Urban Hazardsand Mega-Cities  David Alexander  University College London
In 2006 the worlds population       became 50% urban. By 2050   less than 30% will be rural dwellers.The rich countries ar...
What does urban mean?• There is no general definition  or population threshold.• It implies a certain concentration  of po...
The world’s population is urbanizing much faster than it is growing.By 2025 four billion peoplewill be urban dwellers.Ther...
Rate of urbanisation in developingcountries is 4%, and 3-5% per yearis the rate of growth of megacitiessuch as:-• Dhaka, B...
Megacities may be:- • megalopolitan areas (megalopolis) • international urban corridors and axes • polycentric agglomerati...
City          Country     Population   Growth rate   Tokyo          Japan       34.2 mn         0.6% Guangzhou         Chi...
Large cities constitute the greatestconcentrations of natural hazard risk   and are poles of attraction for    other kinds...
In places like Port au Prince, Haiti, and Luanda, Angola, the statusquo ante has often seemed as bad      as any disaster ...
The "informal housing"of the poor is usually  relegated to the  least safe places
Post-disaster urban reconstruction• damaged assets can seldom be  rebuilt to the original standards• reconstruction must t...
Increasing reliance of urban hazard managers on technological systemsin order to reduce risk - a general   characteristic ...
Relatively minor damage to transportation    systems can paralyse a megacity
İstanbul
Tokyo
Tehran
Kathmandu
Hong Kong
Barcelona
Post-earthquake urban fire in Kobe, 1995
Calcutta
Perils of the urban-rural interface
Challenges to DRR posed by megacities:-• scale and geographical complexity• environmental impact  and resource consumption...
Conclusions• Well-established parts of cities  may slowly have developed  resilience against hazards.• Urban sprawl may ta...
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Urban Hazards and Megacities

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Urban Hazards and Megacities

  1. 1. Urban Hazardsand Mega-Cities David Alexander University College London
  2. 2. In 2006 the worlds population became 50% urban. By 2050 less than 30% will be rural dwellers.The rich countries are already >75% urban.
  3. 3. What does urban mean?• There is no general definition or population threshold.• It implies a certain concentration of population and services.• megacity: an urban agglomeration with a population of more than 10 million.
  4. 4. The world’s population is urbanizing much faster than it is growing.By 2025 four billion peoplewill be urban dwellers.There are 26 megacities(first five in Asia)Another ten cities have populationsof more than 5 million inhabitants.
  5. 5. Rate of urbanisation in developingcountries is 4%, and 3-5% per yearis the rate of growth of megacitiessuch as:-• Dhaka, Bangladesh• Delhi, India• Guangzhou, China• Karachi, Pakistan• Lagos, Nigeria
  6. 6. Megacities may be:- • megalopolitan areas (megalopolis) • international urban corridors and axes • polycentric agglomerations of connected towns and citiesDynamic forces:-• urban sprawl and suburbanisation• distinction between poor and rich areas and marginalisation of the poor• counter-urbanisation into smaller centres.
  7. 7. City Country Population Growth rate Tokyo Japan 34.2 mn 0.6% Guangzhou China 24.9 4.0 Seoul South Korea 24.5 1.4 Delhi India 23.9 4.6 Mumbai India 23.3 2.9 Mexico City Mexico 22.8 2.0New York City USA 22.2 0.3 São Paulo Brazil 20.8 1.4 Manila Philippines 20.1 2.5 Shanghai China 18.8 2.2
  8. 8. Large cities constitute the greatestconcentrations of natural hazard risk and are poles of attraction for other kinds of disaster risk. Urbanization, perhaps even metropolitanization, is one of the principal factors that is propellingthe world-wide rise in disaster losses.
  9. 9. In places like Port au Prince, Haiti, and Luanda, Angola, the statusquo ante has often seemed as bad as any disaster impact.
  10. 10. The "informal housing"of the poor is usually relegated to the least safe places
  11. 11. Post-disaster urban reconstruction• damaged assets can seldom be rebuilt to the original standards• reconstruction must take account of new norms and requirements• reconstruction requires more space.
  12. 12. Increasing reliance of urban hazard managers on technological systemsin order to reduce risk - a general characteristic of municipal and regional hazard management.
  13. 13. Relatively minor damage to transportation systems can paralyse a megacity
  14. 14. İstanbul
  15. 15. Tokyo
  16. 16. Tehran
  17. 17. Kathmandu
  18. 18. Hong Kong
  19. 19. Barcelona
  20. 20. Post-earthquake urban fire in Kobe, 1995
  21. 21. Calcutta
  22. 22. Perils of the urban-rural interface
  23. 23. Challenges to DRR posed by megacities:-• scale and geographical complexity• environmental impact and resource consumption• hazardous locations (especially coastal)• sensitive to climate change effects• many megacities are home to the vast slums of the poor and marginalised.
  24. 24. Conclusions• Well-established parts of cities may slowly have developed resilience against hazards.• Urban sprawl may take cities into unstabilised hazard zones.• Environmental discrimination relagates the poor and marginalised to the least safe urban environments.• megacities are vast urban systems with equally huge vulnerabilities.• Sustainability is a general issue for them.

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