Thames barrier, London / The Greenwich Phantom

"Urban resilience can be defined as the capacity of the system of cities to survive, adapt, and grow no matter what acute shocks occur," said Judith Rodin, president of The Rockefeller Foundation at the World Urban Forum in Medellin, Colombia. "There have always been shocks throughout history, but, today, they are different — with globalization, climate change, and the immense scale and pace of shocks." Rodin said shocks are occurring in cities based in increasingly fragile ecosystems, which puts people at unprecedented risk.

On Medellin, which is increasingly viewed as a model of a sustainable city, Rodin said the city's ability to innovate and incorporate new ideas about its infrastructure shows that it's becoming a more resilient city. "Medellin was trapped in a cycle of violence and mass incarceration, but it had the capacity to think differently." Medellin's city leadership worked on connecting its poor, isolated communities through new transit, libraries, and parks, bringing them into the mainstream. She said this was critical because the poor and vulnerable are the ones who are always most impacted.

Perhaps Rodin's central point was that "we can't always predict or prevent catastrophes, but we can control the physical and spiritual damage. It's not just about how a city operates on its best days, but whether it can operate on its worst."

So how can cities become more resilient? They have to make "an up-front investment." While those up-front investments in resilience can be expensive, they can create jobs and improve social cohesion. Improving resilience is not just a task for the public sector either. "Businesses have self interest in becoming involved, too." Rodin pointed to a World Bank study that argued 25 percent of all businesses that fail after a major disruption don't reopen.

New technology may also provide hope. "Look at the advances in 3D-printing, which enable us to print parts when distribution systems break down, or on-site manufacturing of emergency shelters."

To bolster the ability of cities to adapt to changing circumstances, the Rockefeller Foundation announced it will dedicate $100 million to its new 100 Resilient Cities program. By increasing the focus on resilience among 100 world cities, the foundation hopes to create a market for resilient products and services, so more companies have an incentive to serve this market. Cities can use the foundation's funds to find chief resilient officers, who will be charged with creating a city-wide resilience strategy.

Other global experts also weighed in on the move towards urban resilience. Katherine Vines, C40 Cities Climate Leadership Group, which includes 40 of the 50 largest cities in the world, said mega-cities face a "huge job adapting to climate change, shocks, and chronic stresses." A recent report by the group found that 82 percent of C40 cites are already dedicating staff and funds to urban resilience, including early warning systems and emergency preparedness, and green infrastructure systems, like green roofs and permeable pavements, in order to cool cities and deal with flooding.

As an example, she point to Rio de Janeiro, where Mayor Eduardo Paes is implementing a robust resilience strategy, with an emergency response center, long-term climate risk assessment, and actual construction work to improve slope support and drainage. And there's also a real human component to the efforts: "Part of the emergency warning system will involve training local nurses." Vines also mentioned an innovative new "rains app" from the city of Sao Paulo, which enables local residents to see their risk of summertime flooding in real time.

And then Stefan Denig, Siemens Sustainable City program, offered some scary data. Due to flooding in the 1950s, London spent $8 billion on its huge Thames barrier. Over the next few decades, London only had use the gates twice. However, in the past decade, the city had use the gates 40 times. It's expected the city will soon need to use the gates up to 30 times per year.

While heavy infrastructure like London's Thames barrier are critical, unfortunately, not all cities can afford the expense. Denig said Ho Chi Minh in Vietnam would need a 170-kilometer-long dam to really protect itself but "no one has the money for that," so they have to use other approaches.

Resilience will then cost money, which is difficult given cities face so many competing demands for limited funds. What costs is creating redundant systems. For example, London's subway, the tube, has its own power generation system in case the city's system fails. "This is high cost and used rarely."