Feeding the Urban Metabolism within Planetary Boundaries - A Policy for future-proof Phosphorus Supply of a medium-sized Western European City with respect to its Global Hinterland
Cities as concentrated hubs of human activity generate 80% of global GDP, consume 70-75% of natural resources and eject 70% of the planet's waste (UNEP, 2017; UN Habitat, 2017). To satiate their demand, cities are intrinsically dependant on food supply from hinterlands rendering them responsible for global mobility of phosphorus. The element phosphorus is crucial to all life on Earth and is transported in the food supply chain which degrades agricultural soils requiring artificial fertilization. While mining deposits are depleting, health and food security of more than 54% of the global population are at stake (United Nations, 2014). Due to a lack of adequate international governance mechanisms in place, self-governing cities are left with the daunting task of reshaping the anthropogenic phosphorus consumption into a cycle to secure their survival. To test the method of urban phosphorus policy design through the lens of urban metabolism, this thesis answers the question: “How well can the medium-sized Western European city The Hague (NL) safeguard its food supply through a regional phosphorus policy that respects the phosphorus needs of the feeding hinterlands?” Based on review of relevant literature, a methodology of two stages of P policy design was generated and applied to the case study city: Firstly, an analysis of hinterland relations, biogeophysical, socioeconomic and governance dimensions of the regional context provided the foundation for a causal model of governance factors. Secondly, derived policy agenda goals are translated into supporting concrete measures that can be implemented utilizing instruments of various modes of governance. The considered data has been generated in a mixed method approach of qualitative expert interviews, literature review and quantitative substance flow modelling using the software STAN. The resulting impact on the modelled substance flows shows that the proposed policy reduces polluting emissions by 82%, mineral fertilizer imports by 49% and food-borne phosphorus imports by 10%. It increases phosphorus exports by 64% and offers an annual recovery potential from regional wastewater and solid waste flows of nearly one million euros. In conclusion, regional public governance authorities possess the means to substantially alleviate pressure on global hinterlands and ensure regional compliance with the Planetary Boundaries for phosphorus emissions. This thesis represents a first step into research of cumulative urban material governance and indicates the unused potential for increasing resilience of the urban metabolism in synergy with global feeding networks.