The World in 2050_ Four Forces Shaping Civilization's Northern Future - Laurence C. Smith [62]
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.
Top Twenty World Port Cities Most Vulnerable to global Sea Level Rise, Hurricanes, and Land Subsidence
(Sources: R.J. Nicholls, OECD, 2008)
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