Last March, after a series of cold winter storms, the snowpack in the Sierra Nevada was above normal. That seemed to be good news for the state's water supply, which relies heavily on Sierra Nevada snow.
But after a record heat wave in the early spring, it was as if the winter's big storms had never happened. Only about 40% of the snow's water content -- far less than usual -- ended up in rivers and reservoirs. The parched ground quickly absorbed some of it, and more evaporated because of the high temperatures.
If the same things happen this year -- and they may well despite the recent rains -- Southern California will face a regionwide water shortage for the first time since 1991.
The vanishing Sierra snowpack could be a symptom of climate change, and it's not the only one. Downstream, the Sacramento-San Joaquin River Delta, the hub of California's water system, is in severe environmental distress. And Southern California groundwater basins and reservoirs aren't being replenished most years.
In an attempt to avert water shortages for consumers and businesses, the Metropolitan Water District of Southern California depleted its water reserves last year at the rate of 523 million gallons a day. But that can't go on indefinitely without the tap running dry.
The way Californians have been using water is simply not sustainable. We have no choice but to use less and to pay more for it.
The West was settled during an unusually wet period in its history. Today, we're alarmed by a three-year drought, but there is ample geologic evidence of previous droughts measured in decades.
In Los Angeles this month, Mayor Antonio Villaraigosa called for new water restrictions and penalties for those who fail to conserve, but the measures would just be a beginning. Consumers need to understand that conservation is no longer a personal virtue; it is a civic necessity. And local water districts throughout the state must find ways to lower demand by encouraging more efficient use of water.
In Southern California, the population within the MWD's six-county service area grows by about 200,000 people a year. Some of the necessary "new" water to meet their needs will come from super-treating waste water to produce supplies that exceed every drinking water standard (if astronauts can drink it, why can't the rest of us?). Some may come from desalination of ocean water. Some must come from cleaning up contaminated groundwater basins. Increasing our local supplies can be a powerful hedge against uncertainties elsewhere.
The region has not experienced the reality of water limits and widespread mandatory conservation for nearly a generation. We have never squarely faced the future. Water projects built Southern California. Now we need water stewardship to sustain it.
William Patzert is an oceanography research scientist at Caltech's Jet Propulsion Laboratory in La Cañada Flintridge. Timothy F. Brick is the chairman of the board of directors of the Metropolitan Water District of Southern California.