Cities as Sustainable Ecosystems:
A Systems Framework for Sustainable Urban Development

	Hari Srinivas
	Concept Note Series E-143.

Abstract: A city must have adequate infrastructure and flexibility to support the needs of its population. As in the case of the global system as a whole, cities must not use resources faster than they can be replenished or substituted for, nor generate pollution faster than it can be assimilated. One of the guiding principles for the future will be to reform urban systems so that they mimic the metabolism of nature. Rather than devouring water, food, energy, and processed goods, and then belching out the remains as pollutants, the city could align its consumption with realistic needs, produce more of its own food and energy, and put much more of its waste to use. Looking at cities as sustainable ecosystems draws its inspiration from the cyclical ecosystems of nature itself. It is sensitive to global impacts of local consumption and production patterns, and takes an interdisciplinary and interlinked approach in developing its activities, outputs and partners. Developing cities as sustainable ecosystems requires a radical increase in the productivity of the resources it uses, and the goods and services it produces. This entails changes in both production, design and technology stretch the utility value of energy, minerals, water, and other natural resources. Closed-loop systems return every output harmlessly back to the ecosystem, or become an input to another process. This requires consumption and production systems that are modeled after the cyclical ecosystems of nature itself.

Keywords: Urban environmental management, Sustainable ecosystems, Urbanization, Ecological footprint, Urban metabolism, Sustainable development, Built environment, Environmental policy

Environment as the Common Denominator

"Today's concepts such as circular economy, urban metabolism, regenerative cities, and nature-based solutions all build upon the ecosystem perspective described in this paper." See ANNEX below for an exploration of these emerging concepts

The concern and problems associated with the environment have placed such issues high on the agenda of many bilateral and multilateral meetings. The Earth Summit of 1992 in Rio de Janeiro managed to highlight and channel efforts in understanding and acting on environmental problems, making it a key issue to be tackled in trade and commerce, in economic and social development, and in science and technology. Subsequent summits and congresses the Social Summit and the Beijing Conference on Women in 1995, the City Summit/Habitat II in 1996, not to mention innumerable regional, national and local meetings all had the larger global environment as a key common denominator in its action plans.

More recently, the Post-2015 Agendas, including the SDGs, have further enhanced the criticality of environmental issues and the need for their integration in public policy making. When the Millennium Development Goals (MDGs) ended in 2015, the international community came together once again, under the auspices of the United Nations, to formulate a set development agenda for adoption beyond 2015. These agendas (which go beyond the SDGs themselves) collectively became known as the "Post-2015 Agendas". They include the SDGs, the UN Climate Change convention, Finance for Development Agenda, Sendai Framework on Disaster Risk Reduction, the Humanitarian Agenda, and the Habitat Agenda.

It is only in the last few decades that a better understanding of the effects of changing environments and ecosystems has been developed. Interconnectedness of these factors has forced particular attention on human lifestyles and living conditions that has a profound effect on its surroundings. Most, if not all, environmental problems that we currently face can be directly or indirectly traced back to the legacy of lifestyles that we are inheriting and leading as human beings. Nowhere is this more true that in concentrations of gregarious urban lifestyles that are becoming the option of choice for the majority of humanity.

The Master Culprit: Urban Environments

By the turn of this century, we were witness to a ubiquitous scenario where more people opted to live in and around cities than in rural areas. In the following decades, this urban shift has only accelerated. Today, over 55% of the global population resides in urban areas - a figure projected by the United Nations to reach nearly 70% by 2050. This rapid transformation cements cities not just as demographic hubs, but as the primary arenas where the future of global environmental sustainability will be decided.

The world's cities take up just two percent of the Earth's surface, yet account for roughly 78 percent of the carbon emissions from human activities, 76 percent of industrial wood use, and 60 percent of the water tapped for use by people.

In 1800, only 50 million people lived in towns and cities worldwide. During 1975, there were 1.5 billion, and by the year 2000, this became three billion - more than the entire population of the world in 1960. Proximity to decision-makers and financial markets, large pools of skilled and unskilled workers, and other advantages have made such urban areas the engines of growth for the countries and regions where they are situated. For example, despite the environmental and social problems that it is facing, Bangkok's contribution to the national GDP has been estimated to be more than the combined output of all other cities in Thailand.

The result of this has been the explosive growth of urban areas, bringing with it a host of negative effects. Population concentration in increasingly smaller land masses has caused a drastic decline in the quality of living both in the residential and work fronts. Cities have, in effect, become a barometer of humankind's progress into the 21st century, whether this is an upward or downward trend. Such a scenario has had ripple effects on a variety of sectors such as education, health, labour/job markets, and economic activities.

The growth and effect of an urban area should be seen not only in terms of its immediate boundaries, but also in terms of the resources necessary to sustain its population. An illustrative example is that of the Greater London area. The land mass that generates the resources necessary to sustain the population of London, called the 'urban footprint,' is actually slightly less than the entire land area of UK! This illustrates the complex interrelationship and interdependence of urban areas and their surrounding hinterland.

For example, based on GDRC research, Japanese lifestyles generate a demand for approximately 6.25 global hectares (gha) of biologically productive land and sea per person to provide resources and absorb wastes. However, Japan's own ecosystems provide only about 1.88 gha per person, leaving an ecological deficit of 4.37 gha per person that must be met through imports or by drawing on global ecological resources.

The Greater Tokyo metropolitan region had an estimated population of 37.4 million in 2025. For Tokyo alone, this ecological deficit amounts to approximately 163.4 million global hectares, equivalent to about 4.3 times the total land area of Japan. If only Japan's habitable land is considered, excluding mountains, forests unsuitable for settlement, and inland water bodies, the deficit corresponds to roughly 13.4 times the country's habitable land area.

The effects of urban activities have in many cases outweighed the relative advantages of agglomeration and centrality that they have offered. Thus, along with the benefits of urbanization come environmental and social ills, including lack of access to drinking water and sanitation services, pollution and carbon emissions etc. A wide variety of urban problems can be observed, grouped under two broad contradictive classes, those associated with poverty and those associated with economic growth and affluence.

Environmental Management of Cities

Burgeoning cities are expanding into fragile ecosystems ... Cities sometimes deplete nearby areas of water and firewood, rendering them less capable of supporting rural populations and thus adding to the pressures for urban migration. Air pollution already exceeds health standards in many megacities in developing countries. Sewage and industrial effluents are released into water-ways with minimal or no treatment, threatening human health and aquatic life. Some urban environmental problems such as access to safe drinking water improve with economic growth, while others tend to worsen.

Thus in the absence of policy reform, stronger institutions, and enlightened political leadership, economic and population growth in developing countries in the near term may lead to a deterioration of the urban environment, both physical and social. Stresses on the global environment from urban activities are also likely to accelerate. A major share of greenhouse gas emissions already comes from the use of fossil fuels in wealthy urban areas, especially in the developed countries.

While laws exist to effect interaction and participation between the various actors involved in urban growth processes, it is not adequately exercised both on the part of local governments (sufficient information was not provided), as well as other actors and citizens themselves (there was no commitment to participate). Information that is shared by the government is, in many cases, partial or selective. There has, however, been a growing awareness of environmental problems and its causes and effects.

With a gradual increase in the transparency and openness in the functional organization and operation of local governments, legislation on information disclosure has been receiving considerable importance. Basic understanding of environmental management of cities and the consequent needs of information for decision making processes has also improved. Community involvement becomes all the more critical when the shortcomings and weaknesses of local governments to effectively deal with the range of problems are taken into account. All this has necessitated a hard rethinking and reexamination of the intrinsic and symbiotic (negative and positive) relationships between human lifestyles and natural resources that is depended upon.

Figure 2: The Three Dimensons of Urban Environments

It is helpful therefore, to look at urban environments from three view points: the natural environment, the built environment and the socio-economic environment. Natural environments are essentially resources, processes and effects related to flora and fauna, human beings, minerals, water, land, air, etc. Built environments are resources, processes and effects related to buildings, housing, roads, railways, electricity, water supply, gas etc. The socio-economic environment includes resources, processes and effects related to human activities, education, health, arts and culture, economic and business activities, heritage - urban lifestyles in general. It is the intersection and overlay of these three dimensions that constitutes an 'urban environment'.

Taking any one dimension at the exclusion of the other two, poses the inevitable danger of missing the forest for the trees - the interdependency and interdisciplinarity of the three dimensions have to be fully understood in the development of coherent and sustainable policies and programmes for the urban environment. This is particularly true with the multiplicity of actors and activities - there has been a growing realization that state agencies and activities are, but one part of a spectrum of agencies and activities that are involved in the urban environment.

Interaction between the different actors at different levels of urban growth processes and cycles becomes critical to respond to the increasingly complex policy and investment choices that urban communities face. There are many key points that arise in support of a sound urban environmental policy. The concept of sustainable development ought to take into account the needs of future generations in decisions on how and whether to use resources and apply technologies, through policies, investments and development plans.

Looking at Cities as Ecosystems

One of the guiding principles for the future will be to reform urban systems so that they mimic the metabolism of nature.

The metabolic shift, of mimicing nature as a model, is operationalized through the principles of the Circular Economy. Rather than adhering to a linear "take-make-waste" industrial model, a circular urban ecosystem prioritizes decoupling economic activity from the consumption of finite resources. By embedding a Materials, Energy, Water, and Waste (MEWW) framework into local planning, cities can systematically audit their resource flows, ensuring that every output either safely returns to the biosphere or becomes a high-value input for another urban process.

To systematically track and manage this urban metabolism, planners can utilize the MEWW (Materials, Energy, Water, and Waste) framework. This diagnostic approach treats a city as a living organism by auditing its four critical resource flows:

• Materials: Optimizing the life cycle of physical assets, timber, and minerals to promote urban reuse and reduce raw extraction.
• Energy: Transitioning to localized renewable grids and improving structural efficiency to decouple urban growth from carbon emissions.
• Water: Implementing closed-loop conservation, rainwater harvesting, and localized wastewater treatment to protect regional watersheds.
• Waste: Shifting from disposal to recovery, transforming outputs into valuable inputs for other urban and agricultural systems.

By balancing these four interconnected pillars, the MEWW framework provides municipalities with a concrete, measurable roadmap to convert linear urban supply chains into circular, self-sustaining loops.

Environmental policies have to be based on an understanding of the causes of environmental degradation and of the environmental impacts and cost-effectiveness of solutions, as well as the uncertainties associated with it. Policies should also contribute to greater public understanding of environmental issues through more open access to information and decision-making process. Operationalizing environmental policies, therefore, require the integration of many interrelated economic, environmental, social and cultural factors.

Consolidating the ideas and issues together is the ecosystem approach. An urban ecosystem brings together the resources, processes and products into a coherent system that exchanges and makes use of byproducts and/or energy - aiming towards the reduction in the use of virgin materials as resource inputs; reduction in pollution; increased energy efficiency leading to reduced energy use in the system as a whole; reduction in the volume of waste products requiring disposal (with the added benefit of preventing disposal-related pollution); and increase in the amount and types of process outputs that have market value.

A city must have adequate infrastructure and flexibility to support the needs of its population, and the needs of the ecosystem as a whole. As in the case of the global system as a whole, cities must not use resources faster than they can be replenished or substituted for, nor generate pollution faster than it can be assimilated. One of the guiding principles for the future will be to reform urban systems so that they mimic the metabolism of nature. Rather than devouring water, food, energy, and processed goods, and then belching out the remains as pollutants, the city could align its consumption with realistic needs, produce more of its own food and energy, and put much more of its waste to use.

Looking at cities as sustainable ecosystems draws its inspiration from the cyclical ecosystems of nature itself. It is sensitive to global impacts of local consumption and production patterns, and takes an interdisciplinary and interlinked approach in developing its activities, outputs and partners.

Millennium Ecosystem Assessment The Millennium Ecosystem Assessment (MA) - a multistakeholder international effort - is a four-year process designed to improve the management of the world's natural and managed ecosystems by helping to meet the needs of decision-makers and the public for peer-reviewed, policy-relevant scientific information on the condition of ecosystems, consequences of ecosystem change, and options for response. The MA will provide information and also build human and institutional capacity to provide information. More specifically, the MA will, among other outputs, significantly increase understanding of the linkage between ecosystems and the goods and services they provide, build human capacity and capacity of global, regional, national and local institutions to undertake integrated ecosystem assessments and act on their findings, strengthen international environmental agreements and improve environment-related decisions of national governments by improving access to the best scientific information and support regional, national, and local integrated assessments that will directly contribute to planning and capacity-building needs. The MA will provide the scientific underpinning to a wide range of national and international efforts to address environment and development challenges. These environmental challenges are interwoven, and thus an integrative assessment process is needed to highlight for decisionmakers the linkages among climate, biodiversity, freshwater, marine and forest issues. Since the Millennium Ecosystem Assessment, ecosystem thinking has been further advanced through the Sustainable Development Goals, the New Urban Agenda, nature-based solutions, circular economy and other approaches, all of which originate from, and reinforce, the ecosystem perspective. [See Annex 2 below, for a list of these approaches] Source: http://www.ma-secretariat.org/

Developing cities as sustainable ecosystems requires a radical increase in the productivity of the resources it uses, and the goods and services it produces. This entails changes in both production, design and technology stretch the utility value of energy, minerals, water, and other natural resources. Closed-loop systems return every output harmlessly back to the ecosystem, or become an input to another process. This requires consumption and production systems that are modeled after the cyclical ecosystems of nature itself.

This clearly needs an objective, multidisciplinary study of urban and economic systems and their linkages with fundamental natural systems. Research on energy supply and use, new materials, new technologies and technological systems, and other relevant issues is critical for a better understanding of the issues involved.

In a broader sense, the ecosystem approach should be applied at all levels of resource consumption in a city - from building design and construction and its use, to macro scale issues of urban planning and development, urban management, network and social infrastructure (roads, electricity, gas, telecommunications, schools, hospitals etc.).

The urban ecosystem approach raises several critical needs:

Ecological footprints of cities needs to be identified Understanding the dependence of urban residents on not only its immediate hinterland, but also on far away places and resources for its everyday life - i.e. its ecological footprint, will assist in developing the concept of urban ecosystems - where resources are used, and wastes and pollution generated. How will the footprint analyses lead to better understanding of urban ecosystems? What intangible awareness-raising role can it play to induce action among urban residents? How can better material flows be developed from footprint analyses? Global trends to develop local environment activities There is a clear need to link global environmental problems to action at the local level. Most global problems are in fact a result of smaller, more local actions (for example, increased use of cars at the local level leading to global warming). Thus, urban ecosystems need to be understood keeping global issues and trends in mind. How can this global-to-local environment continuum be built? What cause-effect cycles can be identified? What implications do multilateral environmental agreements have in inspiring local action? Partnerships need to be developed among all local actors Quite clearly, partnerships for managing the urban ecosystem are complex - it is not the local government alone that can solve the problems at the local level. All local actors - businesses, NGO/NPOs, citizens groups, schools and universities and others - need to be involved in partnership so that the strengths and capacities of one actor can overcome the shortcoming or deficiencies of another actor, thus leading to better concerted action. What partnership dynamics are at play in an urban ecosystem? What resources, skills, and knowledge do these actors bring to the table? What are the success factors that will build such effective partnerships? In-depth and intensive scientific research is needed There is a critical need for in-depth and intensive scientific/technological research on the ecosystem approach in order to understand the causes and effects of our everyday lifestyles, and guide policy development for a sustainable city. What are the critical issues that need to be researched and studied within an urban ecosystem? What lessons can we adopt from natural ecosystems and cycles to an urban setting? How can a core behaviour change among urban residents be effected using the ecosystem approach? Existing environmental management functions and actions need to be integrated Urban design, planning, implementation and management - particularly of infrastructure - is fragmented and uncoordinated. Quite clearly, the overarching nature of the ecosystem approach needs to be taken advantage of in enabling an integrative approach to managing the environment of a city. Where are these points of integration and overlap? What micro (at the building and community levels) and macro (at the broader city level) issues need to be taken into account in operationalizing the urban ecosystem approach?

Emerging Needs (2025 and beyond) The ecosystems approach will have to to be contextualized within a number of other emerging topics as well: Digital Twins Cities are increasingly using digital replicas of urban systems to simulate development scenarios, optimize infrastructure, and improve planning and emergency response. AI-assisted Urban Management Artificial intelligence is enabling more informed and timely decision making by analyzing large volumes of urban data to improve transport, energy use, public services, and environmental monitoring. Circular Resource Systems Future cities must move beyond the traditional "take-make-dispose" model by designing systems that minimize waste, recover valuable resources, and keep materials in continuous use. Climate Adaptation As the impacts of climate change intensify, cities need to strengthen their resilience through adaptive infrastructure, risk-informed planning, and nature-based solutions that protect communities and ecosystems. Urban Biodiversity Protecting and restoring biodiversity within cities contributes to healthier ecosystems, enhances residents' well-being, and improves resilience to environmental change. Social Resilience Sustainable cities depend on strong, inclusive communities that are able to anticipate, withstand, and recover from economic, environmental, and social disruptions. Data Governance The growing availability of urban data requires transparent governance frameworks that ensure data quality, privacy, security, equitable access, and responsible use in decision making. Citizen Science Engaging residents in collecting, sharing, and interpreting environmental data strengthens public participation, improves local knowledge, and fosters collaborative urban governance.

Ultimately, there is a need to create an impetus for change and to guide and direct that change to achieve real, demonstrable results. This will clearly require action to create/build a commitment to the pursuit of the sustainability concept, and then move towards creating a creating an organization with a shared commitment to the pursuit of shared goals. These two fundamental steps are necessary to generate broad support, external and internal, to the pursuit of sustainable objectives .

ANNEX 1 Case Studies Urban sustainability is best understood through practice. The following examples illustrate how cities around the world have applied ecosystem thinking to address challenges related to water, resources, mobility, and resilience. Although each city reflects its own geographical, economic, and cultural context, together they demonstrate that sustainable urban development depends on understanding and managing the complex interactions between natural, built, and socio-economic systems.  Singapore: Water Security and Closing the Urban Water Loop Singapore has transformed its limited freshwater resources into a resilient urban water system through an integrated approach that combines rainwater harvesting, desalination, imported water, and the recycling of treated wastewater (NEWater). By viewing water as a renewable urban resource rather than a waste product, Singapore demonstrates how ecosystem thinking can enhance water security, resource efficiency, and climate resilience.  Kitakyushu, Japan: From Industrial Pollution to Circular Economy Once known for severe industrial pollution, Kitakyushu has become an international model of sustainable urban transformation. Through strong partnerships between government, industry, and local communities, the city has reduced pollution, promoted resource recovery, and developed eco-industrial networks in which the waste from one enterprise becomes a resource for another. Its experience illustrates the practical application of circular economy principles within an urban ecosystem.  Curitiba, Brazil: Integrating Land Use and Sustainable Mobility Curitiba is internationally recognized for pioneering the Bus Rapid Transit (BRT) system and integrating transport planning with land use and environmental management. By encouraging compact urban development along major transport corridors, the city has reduced congestion, improved accessibility, and enhanced environmental quality. The Curitiba experience demonstrates how coordinated urban systems can improve both efficiency and quality of life.  Kobe, Japan: Building Urban Resilience Through Recovery and Preparedness Following the Great Hanshin-Awaji Earthquake of 1995, Kobe rebuilt its infrastructure while strengthening community preparedness, disaster risk reduction, and resilient urban planning. Investments in safer buildings, emergency response systems, public education, and community participation have helped create a city that is better prepared for future hazards. Kobe illustrates how resilience is strengthened not only through physical infrastructure but also through social capital, effective governance, and continuous learning. Snapshots of Other Cities Applying the Ecosystem Approach Amsterdam, Netherlands - [Circular Economy] Advancing a circular economy through resource recovery, material reuse, and circular construction. Bogota, Colombia - [Mobility] Integrating public transport, green corridors, and public spaces to improve environmental quality and social inclusion. Copenhagen, Denmark - [Mobility] [Climate] Pursuing carbon neutrality through cycling, renewable energy, district heating, and climate adaptation. Freiburg, Germany - [Urban Form] Combining compact urban development, renewable energy, green buildings, and citizen participation. Melbourne, Australia - [Climate] [Nature-based Solutions] Expanding urban forests and water-sensitive urban design to address heat islands and climate resilience. Portland, USA - [Urban Form] Protecting urban growth boundaries while promoting sustainable transport, green infrastructure, and compact development. Rotterdam, Netherlands - [Water] [Resilience] Using innovative water management, floating infrastructure, and climate adaptation to live with rising sea levels. Seoul, Republic of Korea - [Nature-based Solutions] Restoring the Cheonggyecheon Stream to improve biodiversity, reduce urban heat, and revitalize the city centre. Shanghai, China - [Water] Implementing sponge city principles through permeable surfaces, wetlands, and green infrastructure to improve stormwater management. Stockholm, Sweden - [Integrated Sustainability] Developing eco-districts that integrate energy efficiency, waste management, sustainable transport, and green spaces. Vancouver, Canada - [Climate] Advancing green buildings, active transportation, urban biodiversity, and renewable energy under its Greenest City strategy. Yokohama, Japan - [Integrated Sustainability] Reducing greenhouse gas emissions through integrated waste management, energy efficiency, and community participation.

ANNEX 2 Contemporary Concepts in Sustainable Urban Development A number of recent concepts in sustainable urban development have their precedences in the ecosystems approach, listed below. Collectively, these concepts represent the evolution of ecosystem thinking in urban development. While each emphasizes a different dimension of sustainability, all share the recognition that cities function as interconnected socio-ecological systems whose long-term prosperity depends on balancing environmental integrity, economic vitality, and social well-being. In this sense, they extend and reinforce the ecosystem perspective presented in this paper. Circular Economy ➤ The circular economy is an economic model that seeks to eliminate waste by keeping materials, products, and resources in continuous use through reuse, repair, remanufacturing, and recycling. In cities, it promotes resource efficiency, reduces environmental impacts, and creates new economic opportunities while supporting sustainable consumption and production. Urban Metabolism ➤ Urban metabolism views a city as a living system through which resources such as energy, water, food, and materials flow, are transformed, and eventually leave as products, services, waste, and emissions. Understanding these flows helps identify opportunities to improve resource efficiency, reduce pollution, and enhance urban sustainability. Nature-based Solutions ➤ Nature-based solutions use natural ecosystems and ecological processes to address urban challenges such as flooding, heat stress, air pollution, and biodiversity loss. Examples include urban forests, wetlands, green roofs, and restored rivers, which provide environmental, social, and economic benefits simultaneously. One Health ➤ One Health recognizes that the health of people, animals, and ecosystems is closely interconnected. In urban areas, this approach encourages integrated policies that address public health, environmental quality, biodiversity conservation, and disease prevention as part of a single sustainable development strategy. Sponge Cities ➤ A sponge city is designed to absorb, store, filter, and gradually release rainwater through green infrastructure such as parks, wetlands, permeable pavements, and green roofs. By working with natural hydrological processes, sponge cities reduce flooding, improve water quality, replenish groundwater, and enhance urban resilience. 15-minute Cities ➤ The 15-minute city is an urban planning concept in which residents can reach most daily needs, including work, education, healthcare, shopping, and recreation, within a 15-minute walk or bicycle ride from their homes. The approach promotes accessibility, reduces dependence on private vehicles, strengthens local communities, and improves quality of life. Regenerative Cities ➤ Regenerative cities aim not only to reduce environmental impacts but also to restore and enhance natural ecosystems, social well-being, and local economies. Rather than simply sustaining existing conditions, they seek to create urban systems that actively improve environmental quality and generate positive benefits for future generations. Climate Resilience ➤ Climate resilience refers to a city's ability to anticipate, prepare for, respond to, and recover from the impacts of climate change, including extreme weather events, rising temperatures, flooding, and sea-level rise. It combines infrastructure improvements, ecosystem restoration, effective governance, and community preparedness to reduce vulnerability and support long-term sustainability.

This work by GDRC is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. You are free to share and adapt this piece of work for your own purposes, as long as it is appropriately cited. More info: http://creativecommons.org/licenses/by-sa/4.0/ CITATION TEXT: 📋 Copy citation to clipboard

Return to the UEM Programme Contact: Hari Srinivas - [email protected]