World's Megacities Research Articles

Changes to Peroxyacyl Nitrates (PANs) Over Megacities in Response to COVID‐19 Tropospheric NO2 Reductions Observed by the Cross‐Track Infrared Sounder (CrIS)

AbstractThe COVID‐19 pandemic perturbed air pollutant emissions as cities shut down worldwide. Peroxyacyl nitrates (PANs) are important tracers of photochemistry that are formed through the oxidation of non‐methane volatile organic compounds in the presence of nitrogen oxide radicals (NOx = NO + NO2). We use satellite measurements of free tropospheric PANs from the Suomi‐National Polar‐orbiting Partnership Cross‐track Infrared Sounder (CrIS) over eight of the world's megacities. We quantify the seasonal cycle of PANs over these megacities and find seasonal maxima in PANs correspond to seasonal peaks in local photochemistry. CrIS is used to explore changes in PANs in response to the COVID‐19 lockdowns. Statistically significant changes to PANs occurred over four megacities: with decreases over Los Angeles and Delhi, and increases over Mexico City and Beijing in the winter. Our analysis suggests that large perturbations in NOx may not result in significant declines in NOx export potential of megacities.

Development at the cost of unsustainable degradation of wetlands: Unraveling the dynamics (historic and future) of wetlands in the megacity Dhaka

Despite the recognized role of wetlands in providing ecological benefits for human wellbeing, ∼70% of global wetland ecosystems have been destroyed since the 1990s. Further intensive studies revealed that 3.4 million km2 of natural wetland has declined since 1700. In particular, wetland habitats in the world's megacities have been replaced unsustainably by faster economic, urban, and population growth, and have received less attention in research and policy. However, wetlands degradation in the megacities of developing countries is not quantified and the trends of Land Surface Temperature (LST) are not well understood. Therefore, we are making our first attempt to unravel the historical and future spatiotemporal dynamics of wetlands and the trends of LST in the megacity of Dhaka. The results show that Dhaka lost ∼69% of wetlands and LST has increased between 3.44°C and 9.35°C from 1990 to 2020. An environmental Kuznets curve analysis implies that the point has not yet been reached for wetlands when economic development feeds back to the sustainability of the environment. This assumption coincides with our model-based prediction, as respectively ∼74% and ∼90% of wetlands area of Dhaka city will be decreased by 2050 in Business as Usual (BAU) and development scenarios, whereas, ∼66% of wetlands area will be decreased under conservation scenario over the time period of next 30 (2020 to 2050) years. Our findings suggest that it will be incredibly challenging to restore wetlands to their 1990s condition. Efforts to preserve them should be made, as they potentially provide a nature-based alternative for coping with wetland sustainability and climate change.

Assessing Water Quality Spatial Heterogeneity from Multiple Pollution Sources in the Boung Cheung Ek Wetland, Phnom Penh, Cambodia

Phnom Penh, the capital of Cambodia, as with many other world megacities, is exposed to multiple major ecological and environmental hazards. Without a proper wastewater treatment facility, it is difficult for local residents to obtain a health-compliant water supply. In this study, a hybrid aggregation method using principal component analysis (PCA) and weighted means was used to calculate a water quality index (WQI) to map the water quality of the entire Boeung Cheung Ek (BCE) wetland region. We used Universal Kriging to map eight water quality parameters: DO, pH, TDS, F, Cl, NO3−, PO43−, and NH4+. The restricted maximum likelihood method was used for model fitting. Data were collected from groundwater and surface water for different rainfall seasons between March 2017 and February 2018. The principal component analysis (PCA) used to compute a water quality index (WQI) is based on the resulting dimensions of the highest variation among all water quality parameters. The results show that the northern part of the study area has a worse water quality than the southern region, which is caused by the discharge of municipal wastewater directly into the BCE wetland area. The results for different rainfall seasons also show that groundwater has a relatively better quality than surface water. The results of this analysis can serve as a supplementary study to support sustainable development goals because they might confirm the need for a wastewater treatment facility being under construction at the time of writing this article with funding from the Japan International Cooperation Agency (JICA).

The human impact of marine ecosystem imbalance: an analysis of society and ocean management

Throughout world history, truly great nations have had to find their place in the oceans. Over 40% of the global population and most of the world's megacities are located in coastal areas. The development of proper ocean management and the implementation of marine resource construction are the core strategies for national development on the world stage. Due to the increasing needs of national development, the oceans have gradually become ecologically unbalanced after enduring human exploitation. These ecological imbalances, such as marine plastic pollution, fish overfishing, and increased climate change, will eventually return to humans and pose a serious threat to human life and health. This paper discusses the desirable and undesirable interactions between the oceans and human health and the social structure of marine resource management. Besides, this paper will propose solutions to alleviate marine ecological problems as well as promote sustainable social development based on two structural analyses. The paper concludes that the relationship between human oceans should be mutually beneficial. Oceans desire to be managed and regulated by humans for their ecosystems and do not desire to be over-exploited and polluted. Humans' desire to derive resources from the oceans to meet their spiritual and health needs while not being exposed to the risks of disasters Analysis of the socio-ecological system should be used to determine options for reducing marine ecological issues while fostering sustainable social development (SES). To put it briefly, we can now strengthen policies that prioritize the health of the ocean and people, develop trustworthy relationships among stakeholders, and encourage economic incentives that alter behavior.

Influence pandemic COVID-19 on the socio-economic efficiency of urban transport systems

The COVID-19 pandemic has fundamentally changed the way people live, think and behave, especially in cities. The pandemic, without exaggeration, has affected all spheres of economic and social life, including affecting the functioning of urban transport systems, which are a multifunctional structure that ensures the mobility of the population. Taking into account the changes that have taken place during the COVID-19 pandemic, which had a significant impact on the functioning of urban transport systems, they face new challenges, including in the sphere of ensuring environmental safety and developing new types of mobility. Special attention in this paper is paid to such issues as studying the impact of a new coronavirus infection on the behavior of citizens of world megacities based on the analysis of international experience, determining the impact of a pandemic on the objective indicators of urban transport systems. Taking into account the identified patterns, the main short-term and long-term trends that have developed under the influence of COVID-19 are identified, a comparative description of the measures taken by the city authorities to control the virus is presented, and their possible consequences are analyzed. Examples of successful projects and activities implemented by city administrations in response to the pandemic are given to ensure the long-term sustainability of the development of transport systems.

Urban wildlife corridors: Building bridges for wildlife and people

Urbanization is rapidly expanding across the globe, leading to increasing threats to wildlife in and around cities. Wildlife corridors are one strategy used to connect fragmented wildlife populations; however, building wildlife corridors in urban areas remains a challenge because of the number of barriers between habitat patches and the extensive number of property owners and stakeholders involved. Successful urban wildlife corridor conservation thus requires a collaborative approach and a cohesive plan that transcends municipal boundaries. Here we demonstrate how urban wildlife corridor conservation can provide a unique opportunity to build bridges not only for wildlife but also among scientists, non-profits, government agencies, and communities. Our case study centers on the conservation of a network of wildlife corridors in one of the world's megacities, Los Angeles, and the positive feedback loop sparked by collaboration between research and non-profit work. We discuss the benefits of and challenges to building complex collaborations for the purpose of strengthening urban resilience and redesigning sustainable cities.

In pursuit of sustainability – Spatio-temporal pathways of urban growth patterns in the world's largest megacities

Governing the future growth of the world's megacities towards higher land use efficiency is important for achieving global sustainability. We have computed statistics of the urban growth modes of 33 megacities (with ten-million-plus population) worldwide for two periods (1985–2000 and 2000–2015) and performed a hierarchical cluster analysis to examine their urban growth patterns. Results reveal that urban growth has mostly occurred through edge expansion but also that its relative dominance has decreased due to the rising shares of the infilling and outlying growth modes. Based on the co-occurrence and changing dominance of these three urban growth modes over time, four pathways of urban growth patterns are identified– oscillating/ping pong, transition-to-densification, transition-to-sprawl, and extensive sprawl. The majority of megacities followed the oscillating/ping pong pathway, which is dominated by edge expansion and altered phases of infilling and outlying growth. However, by indicating a clear shift from edge expansion towards infilling as the dominant pathway of urban growth, the transition-to-densification pathway appears to be the most sustainable in terms of land-use efficiency, with ten megacities following this pathway. Overall, our results highlight the diverse mega-urban growth pathways across the world, particularly for megacities in the Global South which generally have higher growth rates.

What can Beijing learn from the world megacities on energy and environmental issues?

In order to build Beijing into a world-class harmonious and livable capital city, its energy and environmental issues deserve special attention. Considering London’s experience and achievements in tackling smog crisis, New York’s world-class city positioning and influence, and Tokyo’s geographical and cultural characteristics, these three world-class megacities are taken as examples in this study for investigating and analyzing the establishment and optimization of an urban energy system which is clean, efficient, safe, and sustainable. The urban planning strategies, planning experience, and related energy policy of these three megacities for building low-carbon cities are reviewed and their enlightenment to Beijing is discussed. The study of international cases has a certain reference effect on the energy structure adjustment and urban planning practices related to Beijing’s construction of a low-carbon city.

Energy, environmental, resource recovery, and economic dimensions of municipal solid waste management paths in Mexico city.

Growing municipal solid waste (MSW) generation is a source of environmental, economic, and social concerns, especially in developing world megacities where poor MSW practices prevail. Mexico City (CDMX), one of the world's largest megacities, daily produces∼13,073Mg of MSW whose management poses a tremendous challenge to local authorities and calls for additional research to conceive sound MSW strategies. This study evaluates the fossil energy use, GHG emissions, resource recovery, and economic cost dimensions of current and five alternative MSW paths in CDMX to compare their performance and identify more sustainable MSW practices for the megacity. Impacts and benefits from the MSW paths were modeled using 2018 MSW generation data, information supplied by local authorities, and literature values. Current MSW path consumes∼387 MJfossil, generates∼501kg-CO2e, and costs∼57 USD2018 per Mg of MSW managed while it only valorizes<33% of total MSW mostly via informal truck-picking. The alternative MSW paths considerably reduce GHG emissions (∼129-360kg-CO2e/Mg) and enhance MSW valorization (∼47-88%) though, they entail higher fossil energy consumption (447-582 MJfossil/Mg) and, in general, higher cost expenditures (43-208 USD2018/Mg). Heavy reliance on landfilling, large GHG emissions, and low MSW valorization make current MSW path in CDMX unsustainable. Incineration-based MSW paths perform better in most aspects evaluated but their high costs seem prohibitive. Results suggest MSW paths featuring open windrow composting, mechanical-biological pre-treatment, material recovery facilities, and refuse-derived fuel production may be more appropriate to improve the sustainability of CDMX MSW management.

A data driven agent-based model that recommends non-pharmaceutical interventions to suppress Coronavirus disease 2019 resurgence in megacities.

Before herd immunity against Coronavirus disease 2019 (COVID-19) is achieved by mass vaccination, science-based guidelines for non-pharmaceutical interventions are urgently needed to reopen megacities. This study integrated massive mobile phone tracking records, census data and building characteristics into a spatially explicit agent-based model to simulate COVID-19 spread among 11.2 million individuals living in Shenzhen City, China. After validation by local epidemiological observations, the model was used to assess the probability of COVID-19 resurgence if sporadic cases occurred in a fully reopened city. Combined scenarios of three critical non-pharmaceutical interventions (contact tracing, mask wearing and prompt testing) were assessed at various levels of public compliance. Our results show a greater than 50% chance of disease resurgence if the city reopened without contact tracing. However, tracing household contacts, in combination with mandatory mask use and prompt testing, could suppress the probability of resurgence under 5% within four weeks. If household contact tracing could be expanded to work/class group members, the COVID resurgence could be avoided if 80% of the population wear facemasks and 40% comply with prompt testing. Our assessment, including modelling for different scenarios, helps public health practitioners tailor interventions within Shenzhen City and other world megacities under a variety of suppression timelines, risk tolerance, healthcare capacity and public compliance.

Cities as organisms: Urban metabolism of the four main Danish cities

Cities are responsible for the majority of global resource use and greenhouse gas emissions. Urban metabolism, which mimics metabolism of organisms as both require material and energy to function and further generate waste and emissions, is a useful framework to analyze levels of sustainability of a city through quantification of material and energy flows it uses and discards. The present study quantifies and compares the metabolic patterns of the four main Danish cities, Copenhagen, Aarhus, Odense, and Aalborg, from 2010 and 2015. We found their inflows of energy, water, and food and outflows of greenhouse gas emissions, wastewater, municipal solid waste, and construction and demolition waste have downsized over the six years. Our results affirm the impact of relevant policy and regulations in urban sustainability, with Danish cities showing more sustainable metabolic patterns than other world megacities previously reported in the literature. They also indicate that urban metabolic patterns can be highly dependent on the role and services that a city offers to its surrounding region (as a multicellular organism). Further strengthening of policies and regulations on “cities for sustainability” (i.e., focus on the sustainability of the entire multicellular organism) instead of a sole focus on “sustainable city” (i.e., each cell aiming at being sustainable independently from the others) would be important.

What can developing cities today learn from the urban past?

The downsides of density, including traffic congestion, contagious disease and crime, were common in Victorian London and classical Rome, just as they are today in Sao Paulo and Lagos. Our urban past provides lessons for developing world cities today. The first lesson, that I highlight, is that political power, not commerce, has long driven the growth of the world's largest cities, and that fact remains true for many developing world mega-cities today. The second lesson is that while market access fundamentally shaped the cities of the past, the power of transport to determine urban fortunes has declined. Transportation infrastructure no longer transforms cities unless it is accompanied by complementary investments, such as education. The third lesson is that infrastructure, such as sewers and roads, functions best when combined with incentives, which can ensure the adoption of sewers and discourage the abuse of highways. The fourth lesson is that the development of many western cities relied on a nexus of property rights for landowners, including the right to build, buy, alienate, mortgage and rent, that are far more limited in many developing world cities. The fifth lesson is that there is a menu of institutions for managing infrastructure, including direct public control, independent public authorities and public private partnerships. Local conditions, especially the level of public capacity, will determine the best choice among those institutions.

Monitoring Spatial-Temporal Transition Dynamics of Transport Infrastructure Space in Urban Growth Phenomena: A Case Study of Lagos—Nigeria

Lagos is one of the fastest growing world mega-cities with a huge urban mobility crisis, the traditional aggregate city’s development model could not provide reliable scientific solutions to monitor the competing demands of various land-use components and the urbanization’s effects on transport infrastructure space. This study uses a disaggregated predictive spatial modeling approach to investigate the evolutionary dynamics of transportation infrastructure space to address the fragmented urban chain process. The methodology involves analysis and modeling of the land-use spatial transition changes that have occurred over the past three decades using three Landsat imagery epochs (1984, 2013, and 2019) in remote sensing ARC-GIS 10.7. Furthermore, the prediction of the two-temporal milestones (2030 and 2050) using hybrid cellular automata-Markov (CA-Markov) implemented in IDIRISI SELVA 17.0 software when the tides of social-demographic factors were expected to bring about significant urban spatial transformation. The forecast results are expected to increase the area for transport infrastructure spaces by 93 km2 (7.3%) in 2030 and 157 km2 (12.4%) in 2050. The model’s kappa reliability coefficient estimates for the three temporal scales (k1984 = 85%; k2013 = 88% and k2019 = 89%) are higher than the 80% minimum adjudged strong agreement between the ground truth and prediction classified images in literature. The model provides efficient tool in urban development planning and sustainable transport decisions.

Unraveling the hidden organisation of urban systems and their mobility flows

Increasing evidence suggests that cities are complex systems, with structural and dynamical features responsible for a broad spectrum of emerging phenomena. Here we use a unique data set of human flows and couple it with information on the underlying street network to study, simultaneously, the structural and functional organisation of 10 world megacities. We quantify the efficiency of flow exchange between areas of a city in terms of integration and segregation using well defined measures. Results reveal unexpected complex patterns that shed new light on urban organisation. Large cities tend to be more segregated and less integrated, while their overall topological organisation resembles that of small world networks. At the same time, the heterogeneity of flows distribution might act as a catalyst for further integrating a city. Our analysis unravels how human behaviour influences, and is influenced by, the urban environment, suggesting quantitative indicators to control integration and segregation of human flows that can be used, among others, for restriction policies to adopt during emergencies and, as an interesting byproduct, allows us to characterise functional (dis)similarities of different metropolitan areas, countries, and cultures.

Inequalities in avoidable hospitalisation in large urban areas: retrospective observational study in the metropolitan area of Milan

ObjectiveSignificant inequalities in access to healthcare system exist between residents of world megacities, even if they have different healthcare systems. The aim of this study was to estimate avoidable hospitalisations...

Effects of Different Urbanization Levels on Land Surface Temperature Change: Taking Tokyo and Shanghai for Example

The influence of different urbanization levels on land surface temperature (LST) has attracted extensive attention. Though both are world megacities, Shanghai and Tokyo have gone through different urbanization processes that urban sprawl characterized by impervious surfaces was more notable in Shanghai than in Tokyo over the past years. Here, annual and seasonal mean LST in daytime (LSTday), in nighttime (LSTnight), and LSTdiff (annual and seasonal mean difference of LST in daytime and nighttime) were extracted from the MODIS LST product, MYD11A2 006, for 9 typical sites in Shanghai and Tokyo from 2003 to 2018, respectively. Then the effects of the urbanization levels were analyzed through Mann-Kendall statistics and Sen’s slope estimator. The trends of change in LSTday and LSTdiff for most sites in Shanghai, an urbanizing region, rose. In addition, there was no obvious regularity when considering seasonal factors, which could be due to the increasing fragmentized landscapes and scattered water bodies produced by urbanization. By comparison, the change in LST in Tokyo, a post-urbanizing region, was regular, especially in the spring. In other seasons, there was no obvious trend in temperature change regardless of whether the land cover was impervious surface or mountain forest. On the whole, vegetation cover and water bodies can mitigate the urban heat island (UHI) effect in urban regions. For more scientific urban planning, further analysis about the effect of urbanization on LST should focus on the compound stress from climate change and urbanization.

Characterization and comparison of groundwater quality and redox conditions in the Arakawa Lowland and Musashino Upland, southern Kanto Plain of the Tokyo Metropolitan area, Japan

Groundwater is essential for the Earth biosphere but is often contaminated by harmful chemical compounds due to both anthropogenic and natural causes. A key factor controlling the fate of harmful chemicals in groundwater is the reduction/oxidation (redox) conditions. The formation factors for the groundwater redox conditions are insufficiently understood. In this study, long-term groundwater quality beneath one of the world megacities was monitored and evaluated. We measured and compared hydrogeochemical conditions including groundwater quality (35 chemical parameters) and redox conditions of five aquifers in the Arakawa Lowland and Musashino Upland, southern Kanto Plain of the Tokyo Metropolitan area, Japan. Monitoring results suggested the following: The main origin of groundwater is precipitation in both the Lowland and Upland areas. The three aquifers in the Arakawa Lowland are likely fully separated, with one unconfined and two confined aquifers under iron reducing and methanogenic conditions, respectively. Oppositely, in the Musashino Upland, the water masses in the two aquifers are likely partly connected, under aerobic conditions, and undergoing the same groundwater recharge and flow processes under similar hydrogeological conditions. The different groundwater redox conditions observed are likely caused by the very different groundwater residence times for the Arakawa Lowland and Musashino Upland.

International Practice of Logistical Decisions of Metropolis’ Parking Spaces: Comparative Analysis

Analysis of foreign and Russian experience in logistics solutions in the organization of parking space for personal transport in the world's megacities was carried out by a search study. The method of content analysis of information was used as the main method. Two main approaches to content analysis were applied: formalization, i. e. the presence of unambiguous rules to identify the desired characteristics of content and statistical significance, i. e. the elements of interest should meet with sufficient frequency for the study. Since 2007, the population of large cities has been steadily growing. Worldstats predicts that by 2030, the population of the 25 fastest growing urban agglomerations will increase by another 113 million people. The main challenge for the development of large cities is how to place the increasing population within the limited boundaries of megacities, including how to organize residential and public spaces, including parking spaces, in limited areas.

Dynamics of various population groups in a two-dimensional spatial economy model.

The system of parabolic partial differential equations, which describes the dynamics of various population groups in an urban environment, is considered. The model takes into account both the interaction between different groups in the process of their cohabitation and the diffusion processes of population migration. Various examples of world megacities are considered and some general principles of urban development are formulated.

Expediency of modification of city transport system by implementation of passenger water transport

The object of research is the integration of local passenger water transport in the transport system of the city. Among a number of problematic issues, one can single out the unpreparedness of the urban transport infrastructure for the implementation of water transport for the transport of passengers, although this type of transport is an important component of intercity and suburban passenger transport in world megacities located on water arteries.Water transport is characterized and passenger water transport in Ukraine is analyzed. The definition of «transport system» as a whole and separately in part of urban passenger traffic is investigated. The components of the transport system of the city are determined.The structure of the city transport system in Kyiv (Ukraine) is investigated and supplemented with its new subsystem in the element «city passenger transport» – local passenger water transport. Such a structural change makes it possible to qualitatively improve the existing transport supply of cities with water areas, and to offer local residents an alternative mode of transport. Implementation of a new type of urban passenger transport in the transport system of the city requires its detailed study. Therefore, this type of transport is structured, its classification is provided, the concept of «local passenger water transport» and its types are formulated: Water Bus and Water Taxi, which allows to offer them for further use in the scientific environment, in relation to local passenger water transport.As part of the research, it is proposed to identify elements of local passenger water transport, namely: passengers, transport, local passenger transport enterprises, regulatory entities, and local authorities. Each of the elements is proposed to be structured by type.Thanks to this, a modified scheme of the system of urban passenger transport is developed, which provides the basis for the harmonious implementation of this type of transport. The implementation of the proposed changes is justified by the socio-economic significance of this type of transport and the necessary qualitative structural changes in the urban transport system.