Over the last ten years, the number of people living in megacities with over 10 million people has increased tenfold. According to the 2011 United Nations report on world population prospects, this trend will only increase, with one out of every five people on the planet projected to inhabit a megacity by 2025. As these megacities rapidly grow, more and more people will rely on urban resilience systems to protect them from natural and manmade disasters.
Here’s a look at how the five fastest growing megacities have started to prepare for disaster in the face of enormous population growth:
1. Lagos, Nigeria – Projected Annual Growth Rate 2011-2025: 3.71% 
As evidenced by the massive 2012 floods that killed and displaced hundreds of citizens around the city, water management is a major environmental problem for Lagos. To prevent further encroachment by the sea, the Nigeria government has built Eko Atlantic City, a 4-square mile extension of Lagos that juts into the Atlantic Ocean. Eko Atlantic City hopes to mitigate both the problem of flooding, with debatable protective barriers like a 35-foot tall seawall, and the problem of growth, by using the extension as a site for new apartments. However, considering that the recent floods occurred after most of the project had been completed, the ultimate effectiveness of the project remains to be seen.
2. Dhaka, Bangladesh – Projected Annual Growth Rate 2011-2025: 2.84%
Although natural disasters like earthquakes, cyclones, and floods frequently plague Dhaka’s citizens, one of the city’s biggest environmental challenges comes from the rapidly growing population itself. According to the World Bank , brick production accounts for 38% of all air pollution in Dhaka, and the problem will only get worse as the rising population necessitates more construction. However, newer kiln technologies promise to reduce the premature deaths caused by kiln emissions by 40-60%. The government has helped push for conversion loans that help brick makers pay for new kilns and changes in environmental policy that punish those who don’t. Unfortunately, mismanagement of those programs has resulted in only 17% of brick makers switching to cleaner kilns since the government push began in 2010.
3. Shenzhen, China – Projected Annual Growth Rate 2011-2025: 2.71%
Many Chinese cities became choked with automotive air pollution when the growing economy and the growing population combined to produce millions of new drivers. To reverse that trend, the Chinese government picked 13 cities to switch over to green vehicles, and Shenzhen has led the way with 1,000 electric buses and 500 electric taxis. Additionally, the city has launched a hefty subsidy on electric cars for its citizens and paid for new recharging stations. Even more ambitious, the city aims to convert all its buses and taxis to electric vehicles by 2016.
4. Karachi, Pakistan – Projected Annual Growth Rate 2011-2025: 2.68%
With a fraying social fabric and a corrupt government limiting the development of disaster prevention projects, Karachi has turned to human networks instead of infrastructure to provide resilient services to the city’s fast-growing and vulnerable slum population. The Orangi Pilot Project (OPP), a civic welfare group founded in 1989 to help the Orangi squatter neighborhood, initiated a number of programs to mitigate the effects of recent earthquakes and floods. After the last earthquake, the OPP helped rehabilitate the water supply and sanitation infrastructure, and after the 2011 flood, the OPP partnered with the government and other NGOs to set up handpumps for water and repair damaged houses.
5. Delhi, India – Projected Annual Growth Rate 2011-2025: 2.67%
India’s capital region lies on a very activity seismic zone, leaving Delhi prone to massive earthquakes. With the city growing faster than the infrastructure can keep up with, the earthquake management nonprofit Geohazards International (GHI) has focused its efforts on strengthening the people of Delhi, not the buildings. GHI currently runs two programs in Delhi, one that focuses on hospitals  and the other that works with schools, that teach administrators, engineers, and maintenance staff how to strengthen their work environment before earthquakes and how to best respond when the quake actually strikes.
The metric for growth
Some cities are expanding faster geographically than those on our list. Others are growing faster if you look at growth as a percentage of current population. However, the vast majority of world population growth over the next 15 years will take place in cities that are already massive. Our list is an attempt to identify the five cities that are experiencing the fastest growth in relation to world population, and are thus encountering issues no cities in the world have ever encountered before.
Of all the available data sets, we chose the United Nations report on world population prospects primarily for two reasons:
1) It can be extremely difficult to collect census data in cities like Sana’a and Kabul, but the United Nations has a unique breadth and depth of experience working with statistics from developing nations.
2) Unlike other data sets, United Nations’ data is transparent. Anyone can download the raw numbers to perform an independent analysis. The data also includes addendum acknowledging where estimates had to be made, or where current data was unavailable.
 All projected growth rates from http://esa.un.org/unup/pdf/WUP2011_Highlights.pdf