Urban metabolism: A review with reference to Cape Town
Improved sustainability of cities requires equitably distributed and ecologically safe, if not restorative, infrastructure systems, as well as reduced reliance on resources from beyond urban boundaries. To shape infrastructure systems in a sustainable and equitable manner, knowledge about the sources and demands of the resources they convey is necessary, as well as the technologies which ensure their efficient use and safe return to the environment. This paper undertakes a basic urban metabolism assessment to examine resource consumption in the City of Cape Town. It examines the type and quantity of resources which fuel the city and its people, in order to highlight prospects for the sustainability of Cape Town. Key findings from resource profiles of Cape Town show that annual energy and water consumption, which are feared to be approaching system limits, have actually shown decline in consumption since 2007 and 2011 respectively. The key intervention to reduce energy consumption and resultant carbon emissions lies in reducing low-occupancy private car usage, while the key limitations to reducing raw water abstraction through wastewater reuse is the limited ability to store and redistribute it. Comparing maps of resource access to maps of material stocks shows that while the city periphery experiences low resource access, resource stocks are potentially quite dense. The spatial location of resource stock, flow and consumption represents a useful tool for detailed urban planning and service delivery, and is a gap in need of researching. Although flows of food are difficult to track, estimates suggest that 11.6% of the food processed in Cape Town is grown within municipal boundaries and interventions for keeping nutrients in the system should be explored. Examining the flow of people between suburbs over time shows that migration dynamics are entrenching poverty in already high poverty suburbs, as people with economic means are more likely to move to better serviced suburbs than invest in their current ones. This presents a need for the city to invest in these underserviced areas, so as to retain personal investment. Key recommendations for urban and resource planning are the integrated analysis of resource nexuses using system dynamics modelling, as well as integrating departments within the municipality, to enable more holistic intervention strategies. To aid this, research into a baseline examination of differential spatial and temporal flows of resources at suburb level is currently underway.