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Part I
Introducing and understanding the process
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1 Is urban expansion a problem?
Ciro Gardi
Introduction
Every mark traced on the territory by a new road or highway assumes the meaning of the ditch ploughed by Romulus, imposing the boundaries of the rising ancient Rome: another piece of land to be filled by buildings, generally low-quality buildings lacking aesthetics. Our approach to the use of land is much the same as the American pioneer, even 200 years later, even in crowded continents like Europe or China.
The evident environmental failure of liberal, and also communist, economic systems is caused essentially by the limits of the monetary aspects involved in the production of goods and services, ignoring the externalities (or, in the best case, under evaluating them). The globalization process that was announced as the panacea for these problems resulted in an unlimited amplification of environmental issues.
It is evident that if we consider only the direct costs (production and transport for instance) associated with the production of a good in China, for example (with labour and social costs one tenth that in Europe or North America), the market competition will be very unfair. To perform an environmentally correct evaluation, in addition to the evident, direct costs, we should add the impact associated to the extraction, production and use of fuel needed for the transport of the goods. This disproportional competition, and incorrect evaluation of environmental costs, has resulted in unsustainable development processes and severe environmental impacts.
The uncontrolled, and often unmotivated urban sprawl is an example of this inaccurate evaluation of the environmental consequences of our actions and decisions. The âfloodingâ of concrete and asphalt is progressing, with little consideration of the irreversible consequences of these practices. Degradation of the landscape, increase in traffic and air pollution, flooding events, the loss of agricultural and natural areas, have been ineffective in raising awareness and stimulating action to protect one of our most precious resources and our collective identity: our land. In addition to the local impacts, we then have to consider the cumulative consequences of our local actions at the global scale.
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Soil is becoming, more and more, a limited and strategic resource; increases in population and food demand and the production of biofuels, are driving an increase in biomass demand, and consequently demands on agricultural lands. At the same time, urban expansion and the intensification of agricultural practices, are causing the degradation of agricultural soils and pushing agriculture onto marginal lands or into natural habitats.
What is happening to the soil is a representation of the frequent âtragedies of commonsâ (Hardin, 1968), that are replicated every day, in every corner of the planet, for water, biodiversity, climate, etc.
There is, however, increasing attention to these global environmental issues in the public opinion (still too limited), driving also changes in the international and local political agenda.
New concepts, such as âclimate justiceâ (Robinson and Miller, 2009), or âsoil securityâ (McBratney et al., 2014), have been introduced, and a new deal and renovated environmental commitment by the Catholic Church, started by Pope Francesco, are marked by the recent encyclical Laudato si (Francesco, Pope, 2015), in which the Pope is waking humanity up to care for the planet.
Analysis of global land cover maps, e.g. Global Land Cover 2000, indicates that urban areas were covering 0.2 per cent of the Earthâs land surface at the end of the previous millennium. This number can be considered relatively small and, therefore, not necessarily a major threat to our planetâs ecosystem services. Let us focus, however, on one of the most pertinent ecosystem services, at least from an anthropocentric point of view: food production. If we consider the potential threat represented by urban expansion on food productivity, it becomes clear that the topic merits a more in-depth assessment.
With regard to estimating the extent of urban areas/artificial surfaces, it is possible to ascertain values from other global land cover maps, most of them derived from satellite images. Schneider et al. (2009) produced a land cover map, derived from Modis images, and focused on urban areas. Based to this map, they provided a very accurate estimate that the extent of urban areas in 2000 was 657,000 km2. Values obtained from other data sources, reviewed in the same paper, ranged between 276,000 km2 up to 3,524,000 km2. These values highlight the importance of reliable data in understanding urban growth processes.
Urban expansion dynamics in the world
Over the past few decades, human activities have reached such intensity that they represent the most significant factor modifying our planet. Among human activities, the processes related to urbanization most certainly play a major role.
Urbanization can be determined by several factors: population growth, a positive balance between immigration and emigration, the economic growth of a given area, and speculation processes where the expansion of built-up areas is not related to the needs of increasing residential, commercial or industrial infrastructures.
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At the global level, especially with regard to developing countries, demographic pressures and the migration of rural populations towards urban centres are the main drivers of urban expansion.
The global urban population increases by 200,000 every day, amounting to 70 million people every year that become part of the Earthâs urban centres.
Currently, the urban population represents approximately 53 per cent of the total human population, and it is expected that by 2050 this proportion will reach 70 per cent. It is considered that 60 per cent of urban growth is determined by the demographic growth of urban populations, while 40 per cent is determined by processes of migration and reclassification of land uses (with the expansion of urban areas).
We know that the first urban centres were associated with the introduction of agricultural practices, in the fertile crescent,1 and with our ability to produce surplus food that would allow the maintenance of a certain proportion of the population not directly engaged in agriculture. This is how the first cities in the Middle East, the Mediterranean, Asia and South America were established. The earliest signs of human aggregation, in the form of rural villages, dates back to 8500 bc, and the first city that we know of is Jericho, whose construction is attributed to 8000 bc.
Following the first signs of urbanization we enter the modern era, which is commonly divided into three phases:
⢠The first phase of urban growth in the modern era coincides with the important innovations in energy production technologies and, therefore, with the industrial era. From 1750 to 1950 Europe, North America and some areas of Asia were the centres of attention. Since then we have witnessed the birth of a new urban and industrial society involving significant population growth. In 1950 there were two megacities in the world, with more than 10 million inhabitants (New YorkâNewark, USA, and Tokyo, Japan).
⢠The second phase is represented by the rapid growth of urban areas in developing nations, where population growth and urbanization are usually accompanied by economic growth. This second phase, which is currently underway, is developing at a much faster rate than the previous one.
⢠The third phase is characterized by extremely rapid growth of urban areas, occurring in countries with fast growing economies, where rapid growth of the Gross Domestic Product (GDP) is associated with urbanization processes and/or demographic growth.
As of 2014, there were 488 cities in the world with a population of more than 1 million inhabitants, and 28 urban areas classified as megacities, as characterized by a population of over 10 million inhabitants (Table 1.1). It is expected that within 15 years, 13 additional cities will be added to the list of megacities: Ahmadabad, Bangalore, Chennai, Hyderabad (India), Bangkok (Thailand), Bogota (Columbia), Chengdu (China), Dar es Salaam (United Republic of Tanzania), Johannesburg (South Africa), Lahore (Pakistan), Lima (Peru), Luanda (Angola), and ThĂ nh Pho Ho ChĂ Minh (Vietnam).
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Table 1.1 Past, actual (2014) and predicted population of the worldâs 28 megacities
Source: UN (2015).
Note: Cities are ranked according to the actual population.
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The process of growth of urban agglomerations, also known as urban sprawl, can be analysed from many points of view: social, economic, environmental; however, the aim of this discussion is limited to the assessment of urbanization with regard to its direct impacts on a limited and non-renewable resource, such as soil.
The global picture
In 2008, for the first time in history, the urban population reached 50 per cent of the Earthâs total human population (Figure 1.1). It could be argued that a limit, which is not only psychological, has been exceeded.
From the graphic in Figure 1.1 we can see that the projections indicate that, while from 2020 onwards the rural population will begin to decline, the urban population will continue to grow and by 2050 the rural population will represent just one-third of the total (United Nations Department of Economic and Social Affairs, 2008). It is clear that the environmental impacts resulting from such a radical change will be enormous, albeit difficult to assess and predict with accuracy. Considering only the flows of matter and energy necessary to sustain an urban ecosystem, and the consequent production of waste and disposal thereof, we have an indication of the dimensions and the type of problems that will need to be addressed in the future.
If we consider the organic matter cycle, it is easy to see how much more balanced and sustainable a widespread system (rural area) would be, in which the production of biomass (food, fibre, biomass for energy production) and its decomposition take place in a distributed way throughout the territory. In contrast, in a megalopolis, fluxes of thousands of tons of organic matter entering the urban ecosystem are then disposed through artificial processes (landfills, incineration, anaerobic digestion) in a concentrated way.
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Table 1.2 Population dynamics in some Asian urban agglomerations
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From the point of view of land use, processes of urban growth and the urbanization of rural populations involve a net increase in impervious surfaces (sealed areas), increasing the consumption of land through a phenomenon known as âland takeâ.
If we consider, for example, areas with strong economic growth in some Asian cities, we can observe a much higher expansion of urban areas, which is not correlated to the increase in the resident population (Table 1.2). The growth of city populations considered increased at an average of 23 per cent in the period 1990â2000, while the average growth of the urban areas during the same period amounted to 80 per cent.
It seems clear then that the growth of urbanized areas is not ...
