I’ve often thought of the Tonle Sap catchment area of the Mekong River as the Liver of Asia. The Tonle Sap, for those who don’t already know, is the name of both the lake and the river system which connects that lake to the Mekong, a convergence that happens right in Phnom Penh.
The Tonle Sap system is unbelievable: because of heavy rainfall during the Summer Monsoon, the Mekong becomes engorged, to the point where it cannot accept extra water. Luckily, the Tonle Sap river can. So, this river changes direction, flowing ‘upstream’ and into the Tonle Sap lake, which expands to many times its breadth and depth.
This flooding of the lake brings with it tons of silt and other precursors to a healthy ecosystem, to the point that many academics have pointed to flood recession rice in the region as a form of sustainable agriculture indigenous to Cambodia. ((Fox, Jeff, and Judy Ledgerwood. 1999. Dry-season flood-recession rice in the Mekong Delta: two thousand years of sustainable agriculture? Asian Perspectives 38 (1):37-50. Note that this article is not actually about the Tonle Sap recession but about a site on the Mekong itself. The theory is largely the same, however)) The floods inundate bordering forestland, so that every year the forest becomes a magnificent place for fish to breed, making the Tonle Sap lake one of the most (the most?) productive freshwater fisheries in the entire world.
But of course, this is all changing rapidly. I have been writing jeremiads about the coming ecotastrophe for years now, to the chagrin of my friends (and possibly both of my blog readers), but even I had little understanding of the hard numbers behind the challenges we are all facing.
Lester Brown, of the Earth Policy Institute, has long been on the forefront of those who feel that we need to do something, sooner than later. Of course, as a lobbyist and a person who seems to believe in the ability of government to serve the people (seems to me like a case of asking the fox to babysit the hens), Mr. Brown relies mostly on ‘roadmaps’ of things that governments can do. In this he is much like the heroes and heroines of Kim Stanley Robinson’s excellent trilogy, Science in the Capital, which I just finished last week. But regardless of whom we both feel can and should do the heavy lifting, Brown is clearly a brilliant guy with his ear, quite literally, to the ground. I’m grateful for his work and his contributions.
And that is why I was horrified to read his latest essay on the water situation in the world, including a short paragraph on the relevance of it to the Mekong and the upstream dams in China (and other places). I had always paid significantly less attention, however, to the problems of draining our aquifers (we’ve just learned that the enormous aquifer that feeds much of the upper midwest is dangerously low, so this is starting to strike home, fast). His essay caught me up to a terrifying speed. Here’s the beginning, but I’d urge you to go read the whole thing yourself.
As the world’s demand for water has tripled over the last half-century and as the demand for hydroelectric power has grown even faster, dams and diversions of river water have drained many rivers dry. As water tables fall, the springs that feed rivers go dry, reducing river flows.
Scores of countries are overpumping aquifers as they struggle to satisfy their growing water needs, including each of the big three grain producers—China, India, and the United States. More than half the world’s people live in countries where water tables are falling.
There are two types of aquifers: replenishable and nonreplenishable (or fossil) aquifers. Most of the aquifers in India and the shallow aquifer under the North China Plain are replenishable. When these are depleted, the maximum rate of pumping is automatically reduced to the rate of recharge.
For fossil aquifers, such as the vast U.S. Ogallala aquifer, the deep aquifer under the North China Plain, or the Saudi aquifer, depletion brings pumping to an end. Farmers who lose their irrigation water have the option of returning to lower-yield dryland farming if rainfall permits. In more arid regions, however, such as in the southwestern United States or the Middle East, the loss of irrigation water means the end of agriculture.
The U.S. embassy in Beijing reports that Chinese wheat farmers in some areas are now pumping from a depth of 300 meters, or nearly 1,000 feet. Pumping water from this far down raises pumping costs so high that farmers are often forced to abandon irrigation and return to less productive dryland farming. A World Bank study indicates that China is overpumping three river basins in the north—the Hai, which flows through Beijing and Tianjin; the Yellow; and the Huai, the next river south of the Yellow. Since it takes 1,000 tons of water to produce one ton of grain, the shortfall in the Hai basin of nearly 40 billion tons of water per year (1 ton equals 1 cubic meter) means that when the aquifer is depleted, the grain harvest will drop by 40 million tons—enough to feed 120 million Chinese.
In India, water shortages are particularly serious simply because the margin between actual food consumption and survival is so precarious. In a survey of India’s water situation, Fred Pearce reported in New Scientist that the 21 million wells drilled are lowering water tables in most of the country. In North Gujarat, the water table is falling by 6 meters (20 feet) per year. In Tamil Nadu, a state with more than 62 million people in southern India, wells are going dry almost everywhere and falling water tables have dried up 95 percent of the wells owned by small farmers, reducing the irrigated area in the state by half over the last decade.
As water tables fall, well drillers are using modified oil-drilling technology to reach water, going as deep as 1,000 meters in some locations. In communities where underground water sources have dried up entirely, all agriculture is rain-fed and drinking water is trucked in. Tushaar Shah, who heads the International Water Management Institute’s groundwater station in Gujarat, says of India’s water situation, “When the balloon bursts, untold anarchy will be the lot of rural India.”
In the United States, the U.S. Department of Agriculture reports that in parts of Texas, Oklahoma, and Kansas—three leading grain-producing states—the underground water table has dropped by more than 30 meters (100 feet). As a result, wells have gone dry on thousands of farms in the southern Great Plains. Although this mining of underground water is taking a toll on U.S. grain production, irrigated land accounts for only one fifth of the U.S. grain harvest, compared with close to three fifths of the harvest in India and four fifths in China.