\nClimatologists call drought a \u201ccreeping disaster\u201d because its effects are not felt at once. Others compare drought to a python, which slowly and inexorably squeezes its prey to death.
\nThe great aridification of 2011 began last fall; now temperatures in many states have spiked to more than 100 degrees for days at a stretch. A high pressure system has stalled over the middle of the country, blocking cool air from the north. Texas and New Mexico are drier than in any year on record.
\nThe deadly heat led to 138 deaths last year, more than hurricanes, tornadoes or floods, and it turns brush to tinder that is vulnerable to lightning strikes and human carelessness. Already this year, some 40,000 wildfires have torched over 5.8 million acres nationwide \u2014 and the deep heat of August is likely to make conditions worse before they get better.
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\nClimatologists disagree about what caused this remarkable dry-out. But there is little disagreement about the severity of the drought \u2014 or its long-term implications. When I asked Richard Seager, who analyzed historical records and climate model projections for the Southwest for the Lamont-Doherty Earth Observatory at Columbia University, if a perpetual drought was possible there, he replied: \u201cYou can\u2019t really call it a drought because that implies a temporary change. The models show a progressive aridification. You don\u2019t say, \u2018The Sahara is in drought.\u2019 It\u2019s a desert. If the models are right, then the Southwest will face a permanent drying out.\u201d
\nGrowing population has increased the burden on our water supply. There are more people on earth than ever, and in many places we are using water at unsustainable rates. Cultural shifts contribute to subtle, far-reaching effects on water supplies. In 2008, for the first time, more people lived in cities than in rural communities worldwide, and water is becoming urbanized. Yet some of the world\u2019s biggest cities \u2014 Melbourne, Australia; Barcelona, Spain; and Mexico City \u2014 have already suffered drought emergencies. Further drying could lead to new kinds of disasters. Consider Perth, Australia: its population has surpassed 1.7 million while precipitation has decreased. City planners worry that unless drastic action is taken, Perth could become the world\u2019s first \u201cghost city\u201d \u2014 a modern metropolis abandoned for lack of water.
\nSimilar fates may await America\u2019s booming desert cities: Las Vegas, Phoenix or Los Angeles.
\nOur traditional response to desiccation has been to build hydro-infrastructure \u2014 dams, pipelines, aqueducts, levees. Many advocate building even bigger dams and ambitious plumbing projects including one that calls for \u201cflipping the Mississippi,\u201d a scheme to capture Mississippi floodwater and pipe it to the parched West. But it is now widely believed that large water diversion projects are expensive, inefficient and environmentally destructive.
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\nThe Holy Grail of water managers is to find a drought-proof water source. Weather modification (\u201cweather mod\u201d), or cloud seeding, is a particularly appealing ideal. When American chemists discovered that dry ice dropped into clouds produced snow, and that clouds seeded with silver iodide produced rain, they rhapsodized about ending drought. Under perfect conditions, weather mod can increase precipitation by 10 to 15 percent. Ski areas, including Vail, Colo., hire companies to seed snow-producing clouds. And China claims that it produced 36 billion metric tons of rain a year between 1999 and 2006.
\nBut critics, including the National Research Council, question weather mod and its efficacy. Bottom line: though evidence suggests weather mod works to a limited extent, it is unlikely to produce a major supply of water soon.
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