Is 'carrying capacity' a relevant tool to ensure sustainable growth in cities?
In the recent months, a National Green Tribunal NGT ) directive, ordering states to assess environmental loads for ecologically sensitive areas, has reignited discussions on  carrying capacity   broadly, the total number of individuals of a species that can live in an ecosystem under certain conditions. It acts as a parameter for determining thresholds of urban population in cities.Considering India s rapid urbanisation and the demand for resources which are fast depleting, understanding carrying capacity is a necessary starting point. But is it a sufficient condition for determining the limits of 21st century cities, which have multi-dimensional challenges and complex ecosystems?The concept of carrying capacity originated in the 1800s, and found its initial use in ecology and theories of planetary boundaries. Over decades, the term urban carrying capacity (UCC) evolved. This provided a theoretical foundation for determining the maximum potential population that could be supported without environmental degradation, based on the inherent limit of a given urban area. More recent literature on UCC has expanded the concept beyond ecology by including economic, social and infrastructure imperatives.Current methods for assessing carrying capacity mainly involve scoring across sectoral verticals against a set of parameters, chosen based on the question the study seeks to answer. Such scoring is useful on two accounts: one, applying the approach of planetary boundaries at a regional scale to determine limits of growth based on availability of resources; and two, assessing carrying capacity of an area against a specific parameter such as green spaces, and availability of schools and healthcare, as has been the practice in many city plans.For urban planning, however, with all its complexities and nuances like quality of life goals and contextual choices, the application of carrying capacity remains mired in controversy and contradictions. For instance, conventional sources of energy (such as fossil fuels) are a finite resource. Hence, it qualifies as a boundary condition in resource-centric carrying capacity assessment. At the same time, use of fossil fuel increases air pollution, thereby requiring a limit on the emissions that can be allowed within a particular jurisdiction, irrespective of its availability as a resource.Arguably, the latter can be used to determine the total vehicle carrying capacity in a city and that is what the NGT ordered in 2018 with respect to air pollution. However, vehicle carrying capacity from a pollution perspective is not static as it depends on factors such as access to clean technology, which may prove to be a game changer over time. Moreover, any limits to be put on a service or amenity would also need to consider factors such as affordability, access to alternate options and so on.Breaking down the components of carrying capacity based on their possibility of change over time and scale can offer useful insights. Natural reserves such as water, land, large forests, generally remain unchanged over long time periods from a planetary resource perspective and thus can be considered as static boundary conditions in assessing carrying capacity. However, given the nature of these elements, they may not be confined within a citys administrative boundaries, and thus, can be accounted for at a regional scale.On the other hand, there are components, such as infrastructure, that can be confined to a local/city scale and being dynamic in nature can have variable carrying capacities. For example, an area could accommodate higher urban population without increasing pressure on the citys energy resources by adopting progressive regulations for decentralized solutions such as solar rooftops, potentially increasing the carrying capacity of the city.Furthermore, the role of disruptive technologies cannot be overlooked in assessing UCC in todays world. Consider cab aggregator platforms which have transformed how people move in cities and access jobs and amenities, thus altering the transport sector carrying capacity. Thus, policy-making for cities is a balancing act that may be informed by relatively static boundary conditions at a regional scale and single-parameter carrying capacities at a city scale thats considered dynamic.Frameworks for assessing UCCs usually fall short as they largely remain focused on physical aspects. In order to grow sustainably, cities need to take into account institutional dimensions to bring coherence and acknowledge human behaviour, culture and perceptions. Informed decisions can only be made through inclusive stakeholder engagements and community participation processes.To incorporate this, effective planning and management of cities requires scales of planning  from regional to local along with vertical and horizontal coordination between plans. While a regional level plan offers a workable scale for setting boundary conditions for static components, the city/sub-regional level plans need to be cognisant of these boundary conditions while being informed by locally intrinsic parameters.Plans of different cities, within the same region, cannot be oblivious of each other as they are collectively responsible for staying within the boundary conditions set by the regional plan. The same goes for sectoral plans that need to be cognizant of other sectoral priorities and potential conflicts and hence need to be harmonized.Studies on China s mega-cities demonstrate that there are ways to simplify the UCC framework, quantify and evaluate indicators across sectors and use them appropriately for sustainable urban land management practices. While frameworks for carrying capacity are not the touchstone for determining efficient resource allocation, they can be useful in rationalising and improving decision-making for sustainable growth of cities; only if they are adaptable to account for variabilities over time, sectors, scale and contexts and tested for applicability through an iterative feedback loop. (Bhattacharya & Dhindaw are lead, sustainable cities and transport, and director, integrated urban planning, respectively, World Resources Institute WRI ) India Ross Centre for Sustainable Cities)