Designing with nature to adapt to climate change

Warmer temperatures as a result of climate change can cause unprecedented changes in rainfall, leading to more frequent flooding in many areas. This increased flooding can put pressure on transportation infrastructure located next to rivers and waterways, including roads, bridges, and embankments. Unlike traditional networks, transportation infrastructure associated with rivers and their surrounding landscapes face additional risks—like erosion and the lateral migration of rivers—that can intensify under climate change. 

Fortunately, countermeasures such as nature-based solutions (NBS) can leverage the use of natural materials and landscape features in addition to engineered structures to adapt transportation infrastructure to climate change, thereby benefiting both people and the environment. This hybrid approach of using “gray” aspects (e.g. human-made structures, like retaining walls) combined with “green” elements (e.g. natural formations, like vegetation) can be effective in mitigating flooding while enhancing environmental, social, and economic well-being. 

Nature-based solutions can help protect infrastructure against climate impacts, and more government support is needed for these types of projects.

Costa Samaras, Professor, Civil and Environmental Engineering

In a new perspective paper published in NPJ Urban Sustainability, a Nature Partner Journal, researchers at Carnegie Mellon found NBS can help improve climate resilience of  transportation infrastructure in riverine environments in the United States.

“Historically, engineers did not immediately look to nature-based solutions as an opportunity to improve transportation infrastructure resilience. With more awareness and growing experience, many State Departments of Transportation are now designing with nature,” said Marissa Webber, lead author of the paper.

Webber completed this research as part of her Ph.D. in civil and environmental engineering in 2024 and is now a postdoctoral research associate in the department of Earth Marine and Environmental Sciences at the University of North Carolina at Chapel Hill.

The team reviewed publicly available reports, documents, or projects that include riverine NBS for transportation infrastructure in the U.S. For each project, researchers identified the NBS strategy or approach, the total cost, year and location the project took place, and the size of the project. The CMU researchers also identified and summarized challenges to implementing NBS based on these documents and conversations with stakeholders in U.S. State Departments of Transportation. 

Out of the 91 projects categorized in 21 states, the study found that the most common example of NBS in their sample was riparian vegetation, which was used in 58 projects from 16 states. Riparian vegetation refers to the plants that grow alongside a river and can be used to help prevent erosion and mitigate flooding by slowing water flow. 

The second most common example of NBS used was engineered log jams, which was used in 21 projects from eight states. These human-made structures replicate naturally occurring log jams and help stabilize riverbanks, thereby reducing flood risk. 

Despite the increase in riverine NBS projects over time, this analysis of current literature yielded multiple implementation challenges when using NBS to increase the resilience of transportation infrastructure. Challenges like policy and regulation obstacles, including inflexible funding, contracting, or permitting processes, suggest a greater need for collaboration among stakeholders at all levels of government. 

“Nature-based solutions can help protect transportation infrastructure against climate impacts, and more federal, state, and local government support is needed for these types of projects,” said Costa Samaras, professor of civil and environmental engineering and director of the Scott Institute for Energy Innovation.

In response to the challenges identified, researchers propose three action items to direct future research in support of riverine NBS to improve resilience of transportation infrastructure under climate change.
First, researchers recommend further education and outreach through the collaborative efforts of both technical and nontechnical stakeholders to produce reports that highlight the successes and challenges of riverine NBS. Additionally, updated cost-benefit analyses must be performed to include the co-benefits of riverine NBS and consider the direct and indirect effects of climate change. Finally, federal and state programs should look to the successful examples set by local governance when it comes to funding and contracting agreements for riverine NBS projects. 

With this action-oriented research agenda, future work to expand NBS could simultaneously advance social and environmental justice through community engagement, to improve climate resilience in disadvantaged communities.

“Existing projects have shown that riverine NBS can serve as strategic investments to enhance the resilience of transportation infrastructure,” said Webber. “To fully realize the co-benefits of riverine NBS, coordinated actions and collaborative strategies are needed to address technical challenges, bridge institutional divides, and promote inclusive decision-making.” 

Alumna Lillian Mei (CEE ’24) also contributed to this work as a co-author through the Department of Civil and Environmental Engineering's Undergraduate Research Program.