And with more than 23 million more residents expected to live in the region by 2030, resources will become increasingly stressed.
"[G]iven the International Panel on Climate Change's warnings about anthropogenic global warming and a well-documented expanding drought, residents of the West are not just living on borrowed water, they're also living on borrowed time.
Glen MacDonald is the director of the UCLA Institute of the Environment and Sustainability and an international expert on the effects of climate change and drought. He says that the best climate models that exist predict the 21st century is likely to be increasingly arid if greenhouse gases increase. But discounting that, MacDonald says we can expect more severe and longer-lasting droughts than occurred in the 20th century.
'It all adds up to the fact that we have to do some very, very serious long-range water resource planning,' he says."