Weatherwatch: arid American west expands eastwards

Water supplies in western US will become more precarious amid warming climate

Los Angeles should not exist. The explorer John Wesley Powell warned the US Congress 140 years ago that the American west was a harsh arid land and settlements should be limited to conserve scarce water supplies. The politicians rejected his advice and launched a massive programme of dam and canal construction for irrigation and settlements.In a gruelling expedition across North America, Powell had seen a dramatic transition from the lush green prairies in the east to the dry lands of the west, and the frontier of this transition was the 100th meridian, an invisible line of longitude passing north-south through North America.