Adaptive City Planning Tackles the Uncertainty of Sea Level Rise

By Liza Moriconi

Historically, engineers have designed cities’ infrastructure to a baseline climate. However, given the inevitability of and rapid acceleration of climate change, this baseline is shifting. “Sea levels along the United States coastline are projected to rise a foot on average over the next three decades, which is equivalent to the total rise we’ve seen over the last 100 years,” notes D.J. Rasmussen, a climate change risk & resilience consultant in global built environment consulting firm Arup’s San Francisco office. “Because of the inertia of contributing factors, including increasing global temperatures associated with greenhouse gas emissions, coastal floods will become an inevitable problem for hundreds of millions of people living in low lying areas for centuries to come.” 

To provide proactive planning measures, Arup uses a resilience-focused planning approach called “Flexible Adaptation Pathways,” which focuses on providing dynamic and adaptive planning solutions for many climate-change-related uncertainties. “Flexible Adaptation Pathways are often compared to a subway map because they can offer multiple routes to arrive at the same destination,” says Jack Hogan, a senior risk and resilience engineer in Arup’s San Francisco office. “In some ways, a static planning process can be destined to fail. Instead of trying to predict the water level in 100 years, this approach provides the opportunity to change course and switch from one strategy to another as we gather more climate data to achieve the least potential regret.”  The adaptive planning approach recognizes that every situation is different, and there may be better defensive approaches suitable for different projects. “Deliberate adaptive planning is entirely different from how leaders have approached natural hazard preparedness. Instead of implementing a solution and forgetting about the problem until something goes wrong again, Flexible Adaptation Pathways keep attention on the issue over time,” adds Rasmussen. Flexible Adaptation Pathways chart specific decision outcomes on a timeline for infrastructure planners to visualize how something, like a seawall or levee, might perform against different sea level rise scenarios. It can also provide insight into when a specific infrastructure investment should be made or when a switch should be made to another strategy. 

In developing coastal resilience, there are three main strategies a city might look to: resisting, restoring, and retreating. These solutions are not mutually exclusive, and using a hybrid approach typically provides the best line of defense against sea level rise. Resisting includes defining a specific level of protection, restoring includes implementing nature-based solutions, and retreating includes pulling back from the shoreline. “Making these decisions is a result of a robust engagement process with stakeholders and community groups, especially with public projects,” says Vincent Lee, an associate principal and Global Water Skills Leader in Arup’s New York office. “With one of the waterfront developments we supported New York City in developing, a portion of the waterfront used a resist strategy to protect visitors in the public space and the residents in new housing. In another part of the park, Arup used a restore approach to cultivate coastal wetlands, providing benefits to both the natural environment and New Yorkers seeking refuge from the concrete jungle.” 

With long term planning, using a hybrid strategy provides a variety of options for infrastructure planners. Arup is also contributing to various planning projects that are connected to a large-scale transportation infrastructure project geared toward urbanizing Honolulu in an efficient and resilient way. Recently, they worked on a masterplan for a new transit-oriented development in Honolulu, which creates a linear park out of an existing flood control canal. “You wouldn’t know if you looked at it, but the park design is providing an increased level of protection for the area by embedding a seawall underneath the landscape,” shares Hogan. “This work couples resilience with revitalization and sustainable transportation. I love to see projects that are not only proactive in putting infrastructure in place to defend against the worst to come with climate change, but that also achieves other co-benefits and enhances the public realm at the same time.”

When deciding which pathway is the best proactive method to protect against sea level rise, infrastructure planners must take into account the option with the least potential regret. The goal is to avoid a “stranded asset,” or an infrastructure investment that did not survive the entirety of its intended lifecycle. The Flexible Adaptation Pathways approach supplies options for making infrastructure investments that are flexible, to better stand the test of time and avoid potential regrets. Flexibility is an ideal planning parameter that is paramount in climate change adaptation. “Superstorm Sandy was a wakeup call for New York City,” says Lee. “We’ve started to see a fundamental shift in the way cities are addressing climate change adaptation.” With the uncertainty of the potential effects of climate change, investing in a plan that can be easily adapted provides the greatest potential for success. “There is an ethos in adaptation planning that embraces the process rather than the outcome,” notes Hogan. The Flexible Adaptation Pathways method addresses continuing adaptation plans by monitoring decisions outcomes and growing or altering options as new challenges arise. “Last summer, Hurricane Henri came through New York City and broke the rainfall record in New York City, and then Hurricane Ida hit a couple weeks later and broke Henri’s record,” says Lee. “It’s not just people living near the floodplain, Ida exposed aging and undersized infrastructure that was designed for a different climate.” The Flexible Adaptation Pathways method allows for a response strategy to better react to unexpected challenges that may arise in the future. 

Overall, proactive planning against sea level rise and other threats posed by climate change provides a much better response strategy than reactive planning. Arup aims to supply infrastructure planners with the toolkit they need to defend their cities from sea level rise. Hopefully, this will ignite a fundamental shift in the way cities across the world address climate change adaptation, as there is much more to protect cities from than just sea level rise. Sea level rise is just one example of the effects that climate change will have on our world, and since it’s not a question of if, but when, we need to have all the tools necessary to adapt to any and all threats. 

Liza Moriconi is an intern for Civil + Structural Engineer Media, as well as a senior Civil Engineering student at the University of Arkansas. She can be reached at lmoriconi@zweiggroup.com.

*This article was originally published in April 2022