Resilient cities: From fail-safe to safe-to-fail

Back to top

ASU’s UREx Sustainability Research Network is exploring how extreme weather events affect urban infrastructure and how we can make cities more resilient.

Resilient cities: From fail-safe to safe-to-fail

By Kelsey Wharton

July 21, 2015

Editor's note: This story is part of a series called "Sustainable Cities" highlighting urban sustainability research across ASU.

In the early morning of September 8, 2014, rain began to fall across the Phoenix metro area. It drummed on rooftops and was soaking the ground when alarm clocks roused sleeping residents for work and school. During the Monday morning commute, the rain continued to fall in curtains and showed no signs of stopping. Soon lakes were forming in neighborhood parks and water was rushing into storm drains. Driving became treacherous—on parts of Interstate 10, people scrambled from their cars as floodwater overtook their vehicles.

When the skies cleared that afternoon, nearly half of Phoenix’s annual rainfall had been dumped on the city in a matter of hours. Infrastructure built to handle rainwater and runoff, like retention basins, storm sewers and washes, was overwhelmed. As a result, cars and homes were flooded and two people lost their lives.

map of Arizona precipitation
Percent of normal precipitation for the first week of September 2014. Phoenix received more rain in a single day than it usually gets for the entire month of September. Credit: NOAA

The chances of such a rain event occurring in Phoenix during a given year are only 0.2 percent. This is also known as a 500-year flood event because it is expected to be so rare as to occur only once during that period. Just a few weeks after the Sept. 8 rain, another storm soaked the city, a storm that only had a 1 percent chance of occurring (also known as a 100-year flood event).

As global climate change increases the frequency of extreme weather events, we may need to recalibrate our definition of “rare.”

As global climate change increases the frequency of extreme weather events, we may need to recalibrate our definition of “rare.”

In addition to urban flooding, global climate change is predicted to bring increased coastal flooding, like that associated with Hurricane Katrina and Super Storm Sandy, as well as extreme heat.

a flooded front yard in Phoenix
Parts of the Phoenix metro area, like this Tempe neighborhood, experienced flooding as a result of the September 8, 2014 deluge. Credit: Diane Boudreau.

Historically, infrastructure to mitigate flooding and heat has been designed to be fail-safe, meaning it is designed not to fail. But the concept of fail-safe can be a dangerous illusion.

“The failing in these extreme weather events was that people built and trained themselves to think that events of this magnitude will never happen,” says Charles Redman, a professor and founding director in the School of Sustainability at Arizona State University. “It happens now and we can expect them to happen more frequently in the future.”

Reimagining infrastructure

Extreme weather events can cripple the infrastructure that enables transit, electricity, water and other crucial urban services. This leaves citizens cut off and in danger. Certain groups in a city, such as those of low socioeconomic status, are often disproportionately affected.

Three ASU researchers are leading a new project designed to face these challenges and change the way we think about urban infrastructure. The Urban Resilience to Extreme Weather-Related Events Sustainability Research Network (UREx SRN) is a team of 50 researchers and practitioners from 15 different institutions.

The National Science Foundation has awarded the network $12 million over five years through its Sustainability Research Networks program, which focuses on urban sustainability. The UREx SRN is an international network that includes researchers and partner organizations across nine cities in North and South America: Portland, Oregon; Syracuse, New York, New York, New York; Baltimore, Maryland; Phoenix, Arizona; Miami, Florida, Hermosillo, Mexico, San Juan Puerto Rico; and Valdivia Chile.

“Extreme events present a great challenge to global sustainability and urban areas are particularly vulnerable to these events, often due to their location, interdependent infrastructure and people concentration,” said Georgia Kosmopoulou, Program Director in Economics at the National Science Foundation. “This SRN team will develop, through a novel more holistic approach, methods and tools to assess how infrastructure can become more resilient, providing ecosystem services, in an effort to improve social wellbeing. They will exploit new technologies promoting flexibility and adaptability in infrastructure that benefit urban populations. The geographical breadth of the proposal is an advantage; cities that represent alternative cultural backgrounds can offer new ideas about socio-ecological-technological infrastructure.”

The UREx SRN co-directors each saw a need to improve our current approach to infrastructure through the lens of their own fields. Project director Redman, an anthropologist, recognized that infrastructure does not always serve populations equally. He gives the example of retention basins, used to collect stormwater. These are developed into parks in some neighborhoods.

“When you drive around, the retention basins that have soccer fields in them are in the better neighborhoods. Yet it rains the same in other neighborhoods,” he says.

Co-director Nancy Grimm is an ecologist and professor in the School of Life Sciences. She says infrastructure that incorporates elements of the natural environment may be more effective in the long run.

“We're interested in letting a little bit more of nature back into the city. We can actually benefit quite a lot from using some of the characteristics of natural systems and incorporating those into our designs,” she says.

She points to coastal wetlands and sand dunes as examples of natural infrastructure that protect urban areas from storms and flooding. Cities should be working with, not against, their natural environments, she says.

restored marsh
Coastal ecosystems like wetlands and sand dunes can be natural buffers for cities against storm surges and flooding. This Mississippi wetland area was destroyed by Hurricane Katrina and has been restored by the Federal Emergency Management Agency. Credit: Jennifer Smits/FEMA.

Mikhail Chester, the other co-director, is an engineer and assistant professor in the School of Sustainable Engineering and the Built Environment. He had a “light bulb moment” while driving with Grimm through north Phoenix.

“Nancy said to me, ‘How do engineers use landscape design to minimize indoor heat exposure?’ I thought about it and realized that engineers don’t think about that. Landscape architects do. We realized there’s an opportunity to rethink how disciplines can come together to design infrastructure to be more resilient to extreme events,” he recalls.

When fail-safe fails

Sewage-contaminated stormwater that floods streets and pollutes drinking water sounds like a problem of developing nations. But it’s actually happening in 300 cities across the U.S. because of combined sewer overflow systems where rainwater runoff and sewage are collected in the same pipes. These systems usually deliver sewage to a treatment plant, but during times of heavy rainfall the pipe capacity is exceeded. Excess, untreated water is discharged directly into nearby streams and other bodies of water. Sometimes it overflows into the streets. (Phoenix has a divided overflow system and does not face this issue.)

“This is not a Third World problem alone,” says Redman. “Nice icons of sustainability, like Portland, which we’re studying, have combined sewer outlets. They do get floods on their streets and sometimes they are made up of sewage as well as rainfall. It’s an under-the-rug kind of issue that people in charge don’t talk about.”

We’re here to say that everything is not okay,” says Chester. “We need to find a way to build a new approach to an old problem.”

“We’re here to say that everything is not okay,” says Chester. “We need to find a way to build a new approach to an old problem.”

The UREx SRN will benefit from ASU’s history of success in interdisciplinary research and its strong focus on coupled human-natural systems and urban sustainability. This includes initiatives such as the Central Arizona-Phoenix Long-Term Ecological Research project (CAP LTER), which Grimm directs, the Julie Ann Wrigley Global Institute of Sustainability and the School of Sustainability.

Taking a holistic approach, the team will evaluate the social, ecological and technical systems (SETS) related to infrastructure. This includes recognizing the values of all stakeholders, from city decision makers to the citizens who will use and be affected by infrastructure. It also involves understanding a city’s natural environment and evaluating available technology. The result will be a suite of tools to help implement urban infrastructure that is tailored to its location and safe-to-fail.

“Fail-safe is built on a risk management principle. It’s all about how often does it happen, how potentially bad is it, who does it affect? Those are the parameters you work with and you work with acceptable levels of those parameters. It leads you to build things that are bigger and heavier,” says Redman. “Safe-to-fail has to be built on less certainty but it also has to be built on restructuring the dynamics of the system and that’s where SETS comes in. We think we need to really understand these dynamics better than people currently do.”

One example of a safe-to-fail system exists in Scottsdale, Arizona. The Indian Bend Wash Greenbelt winds through the city in a swath of green and dappled shade. A bike path and green space along the wash improve social well-being for residents in the area. Trees and plants provide numerous ecosystem services such as habitat for animals, cooler air temperatures, carbon capture and oxygen production.

After it rains, the wash fills with stormwater drained from the surrounding roads and neighborhoods. Because the wash is designed to be safe-to-fail, floodwaters do occasionally wash out the bike path and create a river instead of still ponds and grassy parks. But repairs are easily made.

Indian Bend wash in Scottsdale
Indian Bend Wash in Scottsdale is safe-to-fail resilient infrastructure. The wash is multifunctional, offering habitat for plants and animals as well as recreational areas for public use. It is designed to flood and sustain damage during heavy rains, instead of nearby neighborhoods. Credit: Nancy Grimm.

Alternatively, the Los Angeles River channel is designed to be fail-safe. Devastating flooding of the LA River in the 1800s resulted in a push to tame it. In the 1930s the river was converted – through feats of engineering and hundreds of hours of manual labor – from natural and meandering to cemented and controlled.

While directing the river through a built channel has helped to control flooding, it has also removed the ecosystem services that a river typically provides. In addition, the entire system could be paralyzed if one part of the structure sustains significant damage, such as from an earthquake. As a result, the City of Los Angeles has recently begun planning to transform parts of the river to recapture parts of the lost ecosystem.

Los Angeles River
Fail-safe infrastructure, like the Los Angeles River, does not offer the multifunctionality of resilient infrastructure. It may also be susceptible to the kinds of extreme weather events that are predicted with global climate change. Credit: U.S. Army Corps of Engineers.

Building resilience

Creating safe-to-fail infrastructure requires consideration of SETS and the current and future needs of a city. UREx SRN teams co-led by one engineer, one social scientist and one environmental scientist will be based in each partner city. This will ensure an interdisciplinary approach across the network and will produce a rich understanding of infrastructure needs and impacts across cities and cultures.

“There is a lot of opportunity to think about who is vulnerable to climate change and where they live in the city, to tailor redevelopment of infrastructure to protect the people who are the most vulnerable,” says Chester.

We’re going to build infrastructure to be more resilient and equitable and not just more efficient.”

Teams in Puerto Rico, Mexico and Chile will capture Latin American attitudes in order to understand the cultural value placed on environmental amenities and financial efficiency. This is important to the U.S. as well. Redman notes that as Latino populations continue to grow in U.S. cities, they will look increasingly like Latin American cities.

Valdivia, Chile
The city of Valdivia, Chile is part of the UREx network. Credit: Cristian Diaz.

He adds: “By bringing this all together I think we may be able to really talk to people who build the future. From the first day of designing something like highways and power grids we’re going to talk about how Earth’s systems work and how human institutions react. And we’re going to build for that.

“We’re going to build infrastructure to be more resilient and equitable and not just more efficient.”