Building resilient cities


Skip Derra

The flooding in Houston was exacerbated by how the city was built. Like many cities, Houston basically paved over the existing landscape, a grassy plain that evolved to handle large rainfalls by acting like a sponge.

New ideas on how to build more resilient cities focus on working with nature, rather than trying to master it, says Arizona State University Professor Charles Redman, the founding director of ASU’s School of Sustainability and a distinguished scientist in ASU’s Julie Ann Wrigley Global Institute of Sustainability.

What this means, Redman says, is building infrastructure systems that are safe-to-fail, rather than fail-safe, and recognizing that the city should be able to take advantage of natural features of the land rather than to solidify it with concrete.

Redman leads a group of researchers from 15 institutions in a National Science Foundation-sponsored project called the Urban Resilience to Extreme Weather Related Events Sustainability Research Network (UREx SRN), which focuses on ways to make cities more resilient to natural calamities.

Here, he talks about how cities can be better prepared to withstand natural calamities.

Question: What can cities do to be better prepared for events like Harvey and Irma?

Answer: There are two areas of improvement, the first being altering the nature of the “hard” infrastructure, and second to enrich and make more effective the “soft” infrastructure of organization, cooperation, information flow, etc.

The overarching problem with cities like Houston is that they have built over the natural landscape with impervious surfaces, and with impediments to the natural flow of surface runoff. A more effective approach may be to implement infrastructure systems that work with the land to facilitate runoff rather than try to control it, but acknowledge and plan that if a specific threshold is exceeded and the system “fails” in some sense there are backup plans in place that minimize the adverse impacts.

Q: How does a safe-to-fail system operate vs. a fail-safe system?

A: This is about managing risk in an increasingly uncertain world. The fail-safe system assumes you know what is coming and that it can be handled if we build a big enough dam, levee, pipe, sea wall, etc., for protection. The problem is that many extreme events such as Katrina, Fukushima, Sandy and now Harvey go beyond the expected and result in disaster. A fail-safe approach seeks to totally prevent harm related to the weather event; however, if the event does exceed the design of the infrastructure there is little back up protection and disaster ensues.

In each case, much of the disaster might have been avoided or at least minimized through more effective awareness of the threats, better planning and well-thought-out responses. This is at the heart of the safe-to-fail approach that accepts the possibility that the hard infrastructure might be insufficient and has multiple back-up plans to ameliorate the impact. Using green infrastructure with secondary benefits, relying on multiple approaches, and moving people out of harm’s way are among the approaches to minimize negative impacts.

Q: What are some of the “soft” infrastructure approaches to becoming more resilient?

A: Short of changing the physical structure of the city, “safe-to-fail” strategies would focus on how the city prepares and responds to weather-related extreme events. The first is to map the relative vulnerability of people in different locations of the city, and as the event approaches the rescue teams don’t have to wait for 911 calls but can focus on the most likely areas to flood before the disaster develops. 

The second is to develop a system of refuge centers that are appropriate to the scale of the potential dislocation and pre-plan strategies for getting people there. In Houston planned shelters were a fraction of the size needed. A separate issue is that two of the Houston’s reservoirs threatened to overtop their embankments. It is a common mismanagement problem that reservoirs are kept too full in order to maximize available water when they should be kept lower during hurricane season.

Q: What are some of the tools being developed in the UREx SRN program?

A: We are focusing on a variety of tools, and more, to build a method of bringing together the diverse elements of city government with relevant citizen groups to plan for future hard and soft infrastructure. Primary among the tools are a variety of green infrastructure constructions that take advantage of natural ecosystem services to ameliorate the impact of extreme weather events and then, in between events, to provide desired amenities like greenbelts and recreation fields. We are also constructing maps of populations most vulnerable to various types of extreme events and systems to minimize the impact on these populations.

Q: How does the program make cities more resilient?

A: We believe there are basic steps in gathering information, planning for the scale and intensity of events that were not common in the past, but are expected more today and in the future. We want to create planning templates that will ensure that cities are more “resilient-ready” to floods, heatwaves, droughts and other weather-related extreme events.

Another category of action that will enhance the capacity of a city to handle extreme events is to build the cooperative attitude of helping each other and working together to face the challenge rather than relying totally on outside interventions. Community members working together is the best line of defense to extreme events and can leverage and fill in with the outside interventions.


Top photo: Soldiers with the Texas Army National Guard move through flooded Houston streets as floodwaters from Hurricane Harvey continued to rise Aug. 28. More than 12,000 members of the Texas National Guard were been called out to support local authorities in response to the storm. Photo by U.S. Army photo by 1st Lt. Zachary West [Public domain], via Wikimedia Commons