Urban Hazards and Mega-Cities

David Alexander University College London

In 2006 the world's population became 50% urban. By 2050

less than 30% will be rural dwellers. The rich countries are already >75% urban.

What does 'urban' mean?

• There is no general definition or population threshold.

• megacity: an urban agglomeration with a population of more than 10 million.

• It implies a certain concentration of population and services.

The world’s population is urbanizing much faster than it is growing.

There are 26 megacities (first five in Asia)

Another ten cities have populations of more than 5 million inhabitants.

By 2025 four billion people will be urban dwellers.

Rate of urbanisation in developing countries is 4%, and 3-5% per year is the rate of growth of megacities such as:- • Dhaka, Bangladesh • Delhi, India • Guangzhou, China • Karachi, Pakistan • Lagos, Nigeria

Megacities may be:- • megalopolitan areas (megalopolis) • international urban corridors and axes • polycentric agglomerations of connected towns and cities

Dynamic forces:- • urban sprawl and suburbanisation • distinction between poor and rich areas and marginalisation of the poor • counter-urbanisation into smaller centres.

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 2.0

New 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

Large cities constitute the greatest concentrations 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 propelling

the world-wide rise in disaster losses.

In places like Port au Prince, Haiti, and Luanda, Angola, the status

quo ante has often seemed as bad as any disaster impact.

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 take account of new norms and requirements

• reconstruction requires more space.

Increasing reliance of urban hazard managers on technological systems in order to reduce risk - a general

characteristic of municipal and regional hazard management.

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

• 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.

Challenges to DRR posed by megacities:-

• 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.

Conclusions