Low-carbon cities are those that to be urbanized, operated and maintained release relatively low carbon amounts and their equivalents into the atmosphere (Wang & Prominski, 2016; City of Copenhagen, Technical and Environmental Administration, 2012; Drake, 2014; Chase & Lawrence, 2010; La Roche, 2012). A low-carbon city involves smart planning and sustainable design, by means of which it is sought to reduce and mitigate the environmental impacts that cities generate over their entire life cycle.

To understand the life cycle of a city, we must separate the cities in their various infrastructure parts, as each of these components has its own service life and durability and they also depend on their historic and economic period. Cities are known to be complex, dynamic, and highly integrated systems that evolve over time and separating their lifecycle phases and predict their service life accurately can be complicated (McPhearson, Haase, Kabisch & Gren, 2016). Figure 1 summarizes the life cycle of an average Mexican city.

Figure 1 Figure 1 Life cycle of cities Source: author’s own elaboration

The problem of fast and uncontrolled urbanization (urban sprawl) partially lies in the inoperative design of neighborhoods, linked to bad planning in the use of urban land, as well as in other demographic problems such as countryside-city migration; economic ones, lack of employment and food; and even cultural and social, for instance discrimination of rural culture and habits and customs of indigenous people, which is in fact, the origin of most of the urban population nowadays, as before 2010 most of the population was located in rural zones and almost all urban population has urbanized (United Nations, 2008).

The aim of this document is to generate a prototype or proposal of urban cluster design (based on building by blocks) that works as a design pattern to plan low-carbon cities under the smart urban planning criterion, propitiating solutions that generate employment, food and small and mid-scale energy production in the cities, thus helping regional sustainable development and improving the quality of life of many urban inhabitants in the present and the near future.

In Mexico, as everywhere, the traditional model to plan cities has concentrated the population in inefficient and unproductive urban and semi-urban zones that deepen social inequality and generates pollution and environmental impacts that put at risk many people to climate change (Molina, 2014).

Most of the cities in the world are based on an economy that consumes fossil fuels with heavy carbon emissions into the atmosphere, which cause the widely known problems of global warming and climate change (Cheung & Fan, 2013; Van der Werf et al., 2009; Bin Marsono & Balasbaneh, 2015; Fouquet et al., 2015; Centro Mario Molina, 2014). On the other side, the planning and design of cities have a preponderant role in mitigating and reducing carbon footprint at local and global scales; this way, it is necessary to propose a radical change in the way cities are designed and planned in order to counteract the effects of climate change, which it can summarize in the following points:

Air, soil and water pollution.

There are worrying data on the global urbanization levels required in the near future; for instance by 2035, China will need to build new cities to hold about 350 million people, only in 20 years’ time (McKinsey & Company, 2009).

The following questions are partially or fully answered in the present research work:

Which sector in Mexico produces the most carbon emissions into the atmosphere?

A priory, we can anticipate our answers to the previous questions. The first answer to this set of questions is that urbanists and architects shall design and plan low-carbon cities with low environmental impacts as a general rule. Secondly, urban development plans must consider suitable and productive land uses, both in the urban and rural environments. Subsequently, architects and urbanists should know cities are complex systems and these subdivide in sub-systems, each with a specific function that will have an influence on the rest of the system and an impact on the subsystems. Some of the most important of these sub-systems are:

Urban morphology (shape, layout and structuring).

The hypothesis which the present work is based upon is that smart urban planning should be supported on the design of low-carbon urban clusters (Figure 2) composed of neighborhoods with various land uses (at an urban-architectural or meso-scale) arranged in such manner that they reduce the environmental impacts in the cities, therefore each urban and architectural configuration has a determinate level or degree or carbon footprint.

It would be important and to complement the hypothesis, that these blocks edified from urban clusters incorporate in their urban land uses, those typical of the rural sphere such as agriculture and small and mid-scale energy production, in views of offering partial solutions to the largest problems of urban zones, i.e., green energies and food production activities.

Thereby there would be a new sort of city, which we have called rural-city or ruralized city; it is a low-carbon one and incorporates smart solutions for the development of cities, mainly in developing countries such as Mexico and Latin America.

The consumption of energy from fossil fuels to build and operate all the cities in the world produces approximately 50 % of the total harm from global warming (Van der Werf et al., 2009; Bin Marsono & Balasbaneh, 2015; Fouquet et al., 2015), so architects and urbanists shall face and solve these problems at various scales, from the architectural or micro scale to a metropolitan or macro scale so that there can be a global-scale incidence.

Figure 2 Figure 2 Urban cluster according to certain land uses Source: author’s own elaboration

Besides, land uses markedly influence the urban dynamics of the cities as well. They can increase or reduce to a large extent the environmental, economic, migratory effects and also those from “urban metabolism” proper to the cities; this understood as the physical study of the resources flows required to maintain the economy of a city (Fernandez, 2014). This is to say, the way in which resources are consumed in a city or human settlement, therefore these land uses have to be controlled so that they do not interfere with the growth of the cities and with the human activities there performed.

The aim of the present document is to generate and design a low-carbon urban cluster that works as a design pattern for the smart planning of cities. The object of the study was the constructed urban environment, limited to Mexican and Latin American cities, which have similar problems and defects.

The approached problem, as already mentioned in the introduction, was that frequently cities grow in a disordered manner, and at the same time this generates a number of problems in the demographic structure of the cities, as it is the case of countryside-city migration, lack of employment and food and the decrease of the quality of life in the cities, in addition to all the environmental impacts, related to soil, air and water that cities generate, accompanied by carbon emissions into the atmosphere. Therefore, in this study the dependent variable or response variable is the amount of carbon dioxide emissions emitted by the cities; and the control variables or independent variables could be different resources flows that pass through the city for its operation and maintenance, also measured in carbon dioxide emissions during a certain time of service life of the city, urban cluster or neighborhood.

Formula 1 can express the estimation of carbon dioxide emitted by the cities or urban clusters as an indicator of its urban metabolism:

(1)

Where:

ECO₂ = Estimation of Carbon Dioxide emitted by the cities, urban clusters or neighborhoods (CO₂ tons);

DSL= Design Service Life of a particular city, urban cluster or neighborhood, etc. (years);

i= Index;

F1-F9= Summands (resources flows);

Resources flows (CO₂ tons) as factors influencing the Estimation of Carbon Dioxide emitted by the cities:

F1= Self-consumption;

F2 = Electric generation;

F3 = Manufacture and Construction industry;

F4 = Transport;

F5= Commerce;

F6 = Residential;

F7 = Agricultural;

F8 = Mining and Carbon handling;

F9 = Oil and Gas industry.

The particular method utilized to reach a low-carbon urban design proposal was to first limit the urban space of the cities at an urban-architectural or meso-scale in which a model or pattern called urban cluster was generated to later apply a number of environmental design strategies (Table 1) and smart design criteria were used (strategies to design low-carbon clusters).

Strategies of sustainable design previously generated by the author of this document by means of revising various environmental design models, mainly the American LEED Neighborhoods model, the United-Kingdom Breeam Communities model and CEV Code by Mexican Conavi (Comisión Nacional de Vivienda, 2015) [National Housing Commission]. In views of proposing an own model of sustainable design of cities in Mexico to incorporate into the cluster aspects referring to the sustainable management of the site, water, energy, materials, waste and comfort, thus propitiating an environmental design.

On the other side, the design strategies for low-carbon urban cluster have also been proposed from revising models, methods, regulations and information that answered the following question: how can we reduce the consumption of resources in the cities to improve their metabolism without decreasing the inhabitants’ quality of life? This way, arose the idea of designing an urban pattern that sets the example to plan cities with a low-carbon footprint without compromising their inhabitants’ quality of life.

Subsequently, a low carbon cluster proposal was designed through the following urban and architectural design criteria (strategies and design key points):

The first and the one with the heaviest environmental impact, is the energy item and impacts produced by the use, operability and maintenance of infrastructure, mainly: electricity, gas, water and generation of solid and liquid waste.

Two direct solutions that are proposed to reduce resource consumption are: 1) produce energy inside the cities, decrease energy and water consumption, and reduce both solid and liquid waste; 2) in order to improve the urban “metabolism” in the cities, incorporate urban agriculture and food production in the cities at an urban-architectural or meso-scale.

Vertically densify urban infrastructure and equipment (construction), including of course: housing, commerce, government, industry, education and other services by means or urban blocks to decrease the traditional size of large, horizontal and sprawled cities.

Not all the cities and countries produce a similar carbon footprint, because they are all different and each has its own urbanization, maintenance and operation mechanisms, and the “metabolism” varies or resource consumption changes depending on the size and characteristics of the city.

For example, the countries that produce the most CO₂e (CO₂e understood as greenhouse effect emissions such as: methane, nitrous oxide, hydro-fluoro-carbons, etc., which equal determinate amounts of carbon dioxide emissions) are: China the country with the heaviest CO₂e emissions from energy consumption, producing only in 2012, 8,106 million metric tons (Department of Energy, 2015); followed by the United States with 5,270 million metric tons; India, 1,831 million metric tons; Russia, 1,782 million metric tons; Japan, 1,259 million metric tons; Canada, 551 million metric tons; Brazil, 500 million metric tons; Mexico, 498,971 million metric tons in 2012, not counting emissions from the forest sector nor changes in land use (Department of Energy, 2015).

Indeed, most of these countries hold the largest cities in the world, namely: Shanghai (China), New York (US), Delhi (India), Tokyo (Japan), Mexico City (Mexico) (United Nations, 2008) etc.

Given that traditional models used for planning and design cities cannot deliver low carbon cities then we must now focus to transform our economies based on fossil fuels to low-carbon economies, which also should be included environmental services in the cities and towns that focus on local food production and alternative energy generation through proper planning of land uses.

On the other hand, trying incentives from governments at all levels to design and plan green infrastructure in cities. This will not only support sustainability in cities but it is a smart way to mitigate environmental impacts in rural areas too, improving the quality of life of the people on both sides.

As partial solution urban planning should be supported on the design of low-carbon urban clusters composed of neighborhoods with various land uses (at an urban-architectural or meso-scale) arranged in such manner that they reduce the environmental impacts in the cities, therefore each urban and architectural configuration has a determinate level or degree or carbon footprint.

Neighborhoods and blocks edified from urban clusters incorporate in their urban land uses, those typical of the rural sphere such as agriculture and small and mid-scale energy production, in views of offering solutions to the largest problems of urban and rural zones.

The design of urban clusters of low carbon could give partial solutions to gradual change from high carbon cities to low carbon cities, especially in economies that base their development on fossil fuels such as Mexico and many countries in the world.

Cities are complex systems that evolve over time and it becomes difficult to separate their life cycle phases and predict their durability and service life accurately.