American Megacities Research Articles

Sustainability transitions require an understanding of smaller cities

AbstractAs we approach an era where more than 60% of the global population lives in cities, urban areas must be our focal point in the transition to the flourishing societies of future decades. While much attention has been paid to understanding urban consumption patterns over the past decade, the overwhelming majority of recent urban metabolism research has focused on larger cities with populations over 1 million inhabitants. Meanwhile, estimates show that more people live in urban areas with populations between 300,000 and 1 million people than in mega cities. Indeed, given their relatively small size, there are many more of these cities to study than larger cities; many more urban governments need to be informed of the solutions that are relevant to the context of their less dense populations. Our goals to decarbonize and dematerialize societies require discussions of measures that are applicable to different types of urban areas across various population scales. We take the example of the town of Reading, United Kingdom to illustrate how per capita urban metabolic flows differ within small‐ and medium‐sized cities, as well as for megacities. For example, relative to Reading, we find that there is substantial variability in energy demand for small cities (i.e., Le Mans is 150% higher) and for larger cities (50% higher for other European and North American megacities). This underscores the need to explore this under‐researched area of urban metabolism, as well as the development of a typology to enable comparisons and differentiate strategies for sustainability transitions.

Urban growth and loss of green spaces in the metropolitan areas of São Paulo and Mexico City: effects of land-cover changes on climate and water flow regulation

Urban green spaces provide ecosystem services that directly or indirectly benefit people, however, urban growth (especially in developing countries) generates the loss of these green areas and consequently of their ecosystem services. This paper aims to present the effects of land use and land cover changes in the last 30 years on two basic urban ecosystem services, water flow regulation and local and regional climate in two of main Latin American megacities (São Paulo and Mexico City). The study focuses on urban green spaces because they reduce the urban heat island effects, improve air quality, create habitats for biodiversity conservation, provide cultural services, and contribute to flooding prevention and groundwater conservation. A spatial analysis with the aid of geographic information systems was performed to assess (i) the urbanization process of the Metropolitan Areas of both cities over time; (ii) how this process generated changes in the land cover in both metropolises, and (iii) how these changes caused environmental negative impacts on ecosystem services. The loss of green areas as a consequence of urban expansion in the Metropolitan Areas of São Paulo and Mexico City changed the spatial distribution of urban heat island and increased the surface runoff, generating floods during the rainy periods. Our results suggest the urgent need for implementation of ecosystem-based spatial planning and ecological restoration of urban green areas in both studied cities to prevent further losses in ecosystem services and to improve the quality of life of urban inhabitants.

Multidisciplinary contributions towards an evolutive interpretation of bipolar disorders: Could it be the pathological drift of a potentially adaptive condition?

This paper tries to summarize the results of studies from different disciplines supporting the idea that temperamental traits, such as "reckless/hyper-exploratory" attitudes, commonly believed to be associated with psychopathology, surprisingly turn out as adaptive under specific stress conditions. In particular, this paper analyzes an ethologic line of research on primates suggesting models for a sociobiological interpretation of mood disorders in humans; a study that found high frequencies of a genetic variance associated with bipolar disorder in people without bipolar disorder but with hyperactivity/novelty-seeking traits; the outcomes of socio-anthropologicalhistorical surveys on the evolution of mood disorders in Western countries in the last centuries; surveys on changing societies in Africa and African migrants in Sardinia; and studies that found higher frequencies of mania and subthreshold mania among Sardinian immigrants in Latin American megacities. Although it is not unequivocally accepted that an increase in the prevalence of mood disorders has occurred, it would be logical to suppose that a nonadaptive condition should have disappeared over time; mood disorders, on the contrary, persist and their prevalence might have even increased. This new interpretation could lead to counter-discrimination and stigma towards people suffering from the disorder, and it would be a central point in psychosocial treatments in addition to drugs. The aim is to hypothesize that bipolar disorder, strongly characterized by these traits, may be the result of the interaction between genetic characteristics, not necessarily pathological, and specific environmental conditions, rather than a mere product of an aberrant genetic profile. If mood disorders were mere nonadaptive conditions, they would have disappeared over time, however, their prevalence, paradoxically, persists if not even increases over time. The hypothesis that bipolar disorder may result from the interaction between genetic characteristics, not necessarily pathological, and specific environmental factors, seem more credible than considering bipolar disorder as a mere product of an aberrant genetic profile.

Forest fires and impacts of COVID-19 lockdowns on air quality in four Latin American megacities

Latin America, as other regions in the world, imposed mobility restrictions to tackle the COVID-19 pandemic. Although recent research has analyzed the effect of mobility restrictions on air quality in several regions, a scarce literature explores the causal effects of the lockdowns in Latin America at a city scale whose results may guide local policymaking. This article, based on a quasi-experimental approach, estimates the causal short-term impacts of lockdowns on air quality considering the influence of forest fires on pollution in four megacities in Latin America (Bogotá, Mexico City, Santiago, and Sao Paulo). Results show that nitrogen oxides and carbon monoxide consistently declined (from 16% to 68%), nevertheless, fine particles rarely decreased across cities. Only Bogotá exhibited an overall reduction in fine particles (45% for PM2.5). Mexico City obtained the lowest reduction in pollutants, whereas Bogotá outperformed other cities in several pollutants. Evidence from mobility statistics supports the decrease in air pollution by a reduction in driving, transit use, and other mobility indicators.

Atmospheric particulate pollution in South American megacities

Air pollution is one of the major problems caused by urban growth, and both industrial and automobile emissions have been the main causes of air quality deterioration in cities since the beginning of the 20th century. Atmospheric pollution is the largest single environmental risk for health, causing about 7 million human deaths per year. On a global scale, developing countries are major contributors to air pollution due to their rising economies, with rapid industrial and population growth combined with poor emission controls. In South America, there are five megacities (Bogotá, Buenos Aires, Lima, Rio de Janeiro, and São Paulo) with over 10 million people potentially contributing to wide-ranging environmental consequences. Atmospheric particulate matter (APM) plays a leading role in the transport of trace metals and metalloids through the atmosphere and are chemical markers of air quality. The presence of these pollutants in APM has a detrimental effect on both air quality and human health. In this review, we provide an integrated assessment of hazardous metals and metalloids in the fine and coarse APM fractions, focusing on the South American megacities. We identified the current state of research for Ba, Cd, Cr, Cu, Mo, Ni, Pb, Pd, Pt, Rh, Sb, Sn, V, and Zn and summarized the findings in the 21st century. The findings of this review highlight that despite the phasing out of leaded gasoline, Pb continues to be a metal pollutant with one of the highest atmospheric emission rates, mainly due to vehicular pollution. The megacities from Brazil and Argentina were, by far, those with the highest number of studies performed; however, updated research is needed for the five megacities, including specific studies on fine and ultrafine particulate matter fractions as these pose serious human health issues. Urban agglomerations denoted sustained increases of most metals over time that is indicative of deteriorating air quality. Nickel and Cd concentrations in megacities from Argentina, Brazil, and Colombia, as well as Pb in one study from Colombia, were found to have exceeded international air quality guidelines.

A Regression Analysis of the Carbon Footprint of Megacities

Urbanization and climate change are two major issues that humanity faces in the 21st century. Megacities are large urban agglomerations with more than 10 million inhabitants that emerged in the 20th century. The world’s top 100 economies include many North and South American megacities, such as New York, Los Angeles, Mexico City, Sao Paulo and Buenos Aires; European cities such as London and Paris; and Asian cities such as Tokyo, Osaka, Seoul, Beijing and Mumbai. This paper addresses a dearth of megacity energy metabolism models in the literature. Cross-sectional data for 36 global megacities were collected from many literature and Internet sources. Variables included megacity name, country and region; population; area; population density; (per capita) GDP; income inequality measures; (per capita) energy consumption; household electricity prices; (per capita) carbon and ecological footprint; degree days; average urban heat island intensity; and temperature and precipitation. A descriptive comparison of the characteristics of megacities was followed by ordinary least squares with heteroskedasticity-robust standard errors that were used to estimate four alternative multiple regression models. The per-capita carbon footprint of megacities was positively associated with the megacity GDP per capita, and the megacity ecological footprint; and negatively associated with country income inequality, a low-income country dummy, the country household electricity price, and the megacity annual precipitation. Targeted policies are needed, but more policy autonomy should be left to megacities. Collecting longitudinal data for megacities is very challenging but should be a next step to overcome misspecification and bias issues that plague cross-sectional approaches.

On the Use of Hedonic Price Indices to Understand Ecosystem Service Provision from Urban Green Space in Five Latin American Megacities

Latin American (LA) megacities are facing enormous challenges to provide welfare to millions of people who live in them. High rates of urbanization and limited administrative capacity of LA cities to plan and control urban growth have led to a critical deficit of urban green space, and therefore, to sub-optimal outcomes in terms of urban sustainability. This study seeks to assess the possibility of using real estate prices to provide an estimate of the monetary value of the ecosystem services provided by urban green space across five Latin American megacities: Bogota, Buenos Aires, Lima, Mexico City and Santiago de Chile. Using Google Earth images to quantify urban green space and multiple regression analysis, we evaluated the impact of urban green space, crime rates, business density and population density on real estate prices across the five mentioned megacities. In addition, for a subset of the data (Lima and Buenos Aires) we analyzed the effects of landscape ecology variables (green space patch size, connectivity, etc.) on real estate prices to provide a first insight into how the ecological attributes of urban green space can determine the level of ecosystem service provision in different urban contexts in Latin America. The results show a strong positive relationship between the presence of urban green space and real estate prices. Green space explains 52% of the variability in real estate prices across the five studied megacities. Population density, business density and crime had only minor impacts on real estate prices. Our analysis of the landscape ecology variables in Lima and Buenos Aires also show that the relationship between green space and price is context-specific, which indicates that further research is needed to better understand when and where ecological attributes of green space affect real estate prices so that managers of urban green space in LA cities can optimize ecological configuration to maximize ecosystem service provision from often limited green spaces.

Chemical composition and source apportionment of PM10 at an urban background site in a high–altitude Latin American megacity (Bogota, Colombia)

Bogota registers frequent episodes of poor air quality from high PM10 concentrations. It is one of the main Latin American megacities, located at 2600m in the tropical Andes, but there is insufficient data on PM10 source contribution. A characterization of the chemical composition and the source apportionment of PM10 at an urban background site in Bogota was carried out in this study. Daily samples were collected from June 2015 to May 2016 (a total of 311 samples). Organic carbon (OC), elemental carbon (EC), water soluble compounds (SO42-, Cl-, NO3-, NH4+), major elements (Al, Fe, Mg, Ca, Na, K, P) and trace metals (V, Cd, Pb, Sr, Ba, among others) were analyzed. The results were interpreted in terms of their variability during the rainy season (RS) and the dry season (DS). The data obtained revealed that the carbonaceous fraction (∼51%) and mineral dust (23%) were the main PM10 components, followed by others (15%), Secondary Inorganic Compounds (SIC) (11%) and sea salt (0.4%). The average concentrations of soil, SIC and OC were higher during RS than DS. However, peak values were observed during the DS due to photochemical activity and forest fires. Although trace metals represented <1% of PM10, high concentrations of toxic elements such as Pb and Sb on RS, and Cu on DS, were obtained. By using a PMF model, six factors were identified (∼96% PM10) including fugitive dust, road dust, metal processing, secondary PM, vehicles exhaust and industrial emissions. Traffic (exhaust emissions+road dust) was the major PM10 source, accounting for ∼50% of the PM10. The results provided novel data about PM10 chemical composition, its sources and its seasonal variability during the year, which can help the local government to define control strategies for the main emission sources during the most critical periods.

Drivers of biodiversity patterns in parks of a growing South American megacity

How urban habitats contribute to biodiversity conservation is a key challenge in a rapidly urbanising world. Urban parks can provide important habitats for native species, but previous studies are geographically biased; fast growing megacities, in particular in South America, are clearly understudied. To assess habitat functions and underlying drivers in parks of Santiago de Chile, we analysed the assemblages of wild growing plant species in two ubiquitous park habitat types (grasslands, wooded areas) in 15 parks (150 plots) along an urban-rural gradient. We first used linear contrasts to compare species richness, beta diversity and the proportion of introduced species. We then tested for the explanatory value of environmental variables operating at different spatial scales (plot, park, urban matrix). Unlike in most previous studies, biodiversity patterns were not related to the position of the parks on the urban-rural gradient. Introduced species, mostly from Europe, generally dominated both habitat types (>90 %). Socio-economic (population growth or density), but not spatial, variables were retained in most models. Maintenance intensity was most influential in predicting species assemblages, complemented by park age in wooded areas. A high proportion of European grassland species indicates a trend of homogenisation in park grassland at a cross-continental scale. We conclude that habitat functions of urban parks for native species that have been mainly demonstrated for Europe cannot be generalised to South American megacities. This highlights the need for innovative and locally appropriate conservation approaches (e.g., re-introduction of native species) to foster biodiversity functions in urban parks of South American megacities.

A comparative analysis of megacity expansions in China and the U.S.: Patterns, rates and driving forces

Research on physical characteristics and land-cover dynamic changes of megacities over time provides valuable insights for effectively regulating urban planning and management. This study conducts a comparative analysis of 30-year urban expansion patterns and rates among three metropolises in China (Beijing, Shanghai, and Guangzhou) and another three in the USA (New York, Los Angeles, and Chicago) based on time-series impervious surface area (ISA) data extracted from multitemporal Landsat images using the linear spectral mixture analysis approach. This research indicates significantly different urbanization patterns and rates between the Chinese and American megacities. The ISA expansion area in Chinese megacities was five times higher than that in American megacities during the past three decades. The Chinese megacities expand outward from the urban core to the periphery in a concentric ring structure, whereas the American megacities increase ISA mainly within the inner cities with patch-filling patterns. The Chinese megacities are in the development stage where population and economic conditions significantly influence urban expansion patterns and rates, but the American megacities are in the developed stage where population and economic conditions are not important forces driving the ISA expansion. The ISA intensity in the American megacities decreases constantly and smoothly, but ISA intensity in Chinese megacities decays abruptly within certain distances, depending on different cities and years. The most obvious urban expansions were between 8 and 20km in Beijing in the 1980s, between 14 and 50km in Shanghai in the 2000s, and between 8 and 18km in Guangzhou in the 1990s.

The city museum of São Paulo: a new design for city museums in the era of the megacity

The City Museum of São Paulo as subject of study and museological challenge tries explicitly to present a multidisciplinary methodology - already tested in 2003 and 2004 - that enunciates the conception of a new model of city museum, whose objective is the analysis of the great metropolis São Paulo, articulated upon the collection of contemporary items to be pursued by methods of social mobilization, maintaining a dialogue with the proper logic of a globalised world, but canonically erected over the founding precepts of sociomuseology. Focusing on territory museums, that model tries to stimulate an alternative new path that observes and interacts with the reality that is inherent to contemporaneity, to Latin American megacities, as it endeavors to understand the dynamics, as well as the problems that characterise human life in those vast and complex territories.

Air quality progress in North American megacities: A review

Air quality progress in the North American megacities of Los Angeles, New York, and Mexico City is reviewed, compared, and contrasted. Enormous progress made in North America over the last 5 decades provides a template for other megacities of the world, especially in developing countries, attempting to achieve rapid economic growth without compromising air quality. While the progress to date has been impressive, many challenges remain including the need to improve air quality while simultaneously mitigating climate change. The impact of pollutant emissions from megacities is felt long distances away from the local sources but no policy mechanisms currently exist to mitigate air quality impacts resulting from such pollution transport.

Sá, Lúcia. Life in the Megalopolis: Mexico City and São Paulo. London and New York: Routledge, 2007.

At the start of her latest book, Lúcia Sá explains the intellectual trajectory that led her to a study of the Latin American megacities of Mexico City and São Paulo by way of Mário de Andrade’s Macunaíma: “in order to recover his muiraquitã, the eponymous Mário de Andrade traveled from one end of Brazil to the other, the Amazon to São Paulo, and in a sense, having completed Rain Forest Literatures (2004), this is what I have attempted to do in this study” (x). Such a work, following one on the literatures of the Amazon, underscores Sá’s admirable commitment to exploring the literary and cultural extremes of her native Brazil, while at the same time incorporating other materials that make a more comparative discussion with internal indigenous cultural elements or other Latin American societies possible.

A Watershed in Our Profession

As ground water professionals, we have reached a watershed in our profession. Over the past 50 years, ground water hydrology has developed and matured into a quantitative and sophisticated discipline. The scientific maturity of ground water hydrology is such that researchers are now extending old subject boundaries into interdisciplinary areas such as ground water dependent ecosystems, contaminant biogeochemistry, and societal drivers for ground water use. Are we about to see a gradual deemphasis of ground water skills and decreasing interest as new fields rise to prominence? No, on the contrary; I believe we are just embarking on a path that will reinforce and reinvigorate ground water hydrology as a discipline. In fact, it is likely that our discipline will soon be regarded as fundamental to our very survival. Our world is changing. United Nations statistics show that humans are congregating in urban centers at an astonishing rate. In 1950, the percentage of humanity living in urban centers was 29%; now it is 49% and is expected to reach approximately 60% in the next two decades. Over the same period, global population will climb from 2.5 billion to approximately 8.2 billion, and almost 5 billion people will live in urban centers by 2030. Yet the total amount of accessible fresh water on the earth, held in lakes, rivers, and aquifers, is constant. The United Nations estimates that, currently the global population appropriates 54% of the accessible fresh water, and this fraction will exceed 70% by 2025. With almost 70% of this fresh water demand currently expended on agriculture, it is clear that the amount of accessible fresh water available for domestic use is disturbingly close to a limit. If we assume that the projections are correct, then the need for change in the way we regard our water resource is clear—both quantity and quality are paramount. Even developed nations are now experiencing water shortages, and an estimated 6000 people die each day from drinking contaminated water. Urbanization is not a guarantee of population health. The incredible growth of Asian, African, and South American megacities has generated intractable problems of ground water supply, management, and regulation. As one example, the population of Karachi in Pakistan has grown almost fiftyfold to at least 16 million in the past five decades and the water infrastructure is collapsing. Arsenic and fluoride are found in ground water beneath large areas of densely populated Africa, Asia, and elsewhere, threatening the health of hundreds of millions. In some urban locations, there is rapid transmission of effluents to ground water and potential for hazardous chemical species to persist through the water treatment and disposal trains, thereby increasing in concentration in successive passages through the urban water cycle. Of particular concern here are pharmaceuticals and endocrine disruptors, which may affect a range of life forms at trace concentrations. As fresh water in easily accessible surface water systems is exploited, ground water will become the priority drinking water resource for the future. This simple and expedient choice of water resource will have profound impacts on our relation to water. To use water sustainably in our heavily urbanized future, ground water resources must be protected and managed now through every step of the urban water cycle. Failure to do so may render valuable supplies unusable just when we need them the most. The global call for ground water professionals will only increase. Better identification and characterization of ground water assets will become a growth industry as urban centers proliferate across the world. Application of geospatial characterization techniques from other disciplines may boost productivity and reduce costs associated with this major ground water exploration effort. At the same time, ground water professionals will be required to develop new levels of expertise in assessing ground water quality to secure and manage resources of potable drinking water in heavily urbanized areas where sources of contamination are many and varied. The focus of ground water research will shift from exploitation of supply to sustainability and protection of human and environmental health. Communities around the world will demand high-quality scientific and engineering advice as they deal with the demographic and environmental consequences of expanding urbanization in the face of water limitation. Ground water professionals must be ready to embrace the expanding challenges ahead. This represents a great opportunity for our profession, but the global consequences of failure are unthinkable. It is not a time to be disinterested.

A Study on Urban Transportation Evolution in Latin American Mega-Cities

A Study on Urban Transportation Evolution in Latin American Mega-Cities

A Walk in the Invisible City

This essay discusses the performative interventions of the contemporary Belgian artist Francis Alys in Mexico City and how they create a critical focus on urban reality in the Latin American mega-cities, and outline ways of intervention and interaction in the modern disassociation of the city’s economical, social, and cultural levels, taking up the challenge to suggest their unity through imagination and art.

Globalization, regional development, and mega-city expansion in Latin America: Analyzing Mexico City’s peri-urban hinterland

This paper examines the transformation of urban space in the peri-urban areas of Latin American mega-cities, further exacerbating the multi-jurisdictional political divisions that cover a single urban entity. This is against the backcloth of a sharp decline in metropolitan growth rates, absolute population loss in the city center, and an alleged “polarization reversal” of national urban patterns. It argues that previous approaches have failed to recognize that globally and nationally-derived economic development processes are often vested in these meta-urban peripheries. Using Mexico City as an example, the authors propose a new generic methodology that will allow for a broader definition and analysis of mega-city and large metropolitan development. Data are presented within this new framework that help to unpack the demographic, economic and land-use changes that are taking place in Mexico City’s broader urban area. Much of the contemporary vibrancy and dynamics of Mexico City’s metropolitan development are occurring in “hot-spots” in the extended periphery, which, to date, have rarely been considered an integral part of the mega-city. Yet these areas are also some of the principal loci of contemporary globalization processes.

Gated Communities in Latin American Megacities: Case Studies in Brazil and Argentina

Within recent years, the expansion of gated communities has become an increasingly important element in the changing Latin American megacities and their suburban areas. In this paper, the internal ...

Gated communities in Latin American megacities: case studies in Brazil and Argentina

Gated communities in Latin American megacities: case studies in Brazil and Argentina

Contemporary issues in the government and administration of Latin American megacities

This paper is the first to systematically analyze and compare the structures of city governance and administration for seven major cities in Latin America, four of which are megacities (population of over 10 million), and three others are large national capitals. U.S. and U. K. models of city administration are reviewed as baseline models against which differences in Latin American may be explored. Structures of Government in Latin America show several important features and trends: 1) the lack of metropolitan (cross jurisdictional) authority; 2) the existence of strong mayors and weak councils"; 3) high levels of partisanship; 4) overlapping rather than interlocking bureaucracies; 5) pressures towards the privatization of city services, but continuing tension over the desirability of public versus private control; 6) greater fiscal responsibility and autonomy; and 7), a continuing marginalization of public participation in megacity governance.In spite of these features, many cities throughout the region (regardless of whether they are megacity size or national capitals), are actively intensifying their efforts to develop more effective, accountable and democratic governance structures.