Our Water Problems Are a Crisis of Management
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The concern to ensure a steady water supply was pervasive throughout South Asia in his time. Thousands of small dams created cascades of connected lakes (locally called "tanks") that made irrigation possible all year round, despite the vagaries of the monsoon climate. Comparable inventiveness produced aqueducts in Rome, elaborate systems of underground tunnels ( qanats) in the Middle East and Northern Africa, and King Nebuchadnezzar II's irrigation systems for the hanging gardens of Babylon. The Babylonian irrigation worked, but Mesopotamian society apparently failed to control the slow build-up of salt in the soil, faced a water crisis, and ultimately collapsed.
Salinization remains a serious threat to irrigated lands, but we are now hearing warnings about something much more dangerous: a genuinely global scarcity of water. Reports describe majestic rivers such as the Yellow River in China no longer reaching the sea. Ships sit on the dry bed of the Aral Sea. Droughts such as those that have ravaged the Australian countryside in recent years appear to be increasing in frequency and severity. In 2006 the International Water Management Institute, which I directed at the time, reported that water scarcity affected a full third of world population. In 2007 the Intergovernmental Panel on Climate Change predicted that, due to climate change, the number of people facing water scarcity would grow. Others, too, say that there is a global water crisis, the availability of water is dwindling, the world is running out of water, water is the blue gold, and that future wars will be fought over water. In When the Rivers Run Dry (2006), Fred Pearce characterizes this emerging shortage as the defining crisis of the twenty-first century.
So, is the planet drying up? Not exactly, but a growing number of people are sharing a fixed amount of water, and that water is badly managed and increasingly polluted. Thanks largely to unsafe drinking water, more than 2 million children die of diarrhea each year. Six hundred million subsistence farmers lack irrigation water and are mired in poverty. Wetlands have been decimated in Europe, North America, and Asia, and fish populations are collapsing. Drought caused a more than 50 percent drop in Australia's wheat production in 2007 and sparked a ten-year peak in global wheat prices. Burgeoning African and Asian cities, from Dakar to Beijing, face severe water shortages. Water rationing in these cities, to several hours per day or several days per week, is the norm rather than the exception.
We can avoid a full-blown global disaster. Unfortunately, the water crisis is complicated, often misunderstood, rarely grasped holistically, accelerated by climate change that melts glaciers and icecaps, and exacerbated by biofuel expansion that further stresses scarce water supplies. Forestalling it will require a mix of sustained technological innovation and institutional reform, all guided by deeper understanding and some new thinking.
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Most of the earth's water is saline, located in seas and oceans. And most of the earth's fresh water is locked up in the ice caps around the poles. The rest is the water pumped around by the sun in the hydrological cycle: water that evaporates into the atmosphere, gathers in clouds, and falls as rain.
Every year roughly 100,000 cubic kilometers of rain fall on earth -- some 15,000 cubic meters per person per annum. Because the quantity of solar energy that reaches earth is more or less constant, the total amount of water that evaporates also is more or less constant. Population, however, is not constant. It has doubled in the last fifty years, resulting in a 50 percent decline in water availability per person. Climate change may alter that equation somewhat as glaciers and ice caps melt, but it is expected to have much larger impact on the seasonal distribution of rainfall -- dry periods will get drier, wet periods will get wetter, floods and droughts will worsen -- than on the total amount of water available.