Dynamics of Urban Metabolism
Fig. 1 Causal loop diagram of the drivers of residential building construction. Cycles labeled by “R” are positive (reinforcing) feedback loops; “B” indicates negative (balancing) feedback loops.
Abstract
Metabolism is a dynamic phenomenon. The word itself is based on the Greek word μεταβολη, meaning “change,” and the biological process it originally describes is a set of biochemical reactions and transformations of nutrients and energy. Urban metabolism is often reduced to a snapshot of the material stocks and flows in a city over a given time period, but this simplification tends to mask the richness and complexity of metabolic phenomena. In this project, we focus on developing an understanding of the dynamics of urban metabolism as a way to illuminate the functional relationships between physical material flows and socioeconomic behaviors of the city. In so doing, urban metabolism becomes more truthful and useful in efforts to compare global cities and also more salient to urban sustainability policymaking.
Method
The Dynamics of Urban Metabolism project is rooted in the use of System Dynamics (SD) modeling to represent and clarify the stocks, flows of resource throughput and the feedbacks, delays, and interrelationships that govern the behavior of urban metabolic systems. A highly modular and multi-scale modeling framework, SD can be used to communicate basic dynamic principles or test hypotheses of the potential responses of the system to certain detailed policy stimuli, and everything in between. A long-term goal of the project is the development of a generalized dynamic model of urban metabolism that can be adapted for any global city. In the meantime, ongoing research focuses on exploring the metabolism of urban sub-systems, such as residential housing (Davis 2012) or the water system (Noiva Welling 2011), and characterizing specific relationships between resource throughput and urban economic growth like income elasticity of consumption.
Fig. 2 Income elasticities of urban metabolic consumption in Singapore, 1962-2012. Eight metabolic flows are plotted against real (corrected for inflation) GDP on a log-log scale. Growth curves are modeled using a power law, with the exponent representing the elasticity of consumption. Income elasticity is the percent change in consumption as a result of a percent change in Singapore’s GDP.