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Water: Impacts, Risks, and Adaptation 205Sacramento-San Joaquin Bay Delta VulnerabilitiesBox 10.2 (Continued)In addition to its physical vulnerabilities, thedelta also is home to several threatened and endangeredspecies and many invasive species.To protect endangered species, the cross-deltapumps have been shut down for short periods inrecent years by federal court order (NRC 2010).A $11 billion bond issue has been proposed tobuild a canal around the periphery of the delta buthas not yet been put on the ballot in part due toCalifornia’s continuing budgetary problems anddisputes over the impacts of the canal. In 1982, asimilar peripheral canal was heavily rejected byvoters (Orlob 1982; Hundley 2001).Besides its vulnerable water infrastructure,the delta is traversed by other key infrastructureincluding major north-south and east-west highways,electrical power lines, gas lines, and raillines, all of which are threatened by flooding fromthe two rivers and by sea-level rise (Lund et al.2010).All of these factors have created a contentioussituation. Over the last ten years, federal, state,municipal, agricultural, and environmental interestshave engaged in a variety of complex andexpensive stakeholder initiatives in an attempt tocreate solutions acceptable to all parties (Owen2007; Isenberg et al. 2007; Isenberg et al. 2008).10.4 Water Sector Adaptation ActivitiesFederal, state, regional, and municipal water management entities over the last fiveyears or so have made substantial investments to understand the physical impacts towater supplies under a changing climate. Additional but more limited work has focusedon societal vulnerabilities to these impacts. Many supply-side and demand-sideadaptation strategies and solutions are now being considered. The principal challengesand barriers to climate-change adaptation include (1) uncertain, rapidly moving, and,in some cases, contentious scientific studies, and (2) physical, legal, and institutionalconstraints on strategies and solutions. Adaptation strategies and solutions are generallyvery specific to a region, limiting widespread application. Twentieth-century waterplanning was based in part on the idea that climatic conditions of the past would be representativeof those in the future; but this model is much less useful in the twenty-firstcentury. Reservoir size, flood control operations, and system yield calculations were allpredicated on this important concept, known as stationarity. Replacing this fundamentalplanning model, or paradigm, is proving to be extremely difficult (Milly et al. 2008;Barsugli et al. 2009; CDWR 2009a; Brown 2010). The unreliability of regional projectionshas hindered planning efforts; water managers cannot simply replace historical flowsequences in their planning models with projected flows (Kerr 2011b). The rest of thissection describes the various adaptation activities being pursued by water managers inthe Southwest.