The vulnerability and resilience of a city's water footprint: The case of Flagstaff, Arizona, USA

Abstract

Research has yet to operationalize water footprint information for urban water policy and planning to reduce vulnerability and increase resilience to water scarcity. Using a county‐level database of the U.S. hydro‐economy, NWED, we spatially mapped and analyzed the Water Footprint of Flagstaff, Arizona, a small city. Virtual water inflow and outflow networks were developed using the flow of commodities into and out of the city. The power law distribution of virtual water trade volume between Flagstaff and its county trading partners broke at a spatial distance of roughly 2000 km. Most large trading partners are within this geographical distance, and this distance is an objective definition for Flagstaff's zone of indirect hydro‐economic influence—that is, its water resource hinterland. Metrics were developed to measure Flagstaff's reliance on virtual water resources, versus direct use of local physical water resources. Flagstaff's reliance on external water supplies via virtual water trade increases both its hydro‐economic resilience and vulnerability to water scarcity. These methods empower city managers to operationalize the city's Water Footprint information to reduce vulnerability, increase resilience, and optimally balance the allocation of local physical water supplies with the outsourcing of some water uses via the virtual water supply chain.

Global virtual water trade and the hydrological cycle: patterns, drivers, and socio-environmental impacts

“…Most studies on VW trade quantify international flows with commodity group resolution typically VW trade estimates that are highly resolved in space provide the greatest opportunity to evaluate links between water scarcity, water resources sustainability, and complex supply chains (Flach et al 2016). For example, VWT resolved to the urban spatial scale enables the quantification of exposure and resilience of cities to direct and indirect water stress (Rushforth and Ruddell 2016). There is significant potential to evaluate high spatial resolution VWT within the US, due to the availability of sub-national empirical transfers (e.g.…”

“…FAOSTAT, COMTRADE) and the paucity of detailed sub-national trade data is a major limiting factor. Sub-national VW trade studies typically pair VWC with modeled estimates of sub-national commodity transfers (e.g Verma et al 2009, Zhang and Anadon 2014, Dalin et al 2014, Rushforth and Ruddell 2016. or MRIO models (Guan and Hubacek 2007, Dong et al 2014, Zhang and Anadon 2014, Deng et al 2016a, Serrano et al 2016, Ren et al 2018).…”

Prediction in a socio-hydrological world

“…Konar et al 2011), partly constrained by data availability. However, recent research has begun to evaluate sub-national virtual water transfers (Dalin et al 2014, Dang et al 2015, including those to and from cities (Rushforth and Ruddell 2016), and these studies suggest that hydrological units such as the basin may not always be the appropriate scale at which analysis/prediction is possible. On the one hand, local water scarcity may not significantly impact global markets unless the region contributes to a substantial fraction of global production.…”

Direct and indirect urban water footprints of the United States

“…A component of indirect water flows, virtual water flows, account for a large volume of water embedded in the food products, fuel resources, and other processed goods that enter an urban environment [ Rushforth and Ruddell , ]. The embedded water in these resources carries important implications for food and water security [ Hoekstra and Chapagain , ; Porkka et al ., ].…”