Rivers Run Dry

Using this much water is disastrous for many of our rivers. I stood on the banks of the Rio Grande in Texas near a small dusty town on the US-Mexican border called Presidio. This area, locals told me, had been farmed for more than 400 years - probably longer than anywhere else in the US. I was with farmer Terry Bishop. He was bankrupt, despite owning a large chunk of prime Texas farmland. His problem was that his legal entitlement to the waters of the Rio Grande was useless. There was no water in the river. Dams upstream capture all the water from the river for delivery to cities and farms.

The mighty Rio Grande is now, in fact, two rivers. The main US arm, rushing down from of the Rockies, gives out just past El Paso, 1000 kilometres from the Gulf of Mexico, where it once reached the ocean. Its bed is then dry for 300 kilometres, until just past Presidio. There it is replenished from Mexico by an old tributary, the Rio Conchos. Atlases may show a river passing Terry Bishop's land, but in fact the river bed is dry there most of the year.

In India, where most of the rivers have long-since dried up, the underground water reserves are being emptied. A century ago, British colonial engineers built the largest network of irrigation canals in the world. They grew crops to feed the empire. But today there is not enough water for many of those canals, because the new crops are more thirsty.

Most farmers are now pumping water from ancient natural reservoirs beneath their fields. In the past decade, more than 20 million farmers have bought drills to tap that water, and cheap Japanese pumps to bring it to the surface and water their crops. Water tables that were until recently only a few metres below the surface are now hundreds of metres down.

Right now the farmers can mostly keep getting water so long as they keep drilling deeper. But how long can it go on? In Gujarat, one of the states worst affected, I visited Tushaar Shah, who runs a groundwater research centre funded by the World Bank. He calls the pumping bonanza 'A colossal anarchy; a one-way trip to disaster.' He reckons farmers are taking from underground reserves 100 cubic kilometres of water more every year than the rains replace. It's hard to imagine a number like that, but it's a lot of water. In Britain, we uses only about 15 cubic kilometres of water a year for absolutely everything.

India feeds itself, these days. But India's green revolution is living on borrowed water and borrowed time. And dozens of other countries in Asia are going the same way as the rivers run dry. In Pakistan, China, Vietnam and Iran underground water is being used up fast.