Resilient cities are those that are able to master a crisis and which are
able to exit the state of crisis stronger than before. New York is a good
example. The crisis can be a war, natural catastrophes, economic
developments, or unprecedented growth, as it occurred in Europe and
North America after the industrial revolution, and as it presently occurs
in the cities North and South of the equator, where at present the
majority of the world’s population lives. Resilient cities have the capacity
to learn, to remember, and to transform findings of the past into
strategies for the future.
Sustainability is a good basis for resilience. Resilient cities have a high
degree of recycling and turn waste into new and useful materials.
Resilient cities transform urban farming, energy generation, information
sensing and processing into a lifestyle. Future new cities must be
planned for resilience. Existing cities can be transformed to become
more sustainable and resilient.

 Understanding the City
In order to make cities more resilient, we need to understand the
interacting functions of the city, as well as their influence on its people
and on the physical, built environment. The metaphor of an urban
metabolism and the concept of stocks and flows are helpful to
understand and define the factors that shape the city and make it
prospering over a long period of time. Important stocks and flows of a city
are related to its people: entering the city, living in the city, and leaving
the city; its materials, its water, its energy, its finances, the health of its
population, its density, and its information. Each one of those stocks and
flows is critical, but none of them by itself will guarantee the resilience of
the city.
Cities and Organisms
Cities are not organisms, but they bear similarities to organisms: they
have a physical presence, a metabolism, and they constantly change.
They normally start small and eventually reach a status of balance or
maturity. They can grow and prosper, degrade and die. Yet each of
these phases can be radically different from known organisms. Although
more than half of the world‘s population lives in urbanized areas, today‘s
cities are not sustainable. Their resilience greatly depends on the
factors that led to their establishment and on the forces that drive them.
But it mostly relies on the initiative, ingenuity and adaptability of its
people. Detroit is a striking example for this observation.
Resilient Urban Patterns
Few cities today are designed and built from scratch, and few of those
are successful immediately. Examples are Brasilia, Chandigarh or
Masdar. Instead, a city develops under the constant interaction with its
changing environment, starting from the choice of its site and the
preconditions that can foster or hinder its development. Sustainable
cities consist of sustainable urban patterns. Resilient cities display
resilient urban patterns. Sustainability and resilience are interrelated, and
design planning must be based on the knowledge of context-based best
practice for sustainable and resilient urban patterns.
Sensing, Sourcing and Urban Big Data
In the past, city planners used geometric and mathematical rules to
design, engineer, and build the city. Cities were expected to function
and grow for a long period of time. Rarely were they planned for
constant interaction with their increasingly independent and mobile
citizens who demand changes. Today, crowdsourcing and sensing
provide powerful instruments to dynamically influence the design and
management of cities. This applies mostly to existing urban systems with
a large number of people with smart phones, who actively influence the
development of their city. Cities are also installing an increasing number
of sensors that are able to monitor the day-to-day operations, as well as
to alert with regard to expected natural or other threats. Sensing and
sourcing also lead to Urban Big Data. The combination of crowd
sourcing and urban sensing can increase the resilience of cities, but only
if the necessary governance precautions are taken to avoid the misuse
of the sensing and sourcing data.
Prosperous and Resilient or Poor and Vulnerable
The selection of a suitable site for a city and its original governance set
up has long lasting influence on its performance. Depending on the
degree to which the city forms as the result of communal effort under
good governance, it will become prosperous and resilient and achieve a
high degree of livability, thus making it attractive for sustainable growth.
But if the city is built for a single dimensional purpose, encouraging a
monoculture and not encouraging diversity, chances are that it will
become poor and vulnerable as soon as the conditions for its original
success change. Therefore, diversity is a crucial precondition for resilient
future cities.