Interdependent networks of infrastructure, ecosystems, and social systems provide essential urban goods and services (very high confidence). Damage to such networks from current weather extremes and future climate will adversely affect urban life (medium confidence). Coordinated local, state, and federal efforts can address these interconnected vulnerabilities (medium confidence).
Process for developing key messages:
Report authors developed this chapter through technical discussions of relevant evidence and expert deliberation and through regular teleconferences, meetings, and email exchanges. For additional information on the overall report process, see App. 1: Process. The author team evaluated scientific evidence from peer-reviewed literature, technical reports, and consultations with professional experts and the public via webinar and teleconferences. The scope of this chapter is urban climate change impacts, vulnerability, and response. It covers the built environment and infrastructure systems in the socioeconomic context of urban areas. This chapter updates findings from the Third National Climate Assessment and advances the understanding of previously identified urban impacts by including emerging literature on urban adaptation and emphasizing how urban social and ecological systems are related to the built environment and infrastructure. The five case-study cities were selected because they represent a geographic diversity of urban impacts from wildfire, sea level rise, heat, and inland flooding. The author team was selected based on their experiences and expertise in the urban sector. They bring a diversity of disciplinary perspectives and have a strong knowledge base for analyzing the complex ways that climate change affects the built environment, infrastructure, and urban systems.
Description of evidence base:
Research focusing on urban areas shows that climate change has or is anticipated to have a net negative effect on transportation,1
Researchers have modeled and documented how negative effects on one system that provides urban goods and services cascade into others that rely on it.17
The literature shows that coordinated resilience planning across sectors and jurisdictions to address interdependencies involves using models and plans,24
New information and remaining uncertainties:
Interconnections among urban systems have been studied less extensively than climate change effects on individual urban sectors, and there are still gaps to be filled.29
While it has been demonstrated that climate change affects urban systems, the extent to which climate change will affect a given urban system is difficult to predict. It depends on the unique strengths and vulnerabilities of that system as well as the regional and local climate conditions to which the system is exposed.35 36
The severity of future climate impacts and cascading consequences for urban networks depends on the magnitude of global climate change.39
Assessment of confidence based on evidence:
There is very high confidence that urban areas rely on essential goods and services that are vulnerable to climate change because they are part of interdependent networks of infrastructure, ecosystems, and social systems. There is high confidence that extreme weather events have resulted in adverse cascading effects across urban sectors and systems, as there is documentation of a significant number of case studies of urban areas demonstrating these effects. It is projected with medium confidence that network damages from future climate change will disrupt many aspects of urban life, given that the complexity of urban life and the many factors affecting urban resilience to climate change make future disruptions difficult to predict. Similarly, there is medium confidence that addressing interconnected vulnerabilities via coordinated efforts can build urban resilience to climate change.