The Great Thirst
By admin on Jan 20, 2007 | In *Climate, *Sustainability
The Great Thirst
Looking ahead to a post-global warming life in California, 60 years hence
Glen Martin
SF Chronicle
Sunday, January 7, 2007
The following extrapolation presents a worst-case scenario of California's water situation in the coming decades, but not necessarily an unlikely one. It is based on a variety of sources, including interviews and conversations over the past several years with scientists and government agency staffers, such as those associated with the University of California, the California Department of Water Resources and the Bay Institute. (The observations of Jeffrey Mount of UC Davis and John Harte of UC Berkeley were particularly enlightening.)
ED NOTE: An excellent article, well researched on California water issues 50 years from now. This is a must read.
Follow up:
Various textual sources -- including white papers produced by the state's Climate Action Team -- were also a source of both statistics and inspiration. The Climate Team reports, prepared for Gov. Arnold Schwarzenegger and the state Legislature before the drafting of the 2006 Global Warming Solutions Act, postulate likely impacts of global warming on precipitation patterns, water availability, hydroelectric power, forestry and agriculture. Few of the conclusions are comforting.
Finally, I must acknowledge that my field observations from two decades of reporting on water played a role in this soothsaying exercise. The main thing I've learned is that larger trends don't necessarily translate into predictable regional events. Global warming likely will result in somewhat drier winters and less snowpack for the Sierra; strong El Niños, also predicted in most current global warming projections, mean wetter, warmer winters for the North State. I've tried to reconcile these two seemingly disparate projections in this piece.
I've also learned that nature invariably seeks and exploits the weakest link. I still remember the panic engendered by the second year of the 1976-77 drought. And I recall covering the great floods of 1997, the year, some experts say, we came close to losing Sacramento.
One day that winter, I stood on Highway 70 at the point it disappeared into a roiling inland sea, the outflow of the Feather, Yuba and Bear rivers. Among the flotsam were trailer homes and huge propane tanks, venting gas as they rolled in the brown water. Submerged beneath the flood was the little town of Olivehurst. Then, it was a mere hamlet surrounded by croplands. Today, it is a residential tract boomtown. The engineers say the new levees they are constructing will withstand anything the rivers deliver. I wonder.
-- Glen Martin
It is a sign of the flexibility of the human spirit that a certain nostalgia has begun to pervade our memories of the Great Thirst. With it immured safely 30 years in the past, we can afford such revisionism. Today, in 2062, we delight in recalling the heroic incidents it kindled, the ingenious responses to catastrophe, the shared privations. Now that we have squeezed through the bottleneck with our institutions more or less intact, we can savor the simple and glorious fact that we endured.
But as we bask in the alpenglow of our memories, we must acknowledge that the forces that almost destroyed California are still in play globally; that other people are still grappling with the crises we have weathered. They still have to get though the bottleneck.
True, we Californians have established the standard for societal response to catastrophic water shortages and supply disruption. But we had an essential advantage: We were Californians. Our state was -- and is -- one of the world's great repositories of wealth, technology and talent. We had everything going for us, and we still barely squeaked through.
Nor can we claim that we emerged unscathed. Our society has changed, and not necessarily for the better. Our lives are tightly regulated now, in ways our antecedents would not have tolerated. Key components of the old economy have disappeared. The environmental disruption of the past five decades has been extreme, and much of the damage is irreparable. There are far more of us living on much less. Basic services and resources that were once considered an unalienable birthright are now privileges: Only the very wealthy have swimming pools or lawns.
Still, we all have enough water to drink now. All of us can shower regularly, and we can flush our (reduced flow) toilets after each use. We can wash our clothes more or less when we want. Yes, we pay a lot of money for our water, but we're used to it -- as our grandparents became inured to paying top dollar for gasoline. After years of dire shortages and draconian rationing, the simple fact that we can turn on a tap at will seems like a luxury of the most decadent stripe.
The irony, of course, is that the Great Thirst initially wasn't driven by water shortages. For thousands of years, the west slope of the Sierra Nevada annually produced about 30 million acre-feet of runoff. Winters have become somewhat drier during the past 50 years, but the Sierra still yields on average about 25 million acre-feet of water a year. So the issue isn't so much about the amount of water -- it's the way nature delivers it that has radically changed, and that has made all the difference. (Climate Scenarios for California, California Climate Change Center, 2006)
Many scientists saw it coming, positing as early as the late 20th century that global warming due to greenhouse gas emissions would change the precipitation pattern in the Sierra. And by 2020, the emerging pattern became clear: More moisture falling as rain rather than snow at the higher elevations. (Interview with John Harte, UC Berkeley)
This basic fact radically changed the way water was delivered to California's reservoirs. When the state's reservoir system was conceived, it was designed to hold water from spring snowmelt. Because it typically took several weeks for the snowpack to melt, the reservoirs could be filled gradually through the late spring. The water was then released for hydropower, agricultural irrigation and urban requirements through the summer and early fall, when needs were at a peak.
But the shift in the weather regimen rapidly made the system obsolete. Instead of falling as snow for later and manageable downstream flow to the reservoirs, the precipitation began falling as rain. What fell at high altitudes raced instantly downstream, all through the vast watersheds of the Sierra. The reservoirs were changed from water-storage systems to flood-control structures, holding back the torrents only enough to prevent catastrophic flooding through the Central Valley. Most of the water had to be passed downstream, through San Francisco Bay and out the Golden Gate. It could not be saved for summertime irrigation, power and urban uses. (Paper by Edwin Maurer and Philip Duffy; Geophysical Research Letters, Jan. 27, 2006) By the third decade of the century, the state had begun its slide toward water deprivation: Even during extremely wet winters, we simply could not hold on to the precipitation. Overall, annual water deliveries in the state had declined an average of 20 percent by 2030. (Climate Warming and Water Supply Management in California, California Climate Change Center, 2006)
Snow still accumulated in the Sierra -- but as the years went by, it tended to accumulate only briefly, and only at the highest elevations. Even then, it merely compounded the problems rather than ameliorating them: Any snow lying around was sure to be drenched in short order by warm rain, sending even bigger pulses of water into the already stressed reservoirs. Worse, as predicted by most global warming models at the beginning of the century, the incidence of El Niño years increased for the eastern Pacific. These intrusions of warm marine water to our coast left the door open for countless "Pineapple Express" storms that dropped huge amounts of warm precipitation on the state, far more than is typical for northern storms. (Maurer/Duffy: Geophysical Research Letters, Jan. 27, 2006)
So even as California inched toward summer water shortages, it was sometimes drowning during the winter. At this point, many pundits opined the state could adjust to the new precipitation patterns by building more reservoirs on major rivers to improve flood control and increase water storage capacity. The negative environmental impacts of such projects were openly acknowledged, but advocates claimed the very social fabric of the state was at stake. Their arguments convinced many Californians, and it seemed clear that legislation or bond initiatives eventually would be passed for new dams and delivery systems. Then came the winter of 2033-2034.
Again, the events that transpired in mid-February had long been foretold. More than 30 years earlier Jeffrey Mount, a UC Davis geologist, had predicted similar scenarios with almost preternatural accuracy.
The rains came early that year, following a fierce El Niño. In November, the first of a great train of subtropical storms swept in from the south-central Pacific. By Thanksgiving, the state was drenched, and by early December it was waterlogged. Every river from the McCloud in the north to the Kern in the south was swollen and turbid with runoff.
The storm door remained open through Christmas, but it abruptly canted north. Everyone breathed easier as the snow began to accumulate in the Sierra. There had been some levee breaches in the Sacramento-San Joaquin River Delta and in the northern San Joaquin Valley, but crews immediately began plugging them.
The snowpack grew through late January as front after front moved down from the Gulf of Alaska; drifts were 20 feet high at Donner Summit. Ski resorts, impoverished by years of scant snow, declared the return of the Glory Days.
But while skiers and snowboarders responded, the crowds were considerably reduced from those of three decades earlier. (Interview with Harte) The Sierra, once a global destination for winter sport enthusiasts, now suffered from a reputation for meager snow and unreliable conditions. Instead of zipping up to Tahoe for the weekend as was once the norm, skiers and snowboarders now tended to save their money for extended trips to destinations that still had prime snow -- the Canadian Rockies, Alaska -- and for those who had the funds, Patagonia or New Zealand.
Still, the skiing was superb in late 2033 and early 2034. Then in the second week of February, the storm track swung south again. Front after front still rolled through, battering the west slope of the Sierra -- except now, as was the case in November and early December, they came from the central Pacific. They were warm, and the copious volumes of moisture they contained all fell as rain or sleet -- even at 7,000 feet. From Tahoe to the Tehachapis, the snowpack melted as though a blowtorch had been held against it.
In the Sacramento Valley, Shasta Dam on the Sacramento River and Folsom Dam on the American River had been dumping steadily since the heavy fall rains, but their reservoirs were still high. Now, with an entire season of snowmelt pushing downhill in a matter of days instead of weeks, they proved insufficient to avert catastrophe.
Shasta Dam held against the torrent, thanks to a huge reservoir and a strong, high dam. But it was barely able to keep up with its inflows, and its gates ran wide open. The Sacramento River boiled near the top of its sodden levees all the way to its confluence with the Feather River, which was in turn dumping water from the Feather and Yuba watersheds at the rate of hundreds of thousands of cubic feet a second.
Marysville and Yuba City were inundated by the flood. South of Marysville, near the former farming hamlet of Olivehurst, a vast warren of residential tracts had sprouted on the rich loam, protected by levees that had been declared impregnable when they were built 25 years before. Now these berms melted before the surge, and the developments utterly disappeared beneath the water. The floods claimed 600 lives in the greater Marysville area.
A great deal of water was diverted to the Sutter and Yolo bypasses, but it wasn't enough. Most of the Sacramento River's flow still pushed to the heart of the city of Sacramento -- where the American River entered from the east. Here, Folsom Dam quickly revealed its deficiencies. (1998 Field Hearing on Proposed Modifications of Folsom Dam; Subcommittee on Water and Power of the Committee on Resources, U.S. House of Representatives)
Folsom Dam was lower than Shasta Dam, and it backed up a much smaller reservoir. Folsom had been raised in 2022, and was considered sufficiently bolstered to handle 200-year floods. But that analysis was based on historic data mostly gathered from the 19th and 20th centuries. The quixotic weather that now seemed a corollary of global warming had not been taken sufficiently into account. By the old criteria, the water now booming down the American River was not a 200-year flood -- it wasn't even a 500-year flood. It was, at the least, a millennial flood. More than 200,000 cubic feet of water per second was coming down the American.
And it went over Folsom Dam. More accurately, it undercut the earthen flanks of the structure. Folsom Dam became nothing more than a diversion in the flow, like a mid-stream boulder. Sacramento braced briefly against the walls of water approaching it from the north and east -- and yielded. The two great rivers claimed the city as their own, turning it into a muddy torrent up to 2 miles wide. In the Natomas area, the water stood 20 feet deep. As we now know, at least 4,000 people died in Sacramento. The state government was moved temporarily to San Jose.
The drowning of Sacramento still stands as the country's worst civil disaster. It is marked on our calendars, and state schoolchildren and government employees get the day off. But it was not, of course, the most far-reaching consequence of the February Flood. The bitter irony is that the flood, an epochal manifestation of fresh water, marked the beginning of the Great Thirst.
While the Sacramento and American rivers were destroying the state capital, the San Joaquin River to the south was also in extreme flood stage, bolstered by the contributions of its mighty tributaries: the Merced, Tuolumne, Mokelumne and Stanislaus rivers. By the standards of the Sacramento Valley, most of the levees of the San Joaquin Valley were pathetically under-engineered. And even relatively new levees that were designed to handle anything nature could throw -- the "super levees" surrounding the huge housing tracts near Lathrop, for example -- proved dismal failures. The river conquered all, and surged into the Sacramento Delta.
And here, the tipping point was achieved -- and a new equilibrium established, one inimical to civilization as we knew it in early 2034. (Interviews with Jeffrey Mount, UC Davis)
The central fact driving the change: Most of the delta's agricultural islands had subsided drastically from more than a hundred years of farming. They were essentially holes in the ground protected by weak levees; some were 20 feet below sea level.
Additionally, water levels were rising in the delta. For 20 years, sea levels had been climbing due to massive polar ice cap melting -- again, attributed to global warming. The rise, modest in annual increments, was significant in the whole: Between 2000 and 2030, sea levels at San Francisco Bay had risen 6.5 inches. (Projecting Sea Level-California Climate Change Center) The higher mean water levels had weakened all the westernmost levees drastically -- they desperately wanted to fail.
And the San Joaquin River obliged them, smashing the levees and flooding the islands, abruptly changing the delta from a patchwork of farmland, canals and sloughs into a vast, saline bay. To the north, the Sacramento River added its flow, compounding the disaster. (Interviews with Mount)
The bay now surrounded the great state and federal pumps near Tracy. The gigantic apparatus that delivered freshwater from the north state to the farms and cities of the south ground to a halt. The pumps could now send only salt water south; they were useless.
The storms eventually blew themselves out and the rivers stopped raging. California buried her dead. But that all ended up as subtext as the full impact of the destruction of the state's primary water delivery systems became apparent. Full water rationing immediately went into effect for the East Bay and most cities south of the delta. Irrigation deliveries to the west side of the San Joaquin Valley were curtailed -- after state and federal legislation passed compensating farmers for that year's crop loss.
In the first weeks following the flood, both the governor's office and the state Legislature unexpectedly showed their mettle, forsaking their interminable squabbles to address the disaster.
Immediately on gaining her new authority, she conferred with and received support from the U.S. Bureau of Reclamation, which controls many of the Sierra's reservoirs. She then approved diversion of all water from Millerton Reservoir on the San Joaquin River to the Cross Valley Canal, (currently in use) which connected to the California Aqueduct -- at that point a dry, worthless ditch, since water no longer flowed from the delta.
Her move dried up eastern San Joaquin Valley farms, but it allowed the continued delivery of water over the Techachapis to Los Angeles and its satellite communities. The governor also directed all Colorado River water deliveries away from Imperial Valley farms to the south state's biggest municipalities. Californians were by no means comfortable in the summer and fall of 2034. Their lawns were brown and their cars were filthy -- but they at least had enough water for drinking, short daily showers and semi-regular toilet flushing.
That might have been enough to allow the state to limp through the next few years, until water supplies could be judiciously re-allocated, affected parties made whole and new delivery systems built. But the governor and lawmakers didn't enjoy such a leisurely interregnum between one disaster and the next. In early 2035, just as it seemed the economy and citizenry were settling down, something became distressingly clear: Virtually no precipitation had fallen that winter. A high-pressure system of unparalleled stability was locked over the eastern and north Pacific. California had lurched from one of the wettest years on record to one of the driest. The drought that loomed promised to be as severe as the great drought of 1976-77, the first inkling modern Californians had that the Golden State was, at heart, a desert state.
In fact, the drought was worse than the '70s dry spell. It ominously hinted at the multi-decade droughts that research indicated had blighted California roughly between A.D. 1100 and 1350. (Scott Stine, Nature, 1994)
For four years, only a few storms hit the Sierra, and they were paltry. By the end, all the state's reservoirs were bottoming out. The San Joaquin was a dirt-bike track its entire length; the Sacramento had been reduced to a trickle. Before, people were inconvenienced; now, they were panicked. In the months after the flood, the issue was about obtaining sufficient water for a reasonably civilized life. Now it was about raw survival.
Some urban areas ran dry, and had to be serviced with tanker trucks. Freelance, or "gypsy," tankers catered to the poorer neighborhoods, selling their cargo at exorbitant prices. That triggered the Water Riots of the summer of 2038, when much of Los Angeles burned.
Agricultural production collapsed. Once the salad bowl of the nation, California was now importing most fruits and vegetables. Produce prices skyrocketed. Yet state farmers, paradoxically, did fairly well, at least those with primary water rights. After some brisk legal skirmishes, those rights generally were upheld -- and the farmers who possessed them prospered, selling what water they had at astronomical rates to the cities. (Climate Warming and Water Supply Management in California, California Climate Change Center)
Water became the new gasoline, every drop precious and hoarded. Dishes and clothes were all washed by hand now, and the gray water saved to irrigate window pots of herbs and greens or to flush toilets. Showers became a fond memory. The sponge bath was the new standard: One small saucepan of water to wash, with a cloth, bar of soap and shampoo; one larger pot to rinse. Again, the gray water was saved. Thousands of new wells were drilled throughout the state in a desperate bid to tap groundwater. This provided brief relief in some cases, but the exponential increase in demand tapped out water tables, and soon the new wells were sucking air.
At this point, California's 50 million citizens seemed to take a collective deep breath and consider their options. About 8 million of them -- mostly the poor, unemployed and hopeless -- decided they'd had enough. What then transpired was like the Okie exodus of the Dust Bowl, except in reverse. Caravans of the disenfranchised clogged the freeways and blue highways heading east.
As they traveled, they found drought had gripped the Southwest, the Rocky Mountain states and the Great Plains as viciously as it had California. Before its extensive settlement in the mid-19th century, the American West had been called the Great American Desert. It was now clear those early evaluations were accurate. Most of the emigrants didn't stop until they were well beyond the Mississippi River, where the rains still fell reliably. America was not ready for these new armies of the poor and desiccated. Huge encampments sprang up along Eastern freeways, especially along Interstate 80 from Illinois to Pennsylvania. These ragged immigrants had no money, and their collective skill set was low. Their demands on local communities -- for shelter, food, funds, jobs, medical care, schooling -- was great, in some cases insupportable. Local resentment against them ran high. It took a full generation to absorb the "Calies" into their new environs, and the process was trying, at times traumatic, for all involved.
Meanwhile, back in California, the governor had begun running into resistance from state legislators on long-term responses to the drought. So -- as other California governors had done in the past -- she appealed directly to voters, promoting a series of referenda that would utterly revamp the state's water storage and delivery system.
Among the initiatives was one that greatly increased the power of the governor's office. This, she said, would allow her to do what had to be done to get California rehydrated: override a vacillating and feckless Legislature and definitively cut the Gordian knot of environmental regulation.
The remaining initiatives were bond measures and levies that would fund the largest public works effort in state history -- a veritable Manhattan Project for water.
Under the governor's plan, a peripheral canal would be dug around the delta, providing a new south state delivery conduit for the Sacramento River.
Just as bold: Every major river canyon on the west slope of the Sierra would be turned into catch basins for winter and spring precipitation. Altogether, five new dams would be built on the major west Sierra drainages. The measures also included plans for reservoirs on some of larger streams on the east slope off the Coast Range, such as Putah Creek and Cache Creek. (Scenarios of Climate Change in California: An Overview, California Climate Change Center)
New water standards were required for toilets, dishwashers and washing machines. Provisions were also made to retrofit most major urban water treatment complexes to render sewage and storm runoff fit for reuse, with the recycled water employed for agriculture and landscaping.
Finally, the initiatives provided for ambitious groundwater storage projects. Under the measures, many of the areas that had been sprawling housing tracts before the February Flood would now be permanent bypasses, zones where flood waters could be diverted and held until they percolated downward, recharging water tables. These areas, the governor declared, could be managed for wildlife habitat as well as water storage.
Altogether, the initiatives would raise $300 billion through bonds and new taxes, greatly increasing the state's debt and further burdening businesses and workers.
The governor pointed out she had received guarantees the federal government would provide up to $100 billion in matching funds. Further, she said, the bonds and taxes were a necessary investment, essential to assuring not California's prosperity, but its simple existence as a modern society.
Environmentalists rallied to fight the initiatives. They pointed out the effects of a peripheral canal on the delta and San Francisco Bay were unknown, (various interviews with staffers of the Bay Institute and the Pacific Federation of Fishermen's Associations) and that the Sierra's great river canyons would be lost to chains of reservoirs. They also noted no provisions had been made to maintain water deliveries from Shasta Dam for Sacramento River Chinook salmon -- runs that had been painstakingly revived over five decades. Fearing the worst, they hastily drafted an initiative of their own, specifying any new dam projects must include fishery maintenance flows for the Sacramento and San Joaquin rivers.
Conservationists also claimed the new reservoirs would add significantly to the state's global greenhouse gas emission load, undermining the Global Warming Solutions Act of 2006. The decaying trees and other vegetation in the new reservoirs, they said, would release large amounts of methane and carbon dioxide into the atmosphere. (Philip Fearnside: Greenhouse Gas Emissions From a Hydroelectric Reservoir; Water, Air and Soil Pollution Journal, 2002)
The governor countered somewhat disingenuously that the carbon-free hydroelectric power yielded by the new dams would help offset the added greenhouse gas releases. Besides, she once again emphasized, she had no choice but to proceed with her plans.
Even before the flood and drought, California residents had been leaning toward dam construction. Now, with empty reservoirs and a devastated economy, they saw things the governor's way. Her "Healing Waters" initiative package passed in a landslide. Of some small relief to environmentalists was the narrow passage of the Sacramento-San Joaquin salmon initiative. In a magnanimous move, the governor said fishery flows down both rivers were sacrosanct, and would be maintained.
Simultaneously, the state's local governments and residents responded to the water crisis on their own. Marin County had long maintained a desalinization plant to supplement water supplies during dry years, and now it built a huge new complex, capable of providing up to 60 percent of county needs. The water was expensive -- up to $1,500 an acre foot (Climate Warming And Water Supply In California, California Climate Change Center), exponentially more costly than water from most other sources. But county residents could afford it, and were happy to pay for the peace of mind the new plant provided. Other wealthy coastal communities, most notably Santa Barbara and San Diego, followed with big desalinization plants of their own.
The Great Thirst also revived an ancient technology: cisterns. Across the state, the roofs of homes and commercial buildings were covered with sheet metal or treated with special polymer coatings, and their gutters and downspouts connected to plumbing that emptied into newly constructed concrete or stainless steel cisterns. Such systems were simple to install and maintain, and the water they provided required little treatment. Tens of thousands of acres of roofs eventually were outfitted in this way, and the yield was impressive: 550 gallons of water for each inch of rain falling on 1,000 square feet of roof. (Rain Catchment Systems/The Campus Center for Appropriate Technology, Humboldt State University) Many homeowners found their cisterns provided a significant fraction of their water requirements.
Other avenues were tried and abandoned. These include solar stills for distilling gray water; a "still suit" -- modeled after those described in the science-fiction novel "Dune" -- that was designed to turn sweat, urine and respiratory vapor into potable water, but did little more than make its wearers reek like actively fermenting compost piles. And most notably, the Berg Project.
This plan to wrap Arctic icebergs in heavy-gauge plastic sheeting and tow them to water-deprived southern cities had been kicking around for decades, (Time magazine, Oct. 17, 1977), but the Big Thirst gave venture capitalists impetus to back a pilot effort. It was an abject failure, from start to finish: The towlines kept breaking in heavy seas; the ice melted far more rapidly than expected, and was lost as leakage. The expenses were so high that the much-reduced berg that finally made it to San Francisco Bay wouldn't have covered costs had it been sold as mere drinking water. Investors made most of their money back by selling small vials of the ice melt as tourist souvenirs.
Much has been taken from California by the Big Thirst. We have lost the deep, wild canyons of the Sierra. Hobbled by both regulation and new social mores, our lives are more constricted. For most of us, such simple pleasures as a flower garden or a prolonged soak in a big tub are no longer affordable.
But our optimism has returned. After all, we have been able to save -- even augment -- some of the best things of the past. We still have our wild salmon fisheries, albeit at reduced levels. The huge new Sacramento and San Joaquin bypass system has created thousands of acres of wildlife habitat and parks on land where housing developments once sprawled. The economy has recovered, driven in large part by the research and technologies that emerged here as a response to the floods and droughts.
We shouldn't assume, however, that we have bested Nature at her game. We have water now, but barely enough -- and our population is once again growing, today standing at about 55 million. The planet is still warming, with consequences for California that are unlikely to prove benign. It is increasingly clear we haven't really solved our water crisis -- we have simply negotiated a respite. And we have no clear idea where to go from here.
From 2035 to 2064, Sierra snowpack is expected to decrease 12 to 47 percent from historic levels. By the end of the century, annual snowpack could decline by 90 percent.
Source: California Climate Action Team reports
By the mid- to late century, reservoir inflows are expected to decline in spring and summer and increase in winter. In the most extreme model, the month of highest streamflow would shift from May to February.
Source: California Climate Action Team reports
Flows into major Sierra reservoirs could decline 25 to 30 percent from the middle to the end of the century.
Source: California Climate Action Team reports
Before the end of the century, sea levels are expected to rise 5.1 to 24.4 inches from the 2000 mark.
Stress on tidewater levees in the bay and delta will increase with every inch of rise.
Source: California Climate Action Team reports
Within the tenure of human habitation, California has suffered severe droughts lasting more than a century. A study of relict tree stumps recovered from lakes and marshes indicates the Sierra Nevada endured an extreme drought of more than 200 years before A.D. 1112 and another lasting more than 140 years before A.D. 1350
Source: Scott Stine, Nature, June 16, 1994
How the water flows
Each year, the Sierra snowpack provides about 30 million acre-feet of water for human use - but that figure is expected to decline under most global warming scenarios.
Warmer winters are also likely to deliver more rain than snow to the Sierra. This will make it more difficult to store water in reservoirs, because the flow schedule will be compressed, moving from late to early spring - or even late winter. Stream flow levels will be higher in this shorter runoff season, meaning reservoirs may have to be used more for flood control than water storage.
Warmer winters and less available water will increase pressure for more water storage and production facilities - new reservoirs, canals, extensive groundwater recharging schemes and desalinization plants. Yet this may not prove sufficient to avoid severe social and economic disruption, and environmental costs for such projects could also be high.
There also remains the nagging reality that much of California is desert or semi-desert, and that the entire state is vulnerable to drought. Particularly disquieting is evidence that California endured extreme droughts lasting several decades only a few hundred years before it was first explored by Europeans.
Sources: ESRI, Chronicle research
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