Sustainable Water and Environmental Management in the California Bay-Delta (2012) / Chapter Skim
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4 Environmental Change: Challenges and Opportunities
4 Environmental Change: Challenges and Opportunities
Pages 153-190
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From page 153... ...
Some of the primary challenges include, but are not limited to, habitat loss, climate change including sea level rise, and levee stability. In this chapter, we discuss the details and the potential implications of these challenges and opportunities.
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From page 154... ...
. Thus, all aspects of the delta, past and present, serve as habitat and all the environmental changes described in Chapters 1 and 3 affect habitat and the species that depend on it.
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From page 155... ...
. Even if tidal water and dredged material were reintroduced to flooded islands to return them to an intertidal or shallow subtidal elevation, continued maintenance of such elevations in the face of sea level rise will be necessary to maintain native wetland plant communities within their hydrologic tolerance limits and will require the accumulation of organic matter and sediment.
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From page 156... ...
. However, only a few projections have quantified the impacts of warming, consequent changes in hydrology, and the sea level rise on the ecology of the Central Valleybaydelta region.
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From page 157... ...
, is the primary change in climate and the cause of sea level rise in the Central Valley. The other primary driver, natural variability, is manifested in multidecadal changes in precipitation and temperature patterns (Pagano and Garen 2005)
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From page 158... ...
. During the 20th century, the global mean sea level rise has been estimated to be about 1.7 mm/yr (Church and White 2011)
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From page 159... ...
suggest that the global mean sea level rise may be as much as 1.4 m or more (Pfeffer et al. 2008, Vermeer and Rahmstorf 2009)
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The changes in hydrology described above would pose significant challenges for the management of the water resources systems such as the Central Valley Project (CVP) and the State Water Project (SWP)
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From page 161... ...
. problem of declining groundwater levels in the Central Valley (Famiglietti et al.
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From page 162... ...
. The frequency of levee failure is likely to increase in the future with potential increases of flood flows from the upstream reservoirs as a result of timing change in runoff and increased water levels in the delta conveyance canals due to sea level rise.
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From page 163... ...
On the basis of this model, Wagner et al. argue that the effects of flow are generally small and are confined to shorter time scales, and so could be ne FIGURE 4-1 Suisun Bay delta water temperature for the period 2000-2006.
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From page 164... ...
. In the Central Valley, summer water temperature regularly exceeds salmons' threshold (Figure 4-2B)
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From page 165... ...
. How climate change will affect these 15 windows is highly relevant in the rehabilitation of Central Valley salmon and steelhead.
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From page 166... ...
. Expanding the duration of high temperature would narrow the window in which fall Chinook runs could occupy the Central Valley, which would disrupt both their growth pattern and migration timing.
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From page 167... ...
. Such evolutionary-scale focuses are highly relevant to the long-term effects of climate change on fish, but the more immediate issue, especially for the Central Valley, which is the southern end of the salmonid range, is the impact of extreme events such as heat waves and multiyear droughts.
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From page 168... ...
. Managing Temperature From the perspective of water resources management, it does not appear that the increasing delta water temperatures can be efficiently mitigated by project and reservoir operations.
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From page 169... ...
Integrating the Analyses The preceding discussion suggests that many variables and factors need to be considered in projecting the effects of climate change on the Central Valley system. In such a situation, an integrated analysis using a series of linked models would be required to understand the cascading effects and the feedbacks on the large water resources system, including the delta.
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From page 170... ...
170 SUSTAINABLE WATER MANAGEMENT IN THE DELTA FIGURE 4-3Projected 2010-2099 changes in selected environmental indicators expressed as median trend per decade for two climate scenarios (red and blue)
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From page 171... ...
Yet if the climate predictions are correct, frequent extreme events will increase the need for Central Valley water resources by both the ecosystem and the public. In this case, managers may be asked to consider hard choices that are more in the context of triage than rehabilitation (e.g., CASCaDE 2010, Hanak et al.
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From page 172... ...
Groundwater storage with artificial recharge, particularly in the Central Valley south of the delta, should be considered, along with opportunities to increase reservoir storage in the system or to change the operating rules for existing systems. The expansion of storage should not come at the expense of negative environmental impacts, and comprehensive planning investigations will be needed to explore this option (MedellinAzuara et al.
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From page 173... ...
The 0.2-m rise of San Francisco Bay during the 20th century did not require large additional flood protection works. However, if the 21st century should see a significant increase in this trend, major investments will be needed in the bay delta to mitigate the broader impacts of climate change.
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From page 174... ...
Beginning with the 1986 flooding in the Central Valley, followed by major levee failure in the 1993 Missouri River floods (Tobin 1995) , through levee failures at Mildred Island in 1983, Liberty Island in 1998, and Lower Jones Tract levee in 2004, and with catastrophic breaches in New Orleans during Hurricane Katrina in 2005, the science and engineering around levees is increasingly under scrutiny at the local and national levels.
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From page 175... ...
. As politicians, scientists, and engineers look toward more sustainable water management in the delta, the instability and interdependence of levees is likely to be a chokepoint for achieving any measure of water-supply reliability or ecosystem recovery.
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From page 176... ...
severely constrain the hydrology and resulting habitat types are likely not to maintain their benefit over the long-term as levees fail, sea level rises, and upstream hydrology changes.
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From page 177... ...
It will provide for some recreation and it will continue to provide some ecosystem services. And it, like all ecosystems, will continue to respond to environmental changes.
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From page 178... ...
With respect to the delta ecosystem, building habitat or restoring flows does not mean "they will come." Together the experiences from studies of change in ecosystems around the world suggest the importance of considering both alternate states and hysteresis in visions for a future delta. However, the presence of substantial biotic and abiotic changes, together with the potential for alternative stable states, does not mean that we cannot effect changes to yield a more desired delta ecosystem.
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From page 179... ...
Indeed, ensuring ecosystems that are resilient in part relies on maintaining resilience at the individual species level. Maintaining genetic diversity within individual populations increases the likelihood that the population will be sustained in the face of environmental change -- a point recognized in recent hatchery and recovery plans for salmon by the National Marine Fisheries Service (NMFS)
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From page 180... ...
Projected increases in the mean sea level and the extremes have the potential to increase the frequency of levee failures and inundation of islands, particularly if upstream floods, astronomical tides, and winter storms coincide in the future when the mean sea level has increased due to warming. Sea level rise also has the potential to increase saltwater intrusion and degrade water quality with a significant impact on water exports.
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From page 181... ...
They also would include adoption of measures designed to mitigate water temperature increases that are harmful to fish species. The instability and interdependence of levees are likely to be major issues for achieving any measure of water-supply reliability or ecosystem rehabilitation.
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2008. Levee failures and social vulnerability in the Sacramento-San Joaquin delta area, California.
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2009. Climate Change Scenarios and Sea Level Rise Estimates forthe California 2009 Climate Change Scenarios Assessment.
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2011. Satellites measure recent rates of groundwa ter depletion in California's Central Valley.
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2009. The Impacts of Sea-Level Rise on the California Coast.
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2006. Historical population structure of Central Valley steelhead and its alteration by dams.
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2009. Biological Opinion on the Long-Term Central Valley Project and State Water Project Operations Criteria and Plan.
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2008. Kinematic constraints on glacier contributions to 21st century sea-level rise.
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Sensitivity of Future Central Valley Project and State Water Project Operations to Potential Climate Change and Associated Sea Level Rise, OCAP-BA, July.
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2006. Central Valley salmon: A perspective on Chinook and steelhead in the Central Valley of California.
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