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84 4 Emergent Properties in Coupled Human-Natural Systems Urban ecosystems are qualitatively distinct from other environments. In such systems, change and evolution are governed by complex interactions among ecological and social drivers. In this chapter, I investigate the emergent properties that characterize urban ecosystems by focusing on patterns (e.g., sprawl), processes (e.g., hydrology), and functions (e.g., flood regulation). I develop an analytic approach to examine complex interactions between slow and fast variables that control critical transitions, regime shifts, resilience, and innovation. I articulate formal hypotheses regarding relationships between emergent properties of hybrid ecosystems and their abilities to adapt and innovate. Uncertain future interactions between social and ecological dynamics call for a paradigm shift in urban design and planning. Emergent Properties of Urban Ecosystems Urban ecosystems are highly complex. They are hybrid, open, nonlinear, unpredictable, and are characterized by multiple equilibria (Folke et al. 2002; Gunderson and Holling 2002; Hartvigsen, Kinzig, and Peterson 1998; Levin 1998; Portugali 2000). Hybrid ecosystems are characterized by complex interactions, emergent properties, and dissipative thermodynamics (Nicolis and Prigogine 1977). At higher levels, patterns emerge from the local dynamics of multiple agents interacting among themselves and with their environment. Sprawl is an example of an emergent pattern of dynamic interactions among human preferences for residential location, Emergent Properties 85 individual mobility patterns, transportation infrastructure, and real estate markets, and between these factors and the regional climate, hydrology, and topography (Alberti 2008; Torrens and Alberti 2000). Households, which are themselves complex entities, compete simultaneously in the job and real estate markets when people decide where to live. Furthermore, people have preferences and evaluate trade-offs that are highly dependent on their individual characteristics (e.g., income, household size, and children) and the socioeconomic (e.g., quality of public services) and environmental (e.g., environmental amenities) attributes of potential alternative housing locations. Developers and local governments make decisions about the development of land and infrastructure. These decisions are strongly influenced by consumer preferences and housing demand and are also shaped by biophysical (e.g., topography), economic (e.g., resources), and institutional (e.g., property rights) constraints. Metropolitan patterns eventually emerge from local interactions among various agents and their decisions; in turn, these patterns affect processes that support urban ecosystem functions (e.g., mobility, air quality, natural habitat, safety, etc.). Resulting changes in urban ecosystem functions feed back into choices about households’ locations. In such systems, change and evolution emerge as various interacting agents engage in simple behaviors and as they respond to external factors . Uncertainty about future conditions is important, as any departure from past trends can affect how a system evolves. Uncertainty and the likelihood of surprise are controlled by complex interactions among ecological and social drivers and their unpredictable dynamics (Alberti 2008). Change has multiple causes, can follow multiple pathways, and is highly dependent on historical context; that is, it is path dependent (P. M. Allen and Sanglier 1978, 1979; McDonnell and Pickett 1993). Agents are autonomous and adaptive, and they change their rules of action based on new information. In urban ecosystems, feedback mechanisms that operate between ecological and human processes can amplify or dampen changes, and thus they regulate the systems’ responses to external pressures. For example, in delta regions, land-cover changes and rapid loss of tidal marshes, coupled with hydrological and ecological changes associated with the development of hard flood-control structures (e.g., dikes, dams, levees, groins, seawalls, and stormwater management mea- 86 Chapter 4 sures), make systems more vulnerable to extreme climate events and prompt increased demand for more flood-control infrastructure (box 4.1). Urban ecosystems are also highly interdependent social and ecological networks (i.e., networks of networks). In cities, built and virtual infrastructures act as networks of systems that produce and distribute a continuous flow of essential services. As in biological systems, where genetic regulatory and protein interaction networks are interdependent, so too in human systems do infrastructure networks depend on one another to function. For example, the power grid is highly dependent on communication networks for its control, but the communication network also depends on the grid for power (Parandehgheibi and Modiano 2013). Coupled human-natural systems are composed of overlapping and interdependent networks. As for ecological systems, the heterogeneity and connectivity of system components play a critical role in maintain­ ing functional systems. Increasing connectivity among people, business enter­ prises, and governmental and nongovernmental organizations around the globe enables communication, efficiency, and innovation. At the same time, this increasing interdependence may increase...


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