Notorious for its annual floods, Bangladesh may seem the last place in the world to worry about a drying up of the rivers that flow from the Himalayas. But the country is as much at risk from drought as it is from flooding. Already farmers who used to grow rice have turned to farming prawns because the water in their fields has turned so salty nothing will grow there. Bangladesh is the front line of global warming, with rivers drying up, and increasingly common freak weather conditions that include out-of-season tornadoes and tides that have stopped changing. The entire country is one huge delta, formed by the Ganges, Brahmaputra and Meghna rivers. Flooding may seem to be Bangladesh's greatest enemy, but in fact the rivers are its lifeline. They are the main source of fresh water for a country where agriculture represents 21 per cent of the economy. And environmentalists fear that if the Himalayan glaciers melt, the rivers' flow will reduce drastically.