Future Cities and Environmental Sustainability: A Comprehensive Review

Historical Perspectives and the Evolution of Cities

• Historical Significance: Cities have historically served as the centers of human development and technological advancement. While some ancient cities have survived and flourished for millennia, others have collapsed, providing critical lessons for future urban planning.
• Ancient Exemplars and Lessons:
  • Angkor Wat (Khmer Civilisation, Cambodia): Ancient engineers developed a sophisticated system of canals for water control and distribution. This system irrigated agriculture within city bounds to supply citizens with food and managed environmental extremes by preventing flooding from Monsoon rains and storing water for droughts. Despite this, the city collapsed in $1431$; climate change resulting in extended droughts is cited as a factor that Khmer engineering could not overcome.
  • Tenochtitlán (Aztec Capital, Mexico): Built in a lake bordered by swamps, engineers controlled water flow to create "floating gardens" (agricultural irrigation) and used causeways and canals for connection. They separated brackish lake water from spring water to provide drinking water. At the time of the Spanish conquest in $1519$, it had a population of $200,000$ to $300,000$. It evolved into modern-day Mexico City, which now has a population of $21 \times 10^6$.
• Philosophical Approach: The review cites George Santayana: ‘‘Those who do not remember the past are condemned to repeat it.’’ Future city design necessitates learning from historical failures and successes while applying current advanced technologies.

Strategic Principles for Sustainable Urban Design

• Citizen-Centric Focus: Future cities must prioritize serving inhabitants by providing increased prosperity and desirable lifestyles without negatively impacting other regions (e.g., exporting carbon emissions through imports manufactured by fossil fuels).
• Resource Management Balance: The energy and material content of imported goods must be balanced by those of exports. Key operational components include:
  • Wide-scale utilization of renewable energy.
  • Waste management and minimization.
  • Water harvesting and recycling.
  • Enhancement of landscape and biodiversity.
  • Green transport systems.
  • Innovative construction methods using low/zero-carbon buildings.
  • Local food production.
• Adaptive Systems: Buildings should transition from passive entities to active, adaptive spaces that leverage the environment for heating, cooling, light, and electricity. Integrated smart management control systems using wireless sensor networks are essential for monitoring and sustainability.
• Planning Flexibility: Strategic approaches should avoid overly centralized or rigid parameters to allow for local architectural expression and community-based designs.

Global Urbanization Challenges and Mitigation Strategies

• Urbanization Projections: The United Nations estimates that the urban populations of Africa, Asia, and Latin America will double between $2000$ and $2030$ (from $1.9 \times 10^9$ to $3.9 \times 10^9$). By $2030$, over $60 \%$ of the world’s population will reside in cities. By $2050$, the urban population is estimated to reach $6.4 \times 10^9$.
• Impacts and Specific Mitigation Strategies:
  • High Traffic Density: Mitigated by efficient public transport and compact city design.
  • High Waste Volume: Mitigated by recycling (note: $75 \%$ of solid waste is recyclable, though $70 \%$ is currently discarded).
  • Urban Warming: Mitigated by increasing green space and using reflective materials.
  • Air Pollution: Mitigated by $CO_2$ capture, filtering exhaust gases, and increasing industrial efficiency.
  • Energy Resource Depletion: Mitigated by renewable sources and low-energy building design.
  • Biodiversity Loss: Mitigated by developing protection areas and green spaces.
  • Water Scarcity: Mitigated by purification, desalination, and rainwater harvesting.
  • Food Demand/Poverty: Mitigated by vertical farming, artificial food production, and "greening the deserts."
  • Land Shortage: Mitigated by multi-functional buildings and creative architectural designs.
  • Social Cohesion: Mitigated by improving the socio-cultural environment and communal events.
• Land Conversion Examples:
  • Concepción, Chile: Between $1975$ and $2000$, $1734$ hectares of wetlands and $1417$ hectares of agricultural/forest land were converted to residential use.
  • Accra, Ghana: An estimated $2600$ hectares of agricultural land are converted annually.

Urban Productivity and Economic Sustainability

• Productivity Metrics: Urban productivity is defined by how efficiently a city transforms inputs into outputs, with Gross Domestic Product ($GDP$) per capita serving as a common proxy. Population serves as a proxy for human capital inputs.
• National Comparisons (2008 data): While $22$ of the top $30$ largest urban areas were in emerging economies, only $7$ ranked in the top $30$ by total urban $GDP$: Mexico City, Sao Paulo, Buenos Aires, Moscow, Shanghai, Mumbai, and Rio de Janeiro. No African or Middle Eastern cities were in the top $30$.
• Emission Projections (Singh and Kennedy Study):
  • A projection tool for $3646$ urban areas suggests that for high-growth scenarios, $CO_2$ emissions from electricity usage will double by $2020$ and more than quadruple by $2050$.
  • Urban densification significantly increases transportation-sourced emissions and energy consumption, while the heating sector is less affected by density changes.

Future City Planning Models and Movements

• Historical Planning Failures:
  • 19th-Century Britain: Uncontrolled growth led to the "horrendous" conditions described by Charles Dickens and Henry Mayhew, characterized by lack of sanitation, disease, and child labor.
  • Mid-20th Century "Concrete Visions": Inspired by Le Corbusier, high-rise tower blocks and "streets in the sky" in post-WWII Britain failed socially (isolation and crime) and technically (poor quality), leading to large-scale demolitions in the $21\text{st}$ century.
• Modern Strategic Movements:
  • Garden City Movement: Originating with Ebenezer Howard (Letchworth and Welwyn Garden City), it emphasized integrated transport and green belts. Modern adaptations (announced by the UK government) focus on community ownership, mixed-tenure affordable housing, and allotments for food growth.
  • Prince Charles and Poundbury: Advocates for local vernacular architecture and a return to traditional community layouts to avoid the insensitivity of modernism.
  • Grassroots Initiatives: Inclusion of farmers' markets, community-supported agriculture, and carpooling.
• Talent Retention: Chongqing, China, has a training program to transition rural migrants from manual to skilled work ($1/3$ of migrants benefited by $2009$). Dubai promotes engineering and IT education to retain qualified individuals.

International Case Studies of Sustainable Urban Projects

• Zero Carbon Building (ZCB), Hong Kong: A $14,700 \, m^2$ project featuring a 3-storey building and landscape area at the heart of Kowloon Bay. It uses integrated design seeing the building and woodland as a single entity.
• Jockey Club Innovation Tower, Hong Kong: A 15-storey structure designed by Zaha Hadid, using a unique geometry to minimize land footprint while maximizing multi-functional space.
• Sweden:
  • Malmo: Features passive houses utilizing wind, geothermal, and solar energy, with specific attention to rainwater and sewage treatment.
  • Hammarby Sjostad (Stockholm): Built on an industrial/harbor area for $25,000$ inhabitants ($200$ ha). Energy demand is limited to $60 \, kWh/m^2$ per year, with electrical energy capped at $20 \, kWh/m^2$ per year.
• London:
  • Beddington Zero Energy Development (BedZED): Completed in $2002$, it includes $82$ affordable dwellings on $2500 \, m^2$, combining workspace and housing to achieve zero carbon standards.
• Japan:
  • Kitakyushu Eco-Town: Built to reverse the industrial contamination of the $1960\text{s}$. It focuses on local recycling of items from bottles to bicycles and requires commercial facilities to be transparent to citizens to reduce distrust.
• Middle East Mega-Projects:
  • Masdar City, Abu Dhabi: Designed as the first low-carbon, zero-waste sustainable city powered by renewables for $40,000$ residents.
  • Silk City, Kuwait: Scheduled for completion in $2023$, a $132 \times 10^9 \, USD$ project for $750,000$ residents featuring the Burj Mubarak al-Kabir tower.
  • King Abdullah Economic City, Saudi Arabia: Covers $173 \, km^2$, aiming to create $1 \times 10^6$ jobs for a population where $40 \%$ are under $15$ years old.
• Khazar Islands, Azerbaijan: A $100 \times 10^9 \, USD$ sustainable city for $1 \times 10^6$ inhabitants, including the $2 \times 10^9 \, USD$ Azerbaijan Tower, designed to withstand magnitude $9.0$ earthquakes.

Futuristic and Extremophile Urban Concepts

• Underground Cities: Proposed for cities like London with high real estate costs. Concept includes putting major roads into tunnels to leave surfaces for parks.
• Ocean Spirals (Shimizu Corporation, Japan): Self-sufficient underwater cities with $5,000$ inhabitants housed in $500 \, m$ diameter spheres. Connected to the ocean floor ($4000 \, m$ deep) for resources, aquaculture, and desalination. Estimated cost: $16 \times 10^9 \, GBP$.
• Lilypad (Vincent Callebaut): Floating cities for $50,000$ people that follow ocean currents, avoiding the risk of sea-level rise.
• The Venus Project (Jacque Fresco): A circular city model using cybernetic systems to maintain automated functions. It proposes a moneyless, technological civilization to eliminate inequality and greed.
• City in the Sky (Tsvetan Toshkov): An imaginary tranquil oasis shaped like a lotus flower, positioned above polluted mega-cities.
• Endless (Vertical) City: A 55-storey tower for London with ramps acting as "vertical streets" to save horizontal space.

Disaster Reconstruction and Rapid Sustainably-Built Projects

• Wenchuan and Qingchuan (Sichuan, China): Following the $2008$ earthquake, a research team led by Prof. Zhu Jingxiang (CUHK) developed an integrated light-structure system.
• New Bud Primary School: Built in only two weeks at Xiasi village. The school is low-cost, durable, has high thermal performance, and high energy-saving capacity.

Innovative Materials and Construction Technologies

• 3D Printing and Robotics: Use of robotic arms with three-axis movement to construct prefabricated modules. This minimizes defects and waste. In China, 3D printing has been used to create five-storey homes from construction waste at a cost of roughly $100,000 \, GBP$.
• Timber/Wood Construction:
  • Carbon Sequestration: Each $1 \, m^3$ of wood stores approximately $0.5$ to $0.9$ tonnes of $CO_2$. Specifically, $1 \, kg$ of wood can store $9 \, kg$ of $CO_2$.
  • Tall Wood Buildings: Michael Green designed a 30-storey tower for Vancouver, Canada, to overtake the Forte Building (Melbourne) and Stadthaus (London) as the tallest wooden construction.
  • Comparison of CO2 Release per kg Material:
    • Wood: Negative balance.
    • Steel: $2 \, kg \, CO_2/kg$.
    • Concrete: $0.2 \, kg \, CO_2/kg$.
    • Aluminum: $27 \, kg \, CO_2/kg$.
• Nanotechnology: Applying nano-scale coatings of titanium dioxide provides a self-cleaning effect for windows and roof tiles by breaking down dirt.
• Regulations: The EU’s Energy Performance of Buildings Directive (EPBD) requires all new buildings to be "nearly zero energy buildings" (nZEB) by the end of $2020$.

Urban Agriculture and Food Security Strategies

• The Space Constraint: Currently, feeding the global population requires agricultural land equal to half of South America. By $2050$, $50 \%$ more food production will be required.
• Historical/Crisis Precedents: Britain and Germany used spare ground during WWI/WWII. Cuba turned to intensive urban agriculture following the collapse of the Soviet Union in $1990$.
• Vertical Farming: Skyscrapers for food production.
  • One dedicated vertical farm could feed up to $50,000$ people.
  • Energy Balance (Al-Chalabi Study): A study found that vertical farms with floor areas less than $500 \, m^2$ can be self-sufficient using roof/facade PV panels. For areas exceeding $500 \, m^2$, the space for PV is insufficient (as shown in Table 2):
    • $100 \, m^2$ floor area: Total Energy Demand $148 \, kWh$; PV Capacity $593$ panels; Feasible.
    • $625 \, m^2$ floor area: Total Energy Demand $138,311 \, kWh$; PV Capacity $1,675$ panels available vs. $3,294$ required; Not Feasible.
• Current Vertical Farm Projects:
  • Michigan, USA: The world's largest vertical farm opened in $2014$ with $17 \times 10^6$ plants using LED light.
  • Sky Greens (Singapore): A four-storey building using conveyor belts to rotate soil-based plants for sunlight exposure, increasing food production by a factor of $10$ compared to traditional farming.
  • Avesta Concern (Azerbaijan): Khazar Islands projects.

The Waste-to-Food Eco-Cycle

• Recycling Human Waste: Historically used as fertilizer but discouraged in developed nations due to pathogens and heavy metals.
• Pearl Process (Ostara): A technology that recovers phosphorus, nitrogen, and magnesium from wastewater to produce a slow-release fertilizer called Crystal Green, which has low heavy metal content. The first European plant was installed in Slough, UK.

Next-Generation Transport Systems

• Individual Air/Land Travel: The Aero-Mobil is a flying car that fits in standard parking spaces, uses regular gasoline, and has been in flight testing since October $2014$. It includes autopilot and an advanced parachute deployment system.
• Long-Distance High-Speed Travel:
  • Maglev Trains: Exploit superconductivity for extreme speeds.
  • Aero-train: Part train, part aircraft; it flies on an air cushion along a concrete track using wing and ground effects to minimize drag.
  • Evacuated Tube Transport (ETT): A concept proposing vehicles in a vacuum to eliminate air resistance. Research into superconducting maglev trains in ETT suggests speeds up to $6,500 \, km/h$ ($4,039 \, mph$), enabling travel from New York to Beijing in two hours.
• Autonomous Systems: Chinese engineers tested a Hongqi Q3 car traveling $286 \, km$ guided by sensors and cameras without GPS. These cars could be networked to predict traffic jams using satellite systems.

Technical and Social Management of the Urban Environment

• Urban Heat Island Effect (UHIE):
  • Refers to urban temperatures being higher than the surrounding countryside, with a typical difference of $3 \, K$.
  • Caused by solar heat absorption by roads/buildings, vehicle heat, and air conditioner exhaust.
  • Impact on Health: Heatwaves lasting over $5$ days lead to excess mortality, especially in the young and elderly. Nighttime temperature excess correlates more strongly with death rates than daytime temperature.
• Mitigation Framework:
  • Albedo: Using reflective materials and "cool buildings."
  • Green Infrastructure (GI): Increasing urban parks and green roofs. A study in Greater Manchester, UK, showed that increasing GI by $10 \%$ could reduce temperatures by up to $2.5 \, ^\circ C$ under high-emission scenarios (Gill et al. study).
  • Ventilation: Designing street orientation and green corridors to encourage airflow.
• Smart Infrastructure Monitoring:
  • Songdo, South Korea: Monitors traffic, waste, and energy usage.
  • Rio de Janeiro: High-tech centers for public safety and disaster response.

Socio-Economic Prosperity and Equitable City Governance

• The Wheel of Prosperity: A 5-dimension model to achieve urban well-being:
  1. Productivity: Contributing to economic growth and employment.
  2. Infrastructure: Deployment of water, sanitation, power, and ICT.
  3. Quality of Life: Social services, education, health, and safety.
  4. Equity and Social Inclusion: Minimizing poverty and income gaps.
  5. Environmental Sustainability: Protecting natural assets.
• Economic Inequality Statistics: Income gaps are expanding. In OECD countries, the richest $10 \%$ earn $9 \times$ more than the poorest $10 \%$. In Italy, Korea, and the UK, this multiple is $10 \times$. In Israel, Turkey, and the US, it is as high as $14 \times$.
• Governance Innovation: Using the "block-chain" algorithm (e.g., Ethereum platform) for city administration to increase transparency and minimize corruption. Distributed apps like "BoardRoom" are being explored for collaborative decision-making.
• Human Capital: Prosperity is not just material; cities must satisfy basic needs while allowing immaterial aspirations, contentment, and happiness to flourish.