Publications
Urban Social-Ecological-Technical Systems
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Published in Environmental Research Letters, 2022
Urbanization and competing water demand, as well as rising temperatures and changing weather patterns, are manifesting as gradual processes that increasingly challenge urban water supply security. Cities are also threatened by acute risks arising at the intersection of aging infrastructure, entrenched institutions, and the increasing occurrence of extreme weather events. To better understand these multi-layered, interacting challenges of providing urban water supply for all, while being prepared to deal with recurring shocks, we present an integrated analysis of water supply security in New York City and its resilience to acute shocks and chronic disturbances. We apply a revised version of a recently developed, quantitative framework ('Capital Portfolio Approach', CPA) that takes a social-ecological-technological systems perspective to assess urban water supply security as the performance of water services at the household scale. Using the parameters of the CPA as input, we use a coupled systems dynamics model to investigate the dynamics of services in response to shocks—under current conditions and in a scenario of increasing shock occurrence and a loss of system robustness. We find water supply security to be high and current response to shocks to be resilient thanks to past shock experiences. However, we identify a number of risks and vulnerability issues that, if unaddressed, might significantly impact the city's water services in the mid-term future. Our findings have relevance to cities around the world, and raise questions for research about how security and resilience can and should be maintained in the future.
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[11] Governing Sustainable Transformations of Urban Social-Ecological-Technological Systems
Published in npj Urban Sustainability, 2022
Cities have grown rapidly—while they provide opportunities for many, they must also confront pervasive and rising inequality, unsustainable consumption, and growing vulnerability to the impacts of climate change. Recent research emphasizes the need to improve urban resilience and sustainability in the face of climate change, but offers circumscribed approaches that mostly focus on either 1) resource management and service provision, 2) social processes and capacities for transformation, or 3) governance and power relations among actors. Here, we embrace the emerging approach that considers urban areas as interdependent social-ecological-technological systems (SETS) and consider the implications for sustainable service provision; the role of bottom-up efforts in initiating urban transformations; and how governance may, under certain conditions, coordinate these efforts to effect broader change.
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The three papers below are part of a "trilogy". The first introduces an integrated approach (Capital Portfolio Approach, CPA) for quantifying the security of urban water supply services [3]. The second translates the CPA into parameters of a model that simulates the resilience dynamics of water supply services [2]. The third expands on the CPA method to investigate the sustainable governance of urban water supply system security and resilience, and the balance of security, resilience, and sustainability in their local and global contexts [1]. All three papers use data for the same seven global cities. They are the main body of work carried out as part of my PhD. The dissertation takes a much broader view of global urban water supply issues [4].
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Published in Environmental Research Letters, 2020
We quantify the sustainability of urban water supply systems (UWSS) based on the performance of local sustainable governance and the magnitude of global water and ecological impacts. We develop a new framework that integrates security, resilience, and sustainability to investigate trade-offs between these three distinct and inter-related dimensions. We apply the new framework to seven cities selected from diverse hydro-climatic and socio-economic settings on four continents. We find that UWSS security, resilience, and local sustainability coevolve, while global sustainability correlates negatively with security. Therefore, under current governance paradigms, cities that establish increasing security goals also increase global impacts, which may turn out to be infeasible in the long-term as global change impacts (e.g., sealevel rise) become more pressing. Beyond local adaptation and short-term system resilience, long-term perspectives of transformation will be critical for balancing security, resilience, and local and global sustainability. Balance is described by the desirable operating space, where urban services are not just secure and resilient, but also locally and globally sustainable.
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Citation: Krueger E, Borchardt D, Jawitz JW, Rao PSC (2020): Balancing Security, Resilience, and Sustainability of Urban Water Supply Services in a Desirable Operating Space. Environmental Research Letters, 15 (3), https://doi.org/10.1088/1748-9326/ab6c2d.
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[9] Resilience Dynamics of Urban Water Supply Security and Potential of Tipping Points
Published in Earth's Future, 2019
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We show the dynamic behavior of urban water supply services in response to recurring, stochastic shocks. We use a dynamical systems model that is parameterized using empirical data of urban water supply systems in seven diverse cities. While we find a single stable state for each of these systems, recurring shocks can lead to system failure in several of these cities, and the potential for tipping points exists for cities with excess capital availability and loss of robustness. Stable system states and resilience dynamics are improved by community adaptation to insecure water services, but recurring large shocks erode community adaptive capacity, which leads to a loss of resilience.
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[8] Quantifying Urban Water Supply Security Under Global Change
Published in Global Environmental Change, 2019
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We propose a new method for quantifying urban water supply security, which is defined here as the level of supply services that citizens receive. We integrate water resource availability, the state of distribution infrastructure, financial capital, and the efficacy of urban water management to quantify the services provided by an urban entity ("public services"). As in many cases public services do not meet demand, we also quantify community adaptation to measure additional services (privately accessed water volumes, in-house treatment and storage, etc.). This holistic method allows the quantification of urban water supply security for cities across the world and comparison of service constraints and adaptive capacity in both advanced and developing economies. We present and compare results for seven cities: Chennai (India), Ulaanbaatar (Mongolia), Mexico City (Mexico), Amman (Jordan), Melbourne (Australia), Berlin (Germany), and Singapore.
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Published online through Purdue University, 2019 (Dissertation)
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In my dissertation I investigated the concepts of security, resilience, and sustainability with respect to urban water supply. Different approaches are explored to understand these concepts both from a comparative perspective of urban water supply security across the globe, and from a case study perspective in the seven cities (Amman, Chennai, Mexico City, Ulaanbaatar, Melbourne, Berlin, Singapore), as well as inequalities of water supply within these cities. The approaches are taken from hydrology and engineering, social-ecological and complex systems, and network theory, and I used narratives to provide context that describes the case studies beyond the data.
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Complex network analysis / urban infrastructure
The group of articles below investigates the functional topologies of urban infrastructure networks (water supply, sanitary sewers/drainage, roads) and compares these to the characteristics of natural networks (e.g., river networks). This work was initiated through a series of Network Synthesis Workshops, and carried out by their participants who first met at the first workshop of this series at Korea University in 2015.
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Published in World Environmental and Water Resources Congress, 2019
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We investigate the robustness of urban water distribution networks to failure based on isolation valve placement in two urban systems. We analyze robustness using the dual representation of these networks that reveal the functional hierarchy of the distribution pipes. We compare the network characteristics (e.g., node-degree distributions, modularity, path length, assortativity) of the two urban systems and find differences in network robustness that is mainly driven by isolation valve density.
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Citation: Zischg J, Reyes-Silva JD, Klinkhamer C, Krueger E, Krebs P, Rao PSC, Sitzenfrei R, 2019: Complex Network Analysis of Water Distribution Systems in Their Dual Representation Using Isolation Valve Information. World Environmental and Water Resources Congress, 484-497.
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[5] Topological convergence of urban infrastructure networks
Published as pre-print on arXiv, 2019
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We apply complex network analysis to 125 urban infrastructure networks (roads, water distribution, drainage) of varying sizes to show similarity in their functional topologies. We convert the graphs of these networks into the information space ("dual mapping"), which uses their functional hierarchy to inform the creation of graph nodes and links. Node-degree distributions of all 125 networks are approximated by power-law functions that converge towards a narrow range of power-law exponents (γ=2.49). This indicates universal scaling laws for urban infrastructure networks, similar to those found for natural networks.
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[4] Functional Topology of Evolving Urban Drainage Networks
Published in Water Resources Research, 2017
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We compare the scaling characteristics of urban drainage networks and those of river networks using Hack's law of length-area scaling, and exceedence probability of distribution of upstream contributing area. In spite of engineering design, urban drainage networks evolve into scale-invariant networks with similar power-law scaling to that of river networks.
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Citation: Yang S, Paik K, McGrath G, Urich C, Krueger E, Kumar P, Rao PSC, 2017: Functional Topology of Evolving Urban Drainage Networks. Water Resources Research, 53.
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[3] Evolution of Complex Network Topologies in Urban Water Infrastructure
Published in World Environmental and Water Resources Congress, 2017
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We assess the historical development of the urban water distribution and drainage networks (WDN and UDN) of a small European city by investigating the topologies of these complex networks. We use the dual representation of the network, which considers pipes as nodes and intersections as edges. We observe scale-free network characteristics which evolve with consistent patterns over time. We present the remapping of the dual network attributes to the spatial map, which allows investigating the spatial effect (e.g., affected neighborhoods or number of affected customers) of vulnerabilities identified through the complex network analyses using dual representation.
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[2] Generic patterns in the evolution of urban water networks: Evidence from a large Asian city
Published in Physical Review E, 2017
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We examine high-resolution data for the water distribution and sanitary sewer networks (WDN and SSN) in a large Asian city. We spatially disaggregated WDN and SSN into functional subnets to examine intracity topological differences, and time-stamped SSN data were used to understand network evolution over several decades as the city expanded. We generated graphs using a dual-mapping technique (Hierarchical Intersection Continuity Negotiation), which emphasizes the functional attributes of these networks. A double Pareto (power-law) model approximates the node-degree distributions of both water infrastructure networks across spatial and hierarchical scales, and throughout their temporal evolution. These results indicate that generic mechanisms govern the networks’ evolution similar to those of scale-free networks found in nature. Deviations from the general topological patterns are indicative of (1) incomplete establishment of network hierarchies and functional network evolution, (2) capacity for growth (expansion) or densification (e.g., in-fill), and (3) likely network vulnerabilities.
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Other articles
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Resilient urban infrastructure?
Published in Decision Analysis Today, 2017
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This article reflects on the role of adaptive capacity for resilience - in the face of multiple hurricanes hitting the Southern United States in 2017.
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Aligning Different Schools of Thought on Resilience of Complex Systems and Networks
Book chapter published in IRGC Resource Guide on Resilience, 2016
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This chapter reflects on the different concepts of resilience that have been developed in ecology and social-ecological systems, engineering and safety management, control theory, and spatial resilience as developed in the fields of geomorphology, landscape ecology, and complex network studies. Approaches to designing resilience have largely relied on robustness, resistance, and redundancy of built components, while a quantification of resilience is only possible after failure occurred and recovery was (or was not) successful. However, crucial aspects of resilience, such as adaptation and transformation rely on people's adaptive capacity, which should be a principle component of future quantitative measures of the resilience of coupled human-engineered systems.
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For more see Full CV and Google Scholar.