Cities as ecosystems: functional similarities and the quest for sustainability

Ecosystems and urban systems share similarities. To grasp them we exploit the ecosystem nature of cities by applying ecological network analysis to three urban systems represented as water flow networks. Urban expansion may bring about transformations that are coherent with ecosystem development. Trends predicted in ecosystems as for entropy, flow diversity, conservation of medium, information, niche specialization, seem to hold also in the urban context. By contrasting the three urban networks with alternative configurations of their flow structure inspired by sustainability thinking we highlight that single-issue criteria that commonly direct actions toward sustainability may have unexpected effects at the whole system scale.