India, April 19 -- T hey say: "Follow the river and it will eventually lead you to the sea". This is no longer true in parts of the world. For nearly 6 million years, the Colorado river (right) flowed from the Rocky Mountains into the Gulf of California. Over the past 20 years, it has seen volumes drop by 20%, and it now runs dry almost 160 km before it reaches the sea. Irrigation consumes more than half the river's water, with much of this used to grow cattle-feed crops. Another tenth is claimed by evaporation at dam reservoirs, with another 20% supplied to households and industries. Meanwhile, more than half of the Western United States is currently experiencing drought conditions, following a winter of historically low snow, according to...