General approaches for assessing urban environmental sustainability

doi:10.1016/j.cosust.2012.09.003

Current Opinion in Environmental Sustainability

Volume 4, Issue 4, October 2012, Pages 458-464

https://doi.org/10.1016/j.cosust.2012.09.003 Get rights and content

Urban environmental sustainability assessment is increasingly a part of urban planning, from the perspective of mitigating local and global impacts and for adapting to regional and global resource constraints and anticipated climate events.

We examine general techniques under three categories: consumption-based, metabolism-based and complex systems approaches. We sample recent and salient applications at spatial scales ranging from neighbourhoods to metropolitan regions.

The scope and strengths of applications in these categories are complementary especially with regards to the attribution of impact. The first approach assesses environmental sustainability as a function of urban consumption, the second uses a more limited concept of consumption but better represents local and trans-boundary production activity and the third attributes cause and effect through quantifying relationships and feedbacks throughout the urban system.

Highlights

► We examine useful methods for urban planning under three categories: consumption-based, metabolism-based and complex systems approaches. ► Applications for each category at relevant urban scales are discussed. ► The scope and strengths of applications are complementary, the use of hybrid or multiple approaches is recommended.

Introduction

Environmental sustainability has become an essential part of urban⁴ performance reporting and planning. Population pressure and proximity to resource limitations, current or anticipated exogenous environmental impacts and a greater sense of global responsibility have catalysed those planning or governing cities to be guided by studies of environmental sustainability.

This review is about recent developments in general approaches for environmental sustainability assessment specifically for cities. The criterion of ‘generality’ in our selection of methods includes applicability across scales and portability to different locations. We acknowledge the utility of other concepts and approaches that do not necessarily pass this test, for example, of urban ecology or regional science with emphases on history and geography. Often these approaches have case-specific or location-specific analysis that is not scalable or portable. We must also acknowledge that our scope excludes important location-specific indicators, for example, regarding biodiversity.

We review a selection of studies concerned with direct or indirect material and energy flows and place them into three categories based on their differences in concept and purpose (Figure 1). Consumption-based accounting (CBA) captures economy-wide impacts of urban consumption and lifestyles. Metabolism-based accounting (MBA) addresses direct consumption and production impacts within geopolitical boundaries though we include methodological extensions that record impacts from important cross-boundary supply chains. A third and more recently developed category we propose is ‘complex systems approaches’ which includes attempts at modelling the underlying dynamics of cities at various scales.

Our purpose is to survey these reporting and simulation tools and to present current examples of their actual or potential application for urban planning under reasonable conceptual headings. Our classification concurs with other recent views and reviews in the literature [1, 2•, 3, 4•, 5, 6••, 7•, 8, 9, 10•].

Environmental sustainability assessment may have two general purposes: monitoring and measuring the past or current environmental pressures, states, or impacts of urban areas, or simulating possible future scenarios of change. The monitoring and measurement functions of CBA and MBA are essentially retrospective in that they report what has happened. As ex-post methods they can indicate whether past policies have been successful or are on target to achieve the desired outcome. Their representation of the urban system is usually less complex than for simulation methods as only certain output indicators (e.g. emissions or water use) are recorded without the need to describe (dynamic) cause-effect relationships. The main purpose of simulation tools is exactly to represent dynamic, cause-effect relationships for generating and evaluating possible future scenarios. The deeper epistemic uncertainty inherent in simulation is a limitation but the aim is not precise prediction so much as understanding the urban system and the action of endogenous impacts, for example, increased population or economic activity and exogenous impacts, such as climate change [10•, 11, 12, 13, 14].

Environmental sustainability assessments should produce outputs about processes and performance at relevant urban scales for management interventions, recognising the limitations of management at those scales and appropriate levels of precision in reporting. We comment on the abovementioned techniques as they apply at various scales.

Section snippets

Consumption-based approach

CBA at the city scale establishes a link between the consumption levels and patterns of urban residents and the associated embodied environmental impacts, whether those impacts occur inside or outside the city boundary. The most commonly used method for CBA is environmentally extended input–output analysis (IOA) capable of assessing direct and indirect water [15••, 16, 17, 18, 19, 20, 21], and energy use [22•, 23, 24], ecological footprinting [16, 17, 25, 26, 27] and most notably greenhouse gas

Metabolism-based approach

MBA studies that record the material, water, waste and energy flows of an urbanized area have previously been defined by geo-political boundaries (the ‘territory’ of the area) but are increasingly being extended to include trans-boundary flows. We collect all these approaches within ‘metabolism-based accounting’, because of their roots in urban metabolism studies [50]. These have been concerned with aggregate environmental performance measures for cities at a macro-scale [51, 52, 53, 54, 55, 56

Complex systems approach

Reporting about urban performance and sustainability that concentrates on current or past aggregate data does not necessarily convey a better appreciation of urban dynamics, offer intervention points, or help address dynamic problems.

Complex systems approaches are not an amalgam of CBA and MBA, they recognize features such as system interactions [83], feedbacks [84], network relationships [85] and agency [86] and are intended for simulation and understanding of the dynamics more than for

Conclusions

We have presented examples of material and energy flow assessment approaches useful for environmental sustainability planning at the city scale. These have been arranged into three categories.

CBA has the most comprehensive system boundary but input–output databases rarely exist at the urban level and some additional scaling information is required to resolve environmental sustainability measures at urban or suburban scales. This adds some degree of uncertainty, for example, sampling errors in

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

• of special interest
•• of outstanding interest

Acknowledgement

The writing of this paper was funded by the Integrated Carbon Pathways project of the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia.

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