Being human, we tend to define "normal" by what we've become accustomed to over the previous generation or two. Unfortunately a span of 40 or 60, even 80-years isn't always a reliable yardstick.
A clear example of this is drought. Western North America has experienced unusually wet conditions over the past century. This extra precipitation has played a major role in the development of regions such as the US southwest. There have been droughts, such as in the Dirty Thirties, but overall those have been fairly rare and relatively brief events.
What these areas have not experienced in the past few centuries is mega-drought. Recently tree ring analysis has discovered that much of western North America endured such a drought from AD 900 to AD 1300. Four centuries of drought. Alberta is known to have had droughts that extended for almost sixty years.
The way we've developed the west hasn't taken drought into account. We've created "hyrdraulic" societies, communities whose very existence is dependent on groundwater irrigation. For decades we've been pumping water out of the acquifers faster than the recharge rate, continuously lowering the water table. Drought reduces the rate of recharge while simultaneously increasing our reliance on the groundwater reserves.
This year heralds what could be the beginning of a prolonged and severe drought in the west. From The Independent:
"From the mountains and desert of the West, now into an eighth consecutive dry year, to the wheat farms of Alabama, where crops are failing because of rainfall levels 12 inches lower than usual, to the vast soupy expanse of Lake Okeechobee in southern Florida, which has become so dry it actually caught fire a couple of weeks ago, a continent is crying out for water.
"In the south-east, usually a lush, humid region, it is the driest few months since records began in 1895. California and Nevada, where burgeoning population centres co-exist with an often harsh, barren landscape, have seen less rain over the past year than at any time since 1924. The Sierra Nevada range, which straddles the two states, received only 27 per cent of its usual snowfall in winter, with immediate knock-on effects on water supplies for the populations of Las Vegas and Los Angeles.
"...the long-term implications are escaping nobody. Climatologists see a growing volatility in the south-east's weather - today's drought coming close on the heels of devastating hurricanes two to three years ago. In the West, meanwhile, a growing body of scientific evidence suggests a movement towards a state of perpetual drought by the middle of this century. 'The 1930s drought lasted less than a decade. This is something that could remain for 100 years,' said Richard Seager a climatologist at Columbia University and lead researcher of a report published recently by the government's National Oceanic and Atmospheric Administration (NOAA).
"'A lot of people think climate change and the ecological repercussions are 50 years away,' Thomas Swetnam, an environmental scientist at the University of Arizona in Tucson, told The New York Times a few months ago. 'But it's happening now in the West. The data is telling us that we are in the middle of one of the first big indicators of climate change impacts in the continental United States.' Across the West, farmers and city water consumers are locked in a perennial battle over water rights - one that the cities are slowly winning. Down the line, though, there are serious questions about how to keep showers and lawn sprinklers going in the retirement communities of Nevada and Arizona. Lake Powell, the reservoir on the upper Colorado River that helps provide water across a vast expanse of the West, has been less than half full for years, with little prospect of filling up in the foreseeable future.
"According to the NOAA's recent report, the West can expect 10-20 per cent less rainfall by mid-century, which will increase air pollution in the cities, kill off trees and water-retaining giant cactus plants and shrink the available water supply by as much as 25 per cent.
Shrinking the water supply by 25% sounds serious but it's made worse by the reality that the current water demands already well exceed today's supply. Sooner or later something has to give. Either demand for water will have to be drastically cut or - wait for it - sources of freshwater will have to be found elsewhere.
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