In 1991, the city of Medellín in Colombia registered a homicide rate of 381 per 100,000—among the highest ever recorded anywhere. In neighboring cities like Barranquilla, Bogotá, and Cali, the levels of violence associated with drug trafficking and political unrest were equally fearsome. Entire neighborhoods were cordoned-off, even to police and public service providers. Gangs, paramilitaries, and guerrillas routinely brought city services to a standstill. The rampant insecurity had severe economic consequences, shaving off anywhere between 4 and 11 percent of the country’s gross domestic product a year.

Today, however, levels of violent crime in Colombia’s cities have plummeted to levels not seen since the 1970s. Medellín’s current homicide rate is around 21 per 100,000, far below that of Detroit, Baltimore, or New Orleans. Bogotá’s murder rate dropped from 80 per 100,000 in 1993 to just 16 today. Even Cali and Barranquilla’s stubbornly high murder rates fell to historic lows. This is good news, since these four cities account for roughly one third of all murders in the country. The national homicide rate is currently 22 per 100,000, the lowest since 1974.

While still facing sharp political polarization and difficulties implementing a hard-won peace deal, Colombia is today one of the region’s best economic performers, thanks largely to improvements in its cities. Bogotá, the capital, was rated by FDI Intelligence as one of Latin America’s top destinations for foreign direct investment and a City of the Future. Medellín was the winner of the World City Prize in 2016 and the World’s Most Innovative City in 2013, beating out New York City and Tel Aviv.

The transition of Colombia’s cities from fragility to resilience is breathtaking. It also shows how the pulse of cities offers insight into the health of nations. Fragile cities are a risk not just to their residents, but also to entire countries and regions—especially in those parts of the world where urbanization is proceeding at breakneck speed, as in Africa and Asia. Most cities in poorer countries are urbanizing before they industrialize, which can quickly overwhelm their abilities to deliver services. Referring to a roughly $75 trillion dollar infrastructure gap, the Bank of America Merrill Lynch estimated in 2017 that 80 percent of the world’s cities were fragile.

Yet measuring just how fragile a city is can be tricky business. That is because fragility cannot be readily boiled down to a single risk factor, such as homicide, lack of potable water, or pollution. Rather, fragility is the manifestation of a convergence of multiple stresses. As these risks accumulate, they undermine a city’s social contract and in extreme cases can push it to the brink of collapse. All cities are fragile to a greater or lesser degree—it is not the preserve of poorer urban agglomerations alone. Nor is fragility a permanent condition, as the case of Colombia’s remarkable rebound shows.

In order to empirically measure urban fragility, I broadened the lens to eleven risk factors, including the speed of population growth, levels of unemployment, income inequality, access to basic services (electricity), homicide rates, terrorism, conflict events, and exposure to natural hazards (including cyclones, droughts, and floods). My research extends to over 2,100 cities with populations of at least 250,000 inhabitants over a 15-year period.

One of the dominant drivers of fragility appears to be rapid unregulated urbanization. When cities grow fast—over 3 percent a year—city fragility is more likely. This is because cities experiencing sprawling slums, such as Karachi and Kinshasa, are also more predisposed to physical dispersion and social disorganization. Those are in turn correlated with crime and violence. By contrast, cities registering lower population growth rates tend to be more stable. In some Colombian cities, an increase of 1 percent in the population growth rate is associated with a 1.5 percent increase in crime victimization.

The most fragile cities (in red) are clustered in Africa, the Middle East, and Asia. (Map from  

Other drivers of urban fragility related to concentrated disadvantage, include inequality, unemployment, and poverty. From Baltimore to Lagos, criminal violence tends to be more prolific in unequal cities compared to those with a more equal distribution of income and basic services. Real and relative deprivation of income, property, service provision and social status are all connected to reduced social capital and social efficacy. The clustering and concentration of poverty—in some U.S. city neighborhoods the number of residents living below the poverty line exceeds 40 percent of the population—is associated with underperforming schools, poor housing and health conditions, and higher rates of incarceration and criminality.

Deficits in law enforcement and criminal justice can also aggravate city fragility. When residents lose confidence in their police officers, prosecutors, and judges, they are more inclined to turn to private—and in some cases vigilante—solutions. Where the reach of law enforcement is limited, or when policing is repressive, there also tends to higher levels of mistrust between neighbors. In cities as diverse as Dili and Detroit, the perception of insecurity has real effects, including decisions about whether to stay or migrate. Weak and uneven public security provision also has negative knock-on effects, including on the delivery of utilities, the cleaning of streets, and basic hygiene and sanitation.

Cities also succumb to fragility when facing weather-related shocks and natural disasters. Because of climate change, storm surges, catastrophic flooding, droughts and other extreme weather events are increasing in scale and intensity, affecting city residents and infrastructure. The extent of these risks is chilling: A review of over 1,300 cities determined that 56 percent of them are exposed to severe environmental disasters. This is all the more worrying considering that over two-thirds of the world’s cities are coastal and 1.5 billion people live in low-lying coastal areas.

When all these factors are combined and compared, global patterns are easier to detect. For example, 14 percent of the world’s cities with populations of 250,000 residents or more fall into the “very fragile” category, 66 percent can be classified as having “medium fragility,” and 16 percent register “low fragility” scores. Not surprisingly, rapidly urbanizing African and Asian cities are the most fragile: Roughly 92 percent of all African cities are either very or medium fragile, as compared to 85 percent in the case of Asian cities.

And where are the world´s most fragile cities? It turns out that the top three are all located in the same country: Mogadishu, Kismaayo, and Merca in Somalia. They’re followed by Kabul (Afganistan), Mosul (Iraq), Aden (Yemen), Kirkuk (Iraq), Juba (South Sudan), Ibb (Yemen), and Kunduz (Iraq). A rash of war-ravaged Syrian cities also fill out the top of the list.

Meanwhile, the least fragile cities are largely concentrated in Canada, Japan, Australia, the United States, and Norway. For example, Sarasota, Syracuse, and Ann Arbor in the U.S. figure at the top of the list, followed by Bournemouth (UK), Sakai (Japan), Canberra (Australia), and Oslo (Norway). Virtually all of Colombia´s 25 largest cities currently fall in the medium category, though most will soon register dramatic improvements owing to the peace agreement signed last year.

The World’s Most Fragile Cities (2015)

Ranking City name Country Fragility score
1 Mogadishu Somalia 3.7
2 Kismaayo Somalia 3.7
3 Kunduz Afghanistan 3.67
4 Merca Somalia 3.6
5 Ibb Yemen 3.6
6 Ta'Izz Yemen 3.6
7 Kabul Afghanistan 3.58
8 Aden Yemen 3.5
9 Al-Mukalla Yemen 3.5
10 Sana'A Yemen 3.45
11 Al-Mawsil (Mosul) Iraq 3.36
12 Goma Democratic Republic of the Congo 3.33
13 Bunia Democratic Republic of the Congo 3.3
14 Baaqoobah Iraq 3.3
15 Faloojah Iraq 3.3
16 Hillah Iraq 3.3
17 Ramadi Iraq 3.3
18 Al-Hasakeh Syrian Arab Republic 3.3
19 Al-Raqqah Syrian Arab Republic 3.3
20 Al-Basrah (Basra) Iraq 3.27
21 Kandahar Afghanistan 3.25
22 Balkh Afghanistan 3.25
23 Al-Hudaydah Yemen 3.22
24 Bujumbura Burundi 3.2
25 Bukavu Democratic Republic of the Congo 3.2


The good news is that decision makers are waking up to the risks of city fragility. And not a moment too soon: A broad understanding of urban risk is critical to developing appropriate solutions. There is growing investment not just in developing smarter cities, but also ones that are more resilient to multiple threats. As Colombia’s experience shows, this requires investing in comprehensive solutions that build the capacities of individuals, neighborhoods, businesses, and institutional systems to survive, adapt, and grow. It is not enough to simply prepare for future shocks. What is also needed are interventions focusing on areas suffering from social and economic inequality and poor service delivery that sap a city’s ability to respond to disasters.

One hopeful lesson from Colombia is that urban fragility can be designed-out. It requires establishing forward-looking city plans, agile decision-making structures, and solutions that are inter-systemic. In Medellín, that’s what city leaders did: Rather than focusing on a single risk—threats to law and order—successive mayors adopted inter-sector approaches, an approach known locally as “urban acupuncture.” Strategies involved highly targeted community policing, municipal infrastructure improvements, better public transportation, and integrated public spaces such as “library parks” that combined green areas, community centers, and learning facilities.

So what is the key takeaway? It takes many factors to render a city fragile, and overcoming fragility requires reimagining the urban landscape and accounting for all of those risks, not just a single one.