; oversubscribed and/or polluted water sources; reduced time-delays and free storage from snow and ice; sharper floods and droughts that are also harder to predict and insure against; the competitive marriage of water to energy; and booming port cities on increasingly risky coasts— all stem from our four global forces of demographics, natural resource demand, globalization, and climate change.
Whether for-profit multinational corporations offer the best solution for tackling water quality problems in impoverished countries remains an open question that is heatedly debated. However, global trade flows of “virtual water” embedded in food, energy, and other goods are already smoothing out some stark water inequities around the world. Compared with other irritants, international water disputes have seldom led to war. Continued economic integration could foment even better water management across borders—especially when nudged along by free hydrologic data measured from space and posted openly on the Internet. Finally, the not-so-far-fetched possibility that new international trade flows in water—not just virtual but actual, physical water—could emerge as a partial solution for some water-stressed places that will be explored further in Chapter 9.
Looking ahead to the next forty years, it’s not hard to see where the big pressure points lie. Joseph Alcamo directs a research institute at the University of Kassel dedicated to exploring different possible futures for humanity’s water supply. To do this they built WaterGAP,265 a sophisticated computer model incorporating not only climate change and population projections but also other factors like income, electricity production, water-use efficiency, and others. WaterGAP is thus a powerful tool for simulating a range of possible outcomes depending on the choices we make.
A typical, “middle-of-the road” WaterGAP scenario is shown here for 2050.266 Regardless of how the WaterGAP model parameters are twiddled, the big picture is clear: The areas where human populations will be most water-stressed are the same areas where they are water-stressed now, but worse. From this model and others, we see that by midcentury the Mediterranean, southwestern North America, north and south Africa, the Middle East, central Asia and India, northern China, Australia, Chile, and eastern Brazil will be facing even tougher water-supply challenges than they do today. One model even projects the eventual disappearance of the Jordan River and the Fertile Crescent267—the slow, convulsing death of agriculture in the very cradle of its birth.
Computer models like these aren’t built and run in a vacuum. They are built and tuned using whatever real-world data scientists can get their hands on. Take, for example, the western United States. In Kansas, falling water tables from groundwater mining is already drying up the streams that refill four federal reservoirs; another in Oklahoma is now bone-dry. These past observed trends, together with reasonable expectations of climate change, suggest that over half of the region’s surface water supply will be gone by 2050.268 Kevin Mulligan’s projection of the remaining life of the southern Ogallala Aquifer requires no climate models at all—it simply subtracts how much water we are currently pumping from what’s left in the ground, then counts down the remaining years until the water is gone.
In the United States, the gravest threat of all is to the Colorado River system, the aorta of water and hydropower for twenty-seven million users in seven states and Mexico. It supplies the cities of Los Angeles, Las Vegas, Tucson, and Phoenix. It irrigates over three million acres of highly productive farmland. Global climate models almost unanimously project that human-induced climate change will reduce Colorado River flows by 10%- 30%269 and already, its water is heavily oversubscribed.
More water is legally promised to the Colorado’s various shareholders than actually flows in the river.270 Its left and right ventricles are Lake Mead and Lake Powell, two enormous reservoirs created by the Hoover and Glen Canyon dams, respectively. They haven’t been full since 1999. A bitter combination of high demand, high evaporation, and falling river flows has thrown the Colorado River system into a massive net deficit of nearly one million acre-feet per year, enough water for eight million people. By 2005, Lake Powell was two-thirds empty and almost to “dead pool” (the elevation of its lowest outlet, below which no water can be released by the dam and it ceases to function).271 This desiccation stranded marinas and boat docks on dry land and left a white bathtub ring some ten stories high on Lake Powell’s newly exposed canyon walls. “It was as though in four years . . . Lake Powell had simply vanished,” wrote James Lawrence Powell of his namesake in
I’m glad humanity has a decent track record with things like settling water disputes with courts rather than missiles, and exporting food from the places that have water to the places that don’t: If any of these model forecasts are correct, we’re going to need it. Humans currently withdraw about 3.8 trillion cubic meters of water annually, and are projected to require more than six trillion in the next fifty years. To serve India’s expected 2050 population of 1.6 billion, even with improved water efficiency, will require a near-tripling of its water supply. Farmers, energy utilities, and municipalities are all in competition for water. Put it all together and the numbers don’t add up. Something will have to give.
The survival of California’s thirsty dry cities—like Los Angeles and San Diego—seems all but guaranteed. Their populations and economies are growing briskly. Despite annual sales of over USD $30 billion, California agriculture still contributes less than 3% to the state’s economy—and cities use far less water than irrigated farms. Even with climate changes and a projected 2050 population of about 20 million, there will still be ample water for Angelenos and San Diegans to drink and shower and cook. Ample water for California farmers, however, is far less assured.
Forced to choose, cities will trump agriculture. Farmers will either lose or sell their historic water rights.
