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364 assessment of climate change in the southwest united statesCase Study 4: Collaboration to Protect the Tijuana EstuaryBox 16.4The Tijuana River Estuary is the largest and oneof the last remaining large tidal wetlands on thePacific Coast (Roullard 2005, plates 31-36; Ganster2010). The 2,500-acre (1,012-hectare) Tijuana RiverNational Estuarine Research Reserve (TRNERR)is situated on the international boundary at theendpoint of the 1,750-square-mile (4,532 squarekilometer) binational Tijuana River Watershed.One-third of the watershed is in the United Statesand the remaining area in Mexico, and includesmuch of the rapidly urbanizing areas of Tijuanaand Tecate. The estuary’s diverse contiguousbeach, dune, salt marsh, riparian, and uplandhabitats are home to many rare and endangeredspecies of plants and animals. The estuary is vulnerableto human impacts and the effects of climatechange that include sea-level rise, alteredprecipitation patterns and sedimentation rates,and invasion of exotic species. The likely effectsof climate change also pose significant challengesto the viability of past habitat restoration effortsin the estuary (see, for example, Zedler 2001).In order to make this system more resilientto both watershed and coastal stressors, the TijuanaRiver Valley Recovery Team was convenedin 2008. xl This effort brings together over thirtyregulatory, funding, and administrative agencieswith the scientific community, environmentalgroups, and other stakeholders. The RecoveryTeam has produced a “roadmap” that addressesbroad ecosystem goals and identifies actions thatcan facilitate adaptation to climate change, suchas controlling cross-border flows of sedimentand trash, improving hydrology, changing landuse, and restoring habitat (Tijuana River ValleyRecovery Team 2012). The plan identifies broadzones of the Tijuana River estuary area that willserve different functions. These include (1) transitionalareas designed to accommodate habitatshifts associated with rising sea level, (2) privatelands that should be acquired and restored tohabitats that can dynamically respond to changingconditions, and (3) lands that will remain inagricultural or recreational use and are protectedinundation. The roadmap also specifically callsfor the impacts of climate change to be assessedat more precise spatial scales and shorter timescales so that management practices can effectivelyrespond to evolving climate conditions.energy provision during peak demand; extended and more severe drought periods; andhigher evapotranspiration rates (Table 16.1). As Udall (2011, 12) notes, “The past centuryis no longer a guide to water management” (see also Planning Techniques and Stationaritysection, Chapter 10). The principal watersheds in the region are of particular significanceto the sustainability of ecosystems and human activities.The two major transboundary rivers in the border region—the Colorado River andthe Rio Grande—are systems where conflicts over water are prevalent (see Chapter 10,Box 10.1). Both the United States and Mexico have aging water infrastructures with avoluminous backlog of needs that are very expensive to fix. As described throughoutthe present work, water is connected to many other sectors, including energy, transportation,human health, ecosystems, and agriculture. Higher projected temperatures willaffect water quality; surface water temperatures are expected to increase, in turn impactingthe organisms and species (including humans) that depend on these resources,