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Creating Policy Around How Cities Outsource Water: Disaggregating Virtual Water Trade To The Watershed Level To Increase Municipal Resilience

World Water Congress 2015 Edinburgh Scotland
10. Management of water resources
Author(s): Richard Rushforth (Phoenix

Keyword(s): Sub-theme 10: Management of water resources,


Introduction: Cities are complex, coupled natural human systems that contain interacting and overlapping social, economic and environmental priorities and outcomes. For many municipal water providers, the top management priority is to secure safe and reliable water supplies year after year. Water provided by municipal providers is not just vital to human health and well-being, but also vital to the health and well-being of economic and environmental services. Tools such as the water footprint provide cities information about the volume of water required to sustain economic output and growth. A city's total water footprint contains two distinct components: its internal and external water footprint. Managing the internal water footprint has traditionally been the missions of municipal water managers, while a city's external footprint has been discounted because these impacts occur outside of the water management area. Despite being historically overlooked as academic information, the water outsourced by a city is used to produce necessary inputs to a city's economy, making this fraction of the total water footprint integral to the success of a city. To create actionable water footprint information for corporate and municipal sustainability decision making, water footprints must, by necessity, have two qualities formerly lacking: (1) an appropriately fine spatio-temporal scale of both the economic and hydrological sides of the watershed-economy connection, and (2) a robust representation of the relationship between water consumption and the scarcity of water, or the aquatic impacts at the point of use. By geographically disaggregating a city's external water footprint, city managers can begin to understand the water-related risks and vulnerabilities of its supply chain and create strategic partnerships to bolster the resilience of its outsourced water supplies. For this purpose, the Trade Dependence on Over-Allocated Water (TDOW) Database was created. The TDOW Database was used to geographically disaggregate a medium-sized city's (ca. 70,000 people) water footprint at the HUC-12 watershed level and subsequently the HUC-12 and intra-metropolitan scale for a large metropolitan city (>3,000,000 people). City-level water footprint vulnerability indices were then created for each metropolitan area in the United States using the TDOW Database. Methods:: Methods were developed for this study to calculate virtual water flows from municipal- and international-level bilateral trade data. The trade data encompasses flows of primary, secondary and tertiary goods from origin to destination. Trade data was obtained from United Stated Department of Transportation Freight Analysis Framework (FAF3) and international-level trade data was obtained from the World Bank World Integrated Trade Solution (WITS) database. Water consumption data were obtained from the municipalities studied, the United States Geological Survey, and the Water Footprint Network WaterStat database. Water stress was measured using the Water Stress Index developed by Sandia National Labs at the HUC-12 watershed level. A novel method for calculated a geographically-weighted Water Stress Index of Trade was created for this study and calculated for each metropolitan area in the United States. Results/Discussion: Through trade, a city may be exposed to external hydrological risks and vulnerabilities that have the potential to disrupt local economic processes. Risks that are present in a city's outsourced water supply are particularly exigent because the majority of water consumed by a city's economic processes are outsourced to non-local water sources, which each have their own set of hydrologic, ecologic, economic, and regulatory risks and vulnerabilities. For smaller cities, where trade is predominantly regional, local water stress may be exacerbated by the city's limited economic sphere of influence. Small cities were found more likely to have a water stress index of trade greater than local water stress. This was because trade was either almost predominantly local or the city fell under a larger city's sphere of influence that had higher levels of water stress. For these small cities, a more resilient economic trade network can be built by incorporating water stress metrics into purchasing decisions and diversifying from historic, regional trade patterns. However, in large cities trade takes places at the global scale. By tapping non-regional virtual water resources, large cities with global trade networks were found most likely to have a water stress index of trade less than its local water stress index. Additionally, geographically disaggregated water footprints were used to identify shared watersheds that could provide the basis for regional collaboration and shared planning. Conclusion: In recent years, the dominant foreign policy narrative has become, "foreign policy is domestic policy." The results of this study echo these sentiments: water-related risks and vulnerabilities within a city's economic trade network present a unique set of challenges that must be considered along with the management of local water resources. This work provides the first attempt at creating actionable and comprehensive watershed-level water footprint information for the United States. By geographically disaggregating a city's water footprint, decision-makers can incorporate water outsourcing strategies into municipal and corporate planning. However, there are limitations to the TDOW Database that require further work, such as refining the scale of analysis to include individual- and corporation-level footprints and incorporating a seasonal-timescale ecohydrological watershed model to quantify aquatic impacts in addition to long-term water stress. As cities undergo water stress from prolonged drought or changing climatic patterns, interdependencies in a city's virtual water trade network present opportunities for regional collaboration, which holds the potential to create a more resilient socio-hydrological system.

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