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The Big Heat - Global Warming, and the Portfolio-Based Approach in the Bay-Delta

Barry Nelson

Posted February 8, 2013

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NRDC recently joined a coalition of water agencies, business leaders and environmentalists in releasing a new approach to address the challenges facing the San Francisco Bay-Delta estuary.  The press around Bay-Delta issues often revolves around current developments about endangered species, this year’s salmon fishery and last month’s snowpack.  These are important issues, but one of the major reasons California needs a comprehensive plan for the Bay-Delta is our growing understanding that a warming climate will have profound impacts on this ecosystem and on the people who depend on it.  A quick review of these likely impacts reveals more reasons why the new portfolio-based conceptual alternative is a smart direction for California water policy.

California has done more than most states to understand the possible impacts of climate change on water resources.  For example, in 2006, the state Department of Water Resources developed a lengthy document regarding Progress on Incorporating Climate Change into Management of California’s Water Resources.   That document identified a number of important potential impacts on California water.  It’s worth taking a moment to review some of those impacts – and how the new portfolio-based approach can help us prepare to meet water and environmental needs in a warmer future.

Rising Seas:  Sea level at San Francisco’s Golden Gate has risen by 7 inches in the past century.   The state’s Ocean Protection Council anticipates an increase of 10 to 17 inches by mid-century and 31-69 inches by 2100.  These rising seas will place significant additional pressure on the vast network of levees that protects subsided Delta islands from flooding.  An analysis by the University of California projects the likelihood of a large-scale Delta levee failure at two-thirds by 2050.  Such a failure could have disastrous impacts on the ecosystem, on Delta farms and residents, on infrastructure and on the state and federal water pumps in the South Delta. 

  • Portfolio-Based Solutions:  The new portfolio-based approach would meet the sea level rise challenge in several ways. A billion dollar investment in Delta levees would reduce the risk of a catastrophic levee failure.  A new 3,000 cfs water conveyance facility in the less vulnerable north Delta would provide an important lifeline to keep water flowing in the event of a levee failure. And one million acre-feet of new South of Delta water storage would provide emergency supply in the event of a disaster in the Delta.  In short, this portfolio would reduce the risk and consequences of a levee failure as a result of sea level rise.

Reductions in Water Flows:  Climate change can reduce available water in California in several ways.  Global warming will changing the timing of runoff, with more coming during winters with more rain and less mountain snow.  Increased evaporation from hotter watersheds may reduce the percentage of precipitation that flows into streams.  And changes in global circulation patterns could reduce total precipitation.  Back in 2006, the DWR report cited above stated that the “central tendency in the projections is toward moderately decreased precipitation.”  The US Global Change Science Program has projected a 5-10 percent decrease in California runoff.  These conclusions are also reflected in a 2012 analysis prepared by UC Davis for the California Energy Commission.  Table 5 in that document suggests that average annual natural river flow in the Bay-Delta system could drop by approximately 3 million acre-feet by 2051-2100.   As in the case of the Colorado River, California shouldn’t plan to squeeze more water from a drying Bay-Delta ecosystem.  

  • Portfolio-Based Solutions:  This new conceptual alternative proposes a five billion dollar investment in agricultural and urban water conservation, water recycling and other proven tools.  One advantage of these tools is that they will be far less affected by a changing climate than will our river flows.  In fact, because evaporation and plant transpiration is expected to increase as temperatures rise, planting more efficient landscapes around our homes and businesses will save even more water in the future.  These investments in climate change resistant water supplies can dramatically reduce our reliance on climate change vulnerable systems like the Bay-Delta, providing abundant, reliable water supplies to help keep California’s economy humming.                                                                                        

Greater Extreme Weather Events – More Floods and Droughts.  Have you heard the old joke about the statistician who had his feet in the oven and his head in the freezer? “On average,” he said, “I’m quite comfortable.”  Well in the case of water supplies as well, average flows alone tell only part of the picture.  Global warming is anticipated to produce more extreme weather events, ranging from floods caused by “atmospheric rivers” to more droughts.  Growing evidence suggests that we are already seeing more extreme weather events around the globe.

Sacramento River Basin Percentage of Years.png

The UC Davis study cited above also shows this change in weather extremes.  As summarized in the table above, this analysis concludes that by the end of the century, the occurrence of dry and critically dry years could increase dramatically.  This effort includes two carbon emissions scenarios, a more severe A2 emissions scenario and a more moderate B1 scenario.  UC Davis’ analysis of these scenarios suggests that dry and critically dry years, which represent 16.4 to 18.3 percent of all years today in the Sacramento River Basin, could increase to 34.1 to 37.8 percent by 2051-2100.   This projected doubling of drier years has profound implications for the reliability of future water supplies.  This analysis also concluded that the percentage of wet years may fall from 37.7-39.3 percent today to 28.2-30.6 percent by the end of the century.  In the Delta, this trend will increase the water challenges facing the ecosystem and water users alike.  In short, we may face fewer opportunities for a “big gulp” in the Delta and the need to plan for more “little sips.”

  • Portfolio-Based Solutions:  As described above, investments in local water sources that are less vulnerable to climatic extremes can increase the reliability of our water supplies. And added storage in places like urban Southern California can provide greater water supply buffers to prepare us for more dry years and longer droughts.                                                                             

Impacts on Fish. Rising temperatures and changing runoff patterns will also stress the Bay-Delta’s fish and wildlife, particularly cold water species like steelhead and commercially important Chinook salmon. These species are struggling today, in an ecosystem that has experienced an unprecedented decline in the past decade.     

  • Portfolio-Based Solutions:  This new approach would help increase the climate resilience of the Bay-Delta ecosystem in many ways.  First, by strengthening flow and pumping rules to reflect the best science we have today, this portfolio would help reverse the decline in recent years that has left Bay-Delta species so vulnerable. Habitat restoration, particularly flood plain restoration, can also significantly benefit salmon and improve their survival in the ocean.  And by investing in local water supplies and South of Delta storage, this approach would significantly reduce pressure for water diversions in a growing number of dry years and in seasons such as the spring and fall, when fish and wildlife are most vulnerable.  By restoring a healthier ecosystem and reducing water demand at critical times, the portfolio approach can help give the Bay-Delta a fighting chance in the future.

There is no single silver bullet to meet our water needs and prepare for climate change impacts in the Bay-Delta, but as water policy veteran Sunne McPeak said years ago, what we need is a “silver buckshot” approach.  The new portfolio-based conceptual alternative must be analyzed and refined, but it provides a template for a Bay-Delta plan that can meet human and environmental needs today, while preparing us to face the challenges posed by global warming.

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