By Dr. Nat Cobb

I would like to explore the influence of health on the question: “will megacities be a crucible of disaster or innovation?” It goes without saying that an uncontrolled epidemic in a large city would be a disaster of potentially global impact. What are the factors that might contribute to the resilience or vulnerability of a city? Can we predict which are the most vulnerable?

Large cities have many positive qualities that contribute to their resilience and vitality, among them being the abundance of human resources, the efficiency of high population density, and the rapid exchange of ideas and innovation. A single well-placed hospital or clinic can serve many thousands of people. An emerging public health problem can be rapidly detected and mitigated. Centrally placed resources for disaster preparedness can be quickly available to a large population.  The highly networked nature of cities adds resilience through the capacity for rapid communication and emergency response.1

As a city expands to “megacity” status, however, a number of negative factors become more prominent. The basic sanitation infrastructure to provide potable water and waste removal may be severely challenged. Environmental degradation adversely affects health and quality of life. As crowding increases, the lack of mobility affects access to health care, and decreases independence.

Socially, rapid growth through in-migration leads to a lack of community cohesion, breakdown of social structures, inadequate education, and increased crime rates.2Physical inactivity and limited access to healthy foods contribute to a rise in chronic diseases, which disproportionately burden the health system and degrade productivity. A high level of disparities in wealth, education, and health can put further strain on social stability and resilience.

Cities under these sorts of stresses often balance in a dynamic equilibrium with just-in-time fixes. The equilibrium may become increasingly fragile through the cumulative “friction” of many negative forces, such as a gradual increase in chronic disease prevalence, malnutrition, and slow-burning epidemics like HIV. Like a lightning strike in a bone-dry forest, all it takes then is the sudden kick of a hurricane, a virulent infectious disease, or a war to tip the balance toward chaos and the loss of many lives.

Not every epidemic is a disaster. If the problem is rapidly recognized, adequate resources are brought to bear, and the population cooperates with control measures, then the disruption of even a deadly disease can be minimized. When and where do catastrophic epidemics occur? Can we build a model that will assign a probability to their occurrence? I suggest that a reasonably predictive model for megacities (>10 million) might be constructed with only two inputs: growth rate, and resources available. The rate of growth can be estimated by demographic surveys or census; resources might be measured as per capita public sector spending, or  perhaps per capita gross economic activity. As long as the city is able to feed, employ and clean up after its population, it will indeed be a crucible for innovation. When population growth overwhelms the ability of infrastructure to keep up, we will see an inflection point with rapidly increasing vulnerability to a catastrophic breakdown.

The model might be further improved by adding other variables: an index of socio-economic disparity; population density; air and water pollution; and a measure of the functionality of government. One might also include factors for “special case” vulnerabilities such as active faults or volcanoes, refugee situations, etc.

A predictive model would be valuable for institutions like the World Bank, World Health Organization, and the US Centers for Disease Control and Prevention, who could focus their surveillance efforts and interventions on the most likely flashpoints. If the models do indeed show a predictable inflection point, extra resources might be summoned to address the weakness in a city that was approaching that point. Our increasingly networked systems are ever more vulnerable to disruption from a distant disaster, so it matters to all of us that Lagos, Nigeria (11.2 million) has a growth rate of 4%, and that Karachi, Pakistan is at 13.9 m and 3.2%.3 Are they at higher risk than the Chinese mega-region of Hong Kong-Shenzhen-Guangzhou (120 m, 6-12%)?4 We need a model.

 

Citations

1.      The Age of the Unthinkable, Joshua Cooper Ramo. Little, Brown and Co. 2009.

2.      Instant City; Life and Death in Karachi. Steve Inskeep. The Penguin Press, 2011.

3.      World Urbanization Prospects, 2011 Revision. United Nations Department of Economic and Social Affairs/Population Division.

4.      State of the World’s Cities 2008/2009. United Nations Human Settlements Programme, Nairobi, Kenya.

 

Dr. Nat Cobb is an assistant professor in the Dept. of Family and Community Medicine, UNM School of Medicine, the former Chief, Chronic Disease Branch, Division of Epidemiology, Indian Health Service, and Capt. (ret.), U.S. Public Health Service.