Research Publications

Over half of the world’s population now lives in cities and this figure may reach 60% by 2030. Although urban centers have become a primary driver of resource consumption and waste production, they are also key leverage points in our efforts to foster a sustainable society. Engineering research has conceptualized and modeled cities as an organismic metabolism, consuming energy and materials, metabolizing them, and generating emissions and waste. But through this material and energy flow analysis, the specific complex interactions between infrastructure systems that shape these flows remain poorly understood. In fact, the urban metabolism analogy often obscures the critical processes because unlike organisms (but like ecosystems), cities are complex systems that are not under central control, have no true equilibrium state, and do not have a particular developmental end point. Understanding the city as ecosystem requires knowledge of how human and natural infrastructure systems interact to create the emergent properties. This includes engineering infrastructure systems and their cointeraction (e.g., water−energy nexus), but also a variety of other “infrastructures”, including ecological infrastructure, information and communications technology (ICT) infrastructure, socio-economic infrastructure (e.g., banking, finance) and social network infrastructure. Understanding how these infrastructures interact with each other and how citylevel properties emerge from such underlying interactions is fundamental to the design, development, and operation of sustainable urban systems.

Recently, ecological hierarchy theory has been applied to cities, leading to some striking observations and new models. Like ecosystems, different mechanisms may govern interactions across different scales within cities, to confer resilience and adaptability. Whereas analogies to ecosystems have guided analysis, in very few cases have ecological principles been used to provide an understanding of the potential mechanisms. For instance, although food web models have been used to trace material and energy flows among components within cities, principles that relate to how food web architecture scales with size have not been applied or examined. Similarly, stability and resilience of ecological food webs are related to specific ecological mechanisms, which also have not been examined for urban infrastructure.

Evidence thus suggests analogies to ecological systems may reveal new ways to analyze urban systems and provide design and decision guidelines for sustainable cities. We propose the concept of inf rastructure ecology as a way to analyze, via analogical mapping of urban to natural systems, the complex interdependence of urban infrastructure systems, as broadly conceived above.