Resilience Dynamics of Urban Water Supply Security and Potential of Tipping Points

Abstract

Cities are the drivers of socioeconomic innovation and are also forced to address the accelerating risk of failure in providing essential services such as water supply today and in the future. Here, we investigate the resilience of urban water supply security, which is defined in terms of the services that citizens receive. The resilience of services is determined by the availability and robustness of critical system elements or “capitals” (water resources, infrastructure, finances, management efficacy, and community adaptation). We translate quantitative information about this portfolio of capitals from seven contrasting cities on four continents into parameters of a coupled system dynamics model. Water services are disrupted by recurring stochastic shocks, and we simulate the dynamics of impact and recovery cycles. Resilience emerges under various constraints, expressed in terms of each city's capital portfolio. Systematic assessment of the parameter space produces the urban water resilience landscape, and we determine the position of each city along a continuous gradient from water insecure and nonresilient to secure and resilient systems. In several cities stochastic disturbance regimes challenge steady‐state conditions and drive system collapse. While water insecure and nonresilient cities risk being pushed into a poverty trap, cities which have developed excess capitals risk being trapped in rigidity and crossing a tipping point from high to low services and collapse. Where public services are insufficient, community adaptation improves water security and resilience to varying degrees. Our results highlight the need for resilience thinking in the governance of urban water systems under global change pressures.

Balancing security, resilience, and sustainability of urban water supply systems in a desirable operating space

“…These operating spaces are constrained by minima of SRS needed for maintaining system functions as shown in figure 1. In our earlier work, we found the lower boundaries for security and resilience, where only a fraction of residents received services, and UWSS had a high likelihood of collapse [20,21]. We evaluate here the minimum constraints for sustainability.…”

“…Persistence during and recovery from shocks requires buffering capacity, e.g. water drawn from diverse sources during a drought, often from beyond the local system boundaries, and which are allowed to replenish in the absence of shocks [20,21]. This stretches the spatial and temporal scales of resilience and requires the consideration of additional inter-sector dependencies.…”

“…The resilience of UWSS was quantified using a systems dynamics model (see details in [21]), which determines stable system states and simulates times series of recurring stochastic shocks, resulting in supply service deficits and management response to recover services. Parameters in the model were derived from the CPA, as explained in table S.3 (SI).…”

“…To disentangle these dimensions, we present an integrated quantitative framework with distinct definitions for security, resilience, and sustainability. We employ the Capital Portfolio Approach (CPA) developed for quantifying security and resilience [20,21], and we add here another dimension to the framework to quantify local and global sustainability of UWSS. Our analysis is guided by the proposition that the way in which system functions are achieved determines its sustainability.…”

“…As the third in a trilogy of papers, we apply the new framework to assess local and global sustainability of UWSS of seven diverse cities, whose security and resilience have been investigated previously [20,21]. We compare results across these diverse cities to understand trends in SRS, and integrate the three concepts to analyze their balance.…”