From fail-safe to safe-to-fail: sustainability and resilience in the new urban world

The extent to which the 21st Century world will be "sustainable" depends in large part on the sustainability of cities. Early ideas on implementing sustainability focused on concepts of achieving stability, practicing effective management and the control of change and growth-a "fail-safe" mentality. More recent thinking about change, disturbance, uncertainty, and adaptability is fundamental to the emerging science of resilience, the capacity of systems to reorganize and recover from change and disturbance without changing to other states-in other words, systems that are "safe to fail." While the concept of resilience is intellectually intriguing, it remains largely unpracticed in contemporary urban planning and design. This essay discusses the theory of resilience as it applies to urban conditions, and offers a suite of strategies intended to build urban resilience capacity: multifunctionality, redundancy and modularization, (bio and social) diversity, multi-scale networks and connectivity, and adaptive planning and design. The strategies are discussed in the context of resilience theory and sustainability science, and are illustrated with innovative policies, projects, and programs selected from international examples. 1. The new urban world Sometime in the year 2007, demographers estimated that global population became predominately urban for the first time in history. Estimates from multiple sources including the United Nations predict this trend to continue throughout this century, with the world’s population reaching 70% urban by 2050. These global data mask significant differences in urban population trends between the developed and the developing world – where much of the increase in urban inhabitants will occur. Despite these regional differences, the world is undeniably becoming more urban – with profound impacts on land use, human welfare, social equity and sustainability, broadly defined. Therefore, the challenge for sustainability in the 21st Century will, arguably, be won or lost in cities and their larger urban regions. 2. Sustainability, equilibrium and resilience Expect the best, plan for the worst, and prepare to be surprised‖ --Denis Waitley The modern era of the 20th century was arguably associated with an equilibrium, or deterministic conception of nature, science and ecology. Developed societies embraced a ―fail safe‖ mentality based on the promise of science and technology to meet social and economic needs, cure disease, and undo the environmental mistakes of previous generations. In the latter half of the 20th century, more-or-less coincident with the advent of