Focus on Resource Requirements of Future Urbanization

Distributed photovoltaics (PV) have played a critical role in the deployment of solar energy, currently making up roughly half of the global PV installed capacity. However, there remains significant unused economically beneficial potential. Estimates of the total technical potential for rooftop PV systems in the United States calculate a generation comparable to approximately 40% of the 2016 total national electric-sector sales. To best take advantage of the rooftop PV potential, effective analytic tools that support deployment strategies and aggressive local, state, and national policies to reduce the soft cost of solar energy are vital. A key step is the low-cost automation of data analysis and business case presentation for structure-integrated solar energy. In this paper, the scalability and resolution of various methods to assess the urban rooftop PV potential are compared, concluding with suggestions for future work in bridging methodologies to better assist policy makers.

Urban metabolism is a growing field of study into resource flows through cities, and how these could be managed more sustainably. There are two main schools of thought on urban metabolism—metabolic flow analysis (MFA) and urban political ecology (UPE). The two schools remain siloed despite common foundations. This paper reflects on recent research by the Gauteng City-Region Observatory (GCRO) into urban sustainability transitions in South Africa's Gauteng City-Region, a large and sprawling urban formation that faces a host of sustainability challenges including water deficits, erratic electricity supply, stretched infrastructure networks and increasingly carbon-intensive settlement patterns. Three GCRO research projects are reviewed. Each project began with the assumption that data collection on the region's metabolism could enable an MFA or MFA-like analysis to highlight where possible resource efficiency and sustainability gains might be achieved. However, in each case we confronted severe data-limitations, and ended up asking UPE-style questions on the reasons for and implications of the chronic paucity of urban metabolism data. We have been led to conclude that urban metabolism research will require much more than just assembling and modelling flows data, although these efforts should not be abandoned. A synthesis of MFA and UPE is needed, which simultaneously builds a deeper understanding of resource flows and the systems that govern these flows. We support the emerging approach in political-industrial ecology literature which values both material data on and socio-political insight into urban metabolism, and emphasises the importance of multi-disciplinary and multi-dimensional analysis to inform decision-making in urban sustainability transitions.

The transition to sustainable resource efficient cities calls for new governance arrangements. The awareness that the doubling of the global urban population will result in unsustainable levels of demand for natural resources requires changes in the existing socio-technical systems. Domestic material consumption could go up from 40 billion tons in 2010, to 89 billion tons by 2050. While there are a number of socio-technical alternatives that could result in significant improvements in the resource efficiency of urban systems in developed and developing countries (specifically bus-rapid transit, district energy systems and green buildings), we need to rethink the urban governance arrangements to get to this alternative pathway. We note modes of urban governance have changed over the past century as economic and urban development paradigms have shifted at the national and global levels. This time round we identify cities as leading actors in the transition to more sustainable modes of production and consumption as articulated in the Sustainable Development Goals. This has resulted in a surge of urban experimentation across all world regions, both North and South. Building on this empirically observable trend we suggest this can also be seen as a building block of a new urban governance paradigm. An 'entrepreneurial urban governance' is proposed that envisages an active and goal-setting role for the state, but in ways that allows broader coalitions of urban 'agents of change' to emerge. This entrepreneurial urban governance fosters and promotes experimentation rather than suppressing the myriad of such initiatives across the globe, and connects to global city networks for systemic learning between cities. Experimentation needs to result in a contextually appropriate balance between economic, social, technological and sustainable development.

Utilizing low-grade waste heat from industries to heat and cool homes and businesses through fourth generation district energy systems (DES) is a novel strategy to reduce energy use. This paper develops a generalizable methodology to estimate the energy saving potential for heating/cooling in 20 cities in two Chinese provinces, representing cold winter and hot summer regions respectively. We also conduct a life-cycle analysis of the new infrastructure required for energy exchange in DES. Results show that heating and cooling energy use reduction from this waste heat exchange strategy varies widely based on the mix of industrial, residential and commercial activities, and climate conditions in cities. Low-grade heat is found to be the dominant component of waste heat released by industries, which can be reused for both district heating and cooling in fourth generation DES, yielding energy use reductions from 12%–91% (average of 58%) for heating and 24%–100% (average of 73%) for cooling energy use in the different cities based on annual exchange potential. Incorporating seasonality and multiple energy exchange pathways resulted in energy savings reductions from 0%–87%. The life-cycle impact of added infrastructure was small (<3% for heating) and 1.9% ~ 6.5% (cooling) of the carbon emissions from fuel use in current heating or cooling systems, indicating net carbon savings. This generalizable approach to delineate waste heat potential can help determine suitable cities for the widespread application of industrial waste heat re-utilization.

As cities grow, their environmental and natural resource footprints also tend to grow to keep up with the increasing demand on essential urban services such as passenger transportation, commercial space, and thermal comfort. The urban infrastructure systems, or socio-technical systems providing these services are the major conduits through which natural resources are consumed and environmental impacts are generated.

This paper aims to gauge the potential reductions in environmental and resources footprints through urban transformation, including the deployment of resource-efficient socio-technical systems and strategic densification. Using hybrid life cycle assessment approach combined with scenarios, we analyzed the greenhouse gas (GHG) emissions, water use, metal consumption and land use of selected socio-technical systems in 84 cities from the present to 2050. The socio-technical systems analyzed are: (1) bus rapid transit with electric buses, (2) green commercial buildings, and (3) district energy. We developed a baseline model for each city considering gross domestic product, population density, and climate conditions. Then, we overlaid three scenarios on top of the baseline model: (1) decarbonization of electricity, (2) aggressive deployment of resource-efficient socio-technical systems, and (3) strategic urban densification scenarios to each city and quantified their potentials in reducing the environmental and resource impacts of cities by 2050.

The results show that, under the baseline scenario, the environmental and natural resource footprints of all 84 cities combined would increase 58%–116% by 2050. The resource-efficient scenario along with strategic densification, however, has the potential to curve down GHG emissions to 17% below the 2010 level in 2050. Such transformation can also limit the increase in all resource footprints to less than 23% relative to 2010. This analysis suggests that resource-efficient urban infrastructure and decarbonization of electricity coupled with strategic densification have a potential to mitigate resources and environmental footprints of growing cities.

This paper develops a methodology to assess the resource requirements of inclusive urban development in India and compares those requirements to current community-wide material and energy flows. Methods include: (a) identifying minimum service level benchmarks for the provision of infrastructure services including housing, electricity and clean cooking fuels; (b) assessing the percentage of homes that lack access to infrastructure or that consume infrastructure services below the identified benchmarks; (c) quantifying the material requirements to provide basic infrastructure services using India-specific design data; and (d) computing material and energy requirements for inclusive development and comparing it with current community-wide material and energy flows. Applying the method to ten Indian cities, we find that: 1%–6% of households do not have electricity, 14%–71% use electricity below the benchmark of 25 kWh capita-month⁻¹; 4%–16% lack structurally sound housing; 50%–75% live in floor area less than the benchmark of 8.75 m² floor area/capita; 10%–65% lack clean cooking fuel; and 6%–60% lack connection to a sewerage system. Across the ten cities examined, to provide basic electricity (25 kWh capita-month⁻¹) to all will require an addition of only 1%–10% in current community-wide electricity use. To provide basic clean LPG fuel (1.2 kg capita-month⁻¹) to all requires an increase of 5%–40% in current community-wide LPG use. Providing permanent shelter (implemented over a ten year period) to populations living in non-permanent housing in Delhi and Chandigarh would require a 6%–14% increase over current annual community-wide cement use. Conversely, to provide permanent housing to all people living in structurally unsound housing and those living in overcrowded housing (<5 m cap⁻²) would require 32%–115% of current community-wide cement flows. Except for the last scenario, these results suggest that social policies that seek to provide basic infrastructure provisioning for all residents would not dramatically increasing current community-wide resource flows.

Urban material resource requirements are significant at the global level and these are expected to expand with future urban population growth. However, there are no global scale studies on the future material consumption of urban areas. This paper provides estimates of global urban domestic material consumption (DMC) in 2050 using three approaches based on: current gross statistics; a regression model; and a transition theoretic logistic model. All methods use UN urban population projections and assume a simple 'business-as-usual' scenario wherein historical aggregate trends in income and material flow continue into the future. A collation of data for 152 cities provided a year 2000 world average DMC/capita estimate, 12 tons/person/year (±22%), which we combined with UN population projections to produce a first-order estimation of urban DMC at 2050 of ~73 billion tons/year (±22%). Urban DMC/capita was found to be significantly correlated (R² > 0.9) to urban GDP/capita and area per person through a power law relation used to obtain a second estimate of 106 billion tons (±33%) in 2050. The inelastic exponent of the power law indicates a global tendency for relative decoupling of direct urban material consumption with increasing income. These estimates are global and influenced by the current proportion of developed-world cities in the global population of cities (and in our sample data). A third method employed a logistic model of transitions in urban DMC/capita with regional resolution. This method estimated global urban DMC to rise from approximately 40 billion tons/year in 2010 to ~90 billion tons/year in 2050 (modelled range: 66–111 billion tons/year). DMC/capita across different regions was estimated to converge from a range of 5–27 tons/person/year in the year 2000 to around 8–17 tons/person/year in 2050. The urban population does not increase proportionally during this period and thus the global average DMC/capita increases from ~12 to ~14 tons/person/year, challenging resource decoupling targets.