Understanding urban resilience with the urban systems abstraction hierarchy (USAH)

•Introduces a tool for mapping complex functions and urban interdependencies.•Functional interdependencies between system components are captured across scales.•Physical resources within a city are explicitly linked to resilience outcomes.•Interactions between shocks and stressors can aid resilience planning. The paper discusses how the Urban System Abstraction Hierarchy (USAH) can be used as an informative hazard-agnostic tool to understand interdependencies between shocks which impact tangible parts of the city system, and longer-term stressors which impact intangible outcomes of the city system. To create resilient cities, we must grapple with such complex interdependencies. Effective solutions that foster resilience require acknowledging the interplay between sectors (e.g. healthcare systems and ecosystem services), between scales (e.g. local and regional), between timeframes (e.g. immediate shocks and longer-term stresses), and between what we can and cannot see in the physical world (e.g. tangible resources and abstract purposes). These critical ‘systems thinking’ areas can be explored by mapping urban interdependencies through their functionality, rather than their geospatial connectivity. The aim of this paper is to build and validate the USAH as a resilience tool to do just this. The analysis demonstrates how the USAH tool can make interactions explicit whilst keeping urban complexity tractable. By quantifying interdependencies, fresh perspectives on urban functionality are provided. It concludes that the USAH tool fills an important gap in the resilience literature by helping to operationalise the complexity within urban systems.