The opportunities and resources in urban areas are critically important to the health and well-being of people who work, live, and visit there. Climate change can exacerbate existing challenges to urban quality of life, including social inequality, aging and deteriorating infrastructure, and stressed ecosystems. Many cities are engaging in creative problem solving to improve quality of life while simultaneously addressing climate change impacts.
Damages from extreme weather events demonstrate current urban infrastructure vulnerabilities. With its long service life, urban infrastructure must be able to endure a future climate that is different from the past. Forward-looking design informs investment in reliable infrastructure that can withstand ongoing and future climate risks.
Interdependent networks of infrastructure, ecosystems, and social systems provide essential urban goods and services. Damage to such networks from current weather extremes and future climate will adversely affect urban life. Coordinated local, state, and federal efforts can address these interconnected vulnerabilities.
Cities across the United States are leading efforts to respond to climate change. Urban adaptation and mitigation actions can affect current and projected impacts of climate change and provide near-term benefits. Challenges to implementing these plans remain. Cities can build on local knowledge and risk management approaches, integrate social equity concerns, and join multicity networks to begin to address these challenges.
The opportunities and resources in urban areas are critically important to the health and well-being of people who work, live, and visit there. Climate change can exacerbate existing challenges to urban quality of life, including social inequality, aging and deteriorating infrastructure, and stressed ecosystems. Many cities are engaging in creative problem solving to improve quality of life while simultaneously addressing climate change impacts.
Damages from extreme weather events demonstrate current urban infrastructure vulnerabilities. With its long service life, urban infrastructure must be able to endure a future climate that is different from the past. Forward-looking design informs investment in reliable infrastructure that can withstand ongoing and future climate risks.
Interdependent networks of infrastructure, ecosystems, and social systems provide essential urban goods and services. Damage to such networks from current weather extremes and future climate will adversely affect urban life. Coordinated local, state, and federal efforts can address these interconnected vulnerabilities.
Cities across the United States are leading efforts to respond to climate change. Urban adaptation and mitigation actions can affect current and projected impacts of climate change and provide near-term benefits. Challenges to implementing these plans remain. Cities can build on local knowledge and risk management approaches, integrate social equity concerns, and join multicity networks to begin to address these challenges.
Virtually Certain | Extremely Likely | Very Likely | Likely | About as Likely as Not | Unlikely | Very Unikely | Extremely Unlikely | Exceptionally Unlikely |
---|---|---|---|---|---|---|---|---|
99%–100% | 95%–100% | 90%–100% | 66%-100% | 33%-66% | 0%-33% | 0%-10% | 0%-5% | 0%-1% |
Very High | Hoch | Medium | Niedrig |
---|---|---|---|
Strong evidence (established theory, multiple sources, consistent results, well documented and accepted methods, etc.), high consensus | Moderate evidence (several sources, some consistency, methods vary and/or documentation limited, etc.), medium consensus | Suggestive evidence (a few sources, limited consistency, models incomplete, methods emerging, etc.), competing schools of thought | Inconclusive evidence (limited sources, extrapolations, inconsistent findings, poor documentation and/or methods not tested, etc.), disagreement or lack of opinions among experts |
Documenting Uncertainty: This assessment relies on two metrics to communicate the degree of certainty in Key Findings. See Guide to this Report for more on assessments of likelihood and confidence.
Urban areas, where the vast majority of Americans live, are engines of economic growth and contain land valued at trillions of dollars. Cities around the United States face a number of challenges to prosperity, such as social inequality, aging and deteriorating infrastructure, and stressed ecosystems. These social, infrastructure, and environmental challenges affect urban exposure and susceptibility to climate change effects.
Urban areas are already experiencing the effects of climate change. Cities differ across regions in the acute and chronic climate stressors they are exposed to and how these stressors interact with local geographic characteristics. Cities are already subject to higher surface temperatures because of the urban heat island effect, which is projected to get stronger. Recent extreme weather events reveal the vulnerability of the built environment (infrastructure such as residential and commercial buildings, transportation, communications, energy, water systems, parks, streets, and landscaping) and its importance to how people live, study, recreate, and work. Heat waves and heavy rainfalls are expected to increase in frequency and intensity. The way city residents respond to such incidents depends on their understanding of risk, their way of life, access to resources, and the communities to which they belong. Infrastructure designed for historical climate trends is vulnerable to future weather extremes and climate change. Investing in forward-looking design can help ensure that infrastructure performs acceptably under changing climate conditions.
Urban areas are linked to local, regional, and global systems. Situations where multiple climate stressors simultaneously affect multiple city sectors, either directly or through system connections, are expected to become more common. When climate stressors affect one sector, cascading effects on other sectors increase risks to residents’ health and well-being. Cities across the Nation are taking action in response to climate change. U.S. cities are at the forefront of reducing greenhouse gas emissions and many have begun adaptation planning. These actions build urban resilience to climate change.
<b>Maxwell</b>, K., S. Julius, A. Grambsch, A. Kosmal, L. Larson, and N. Sonti, 2018: Built Environment, Urban Systems, and Cities. In <i>Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II</i> [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 438–478. doi: 10.7930/NCA4.2018.CH11
Recent extreme weather events reveal the vulnerability of the built environment (infrastructure, such as residential and commercial buildings, transportation, communications, energy, water systems, parks, streets, and landscaping) and its importance to how people live, study, recreate, and work in cities. This chapter builds on previous assessments of urban social vulnerability and climate change impacts on urban systems.1,2,3 It discusses recent science on urban social and ecological systems underlying vulnerability, impacts on urban quality of life and well-being, and urban adaptation. It also reviews the increase in urban adaptation activities, including investment, design, and institutional practices to manage risk. Examples of climate impacts and responses from five cities (Charleston, South Carolina; Dubuque, Iowa; Fort Collins, Colorado; Phoenix, Arizona; and Pittsburgh, Pennsylvania) illustrate the diversity of American cities and the climate risks they face.
Urban areas in the United States, where the vast majority of Americans live, are engines of economic growth and contain land valued at trillions of dollars. In 2015, nearly 275 million people (about 85% of the total U.S. population) lived in metropolitan areas, and 27 million (about 8%) lived in smaller micropolitan areas.4 Metropolitan areas accounted for approximately 91% of U.S. gross domestic product (GDP) in 2015, with over 23% coming from the five largest cities alone.5 Urban land values are estimated at more than two times the 2006 national GDP.6 Urbanization trends are expected to continue (Figure 11.1), and projections suggest that between 425 and 696 million people will live in metropolitan and micropolitan areas combined by 2100.7 All of these factors affect how urban areas respond to climate change.
Cities around the United States face a number of challenges to prosperity, such as social inequality, aging and deteriorating infrastructure, and stressed ecosystems. Urban social inequality is evident in disparities in per capita income, exposure to violence and environmental hazards, and access to food, services, transportation, outdoor space, and walkable neighborhoods.9,10,11,12 Cities are connected by networks of infrastructure, much of which is in need of repair or replacement. Failing to address aging and deteriorating infrastructure is expected to cost the U.S. GDP as much as $3.9 trillion (in 2015 dollars) by 2025.13 Current infrastructure and building design standards do not take future climate trends into account.14 Urbanization affects air, water, and soil quality and increases impervious surface cover (such as cement and asphalt).15,16,17 Urban forests, open space, and waterways provide multiple benefits, but many are under stress because of land-use change, invasive species, and pollution.18 These social, infrastructure, and environmental challenges affect urban exposure and susceptibility to climate change effects.
Urban areas, where the majority of the U.S. population lives and most consumption occurs, are the source of approximately 80% of North American human-caused greenhouse gas (GHG) emissions, despite only occupying 1%–5% of the land. Therefore, changes to urban activities can have a significant impact on national GHG emissions.19 Land use and land-cover change contribute to radiative forcing, and infrastructure design can lock in fossil fuel dependency, so urban development patterns will continue to affect carbon sources and sinks in the future (Ch. 5: Land Changes).19,20,21 Many cities in the United States are working to reduce their GHG emissions and can be key leverage points in mitigation efforts.
Urban areas in the United States are already experiencing the effects of climate change. Across regions, U.S. cities differ in the acute and chronic climate stressors they are exposed to and how these stressors interact with local geographic characteristics.1 In coastal areas, the built environment is subject to storm surge, high tide flooding, and saltwater intrusion (Ch. 8: Coastal, KM 1). Wildfires are on the rise in the West, lowering air quality and damaging property in cities near the wildland–urban interface (Ch. 6: Forests, KM 1; Ch. 13: Air Quality, KM 2; Ch. 14: Human Health, KM 1; Ch. 24: Northwest, KM 3; Ch. 25: Southwest, KM 2). In 2017, Los Angeles witnessed the largest wildfire in its history, with over 700 residents ordered to evacuate. The fire began during a heat wave and burned over 7,100 acres.22 Key climate threats in the Northeast, on the other hand, are from precipitation and flooding: between 2007 and 2013, Pittsburgh experienced 11 significant flash flooding events23,24 (Ch. 18: Northeast, KM 3). Heat waves (Figure 11.2) and heavy rainfalls (Figure 11.3) are expected to increase in frequency and intensity (Ch. 2: Climate KM 2 and 5).25,26,27 The way city residents respond to such incidents depends on their understanding of risk, their way of life, access to resources, and the communities to which they belong.28
In other parts of the country, drought conditions coupled with extreme heat increase wildfire risk, and rainfall after wildfires raises flood risks.21 In 2012 and 2013, fires destroyed hundreds of homes in the Fort Collins area of the Northern Great Plains region. In those same years, floods washed out transportation infrastructure and caused $2 billion (in 2013 dollars) in total damages.34,35
Despite these differences, U.S. cities experience some climate impacts in similar ways. For example, prolonged periods of high heat affect urban areas around the country.21 Cities are already subject to higher surface temperatures because of the urban heat island (UHI) effect, which can also affect regional climate.29 The UHI is projected to get stronger with climate change.29 Another commonality is that most cities are subject to more than one climate stressor. Exposure to multiple climate impacts at once affects multiple urban sectors, and the results can be devastating.30 Over a four-day period in 2015, the coastal city of Charleston in the Southeast region experienced extreme rainfall, higher sea levels, and high tide flooding. These impacts combined to cause dam failures, bridge and road closures, power outages, damages to homes and businesses, and a near shutdown of the local economy (Ch. 19: Southeast, KM 2).31,32,33 These kinds of incidents are expected to continue as climate change brings a higher number of intense hurricanes, high tide flooding, and accelerated sea level rise (Ch. 8: Coastal, KM 1).21
Another similarity cities share is that when climate stressors affect one city sector, cascading effects on other sectors increase risks to residents’ health and well-being (Ch. 17: Complex Systems). Higher temperatures can increase energy loads, which in turn can lead to structural failures in energy infrastructure, raise energy bills, and increase the occurrence of power outages (Ch. 4: Energy, KM 1). These changes strain household budgets, increase people’s exposure to heat, and limit the delivery of medical and social services. For all cities, the duration of exposure to a climate stressor determines the degree of impacts. In recent years in the Southwest region, California experienced exceptional drought conditions. Urban and rural areas saw forced water reallocations and mandatory water-use reductions. Utilities had to cut back on electricity production from hydropower because of insufficient surface water flows and water in surface reservoirs (Ch. 25: Southwest, KM 1 and 5).36,37,38
Urban areas are linked to local, regional, and global systems.39,40,41 For example, changes in regional food production and global trade affect local food availability.42 Likewise, urban electricity supply often relies on far-off reservoirs, generators, and grids. Situations where multiple climate stressors simultaneously affect multiple city sectors, either directly or through system connections, are expected to become more common.12,43,44
Cities in all regions of the country are undertaking adaptation and mitigation actions. Several cities have climate action plans in place (see Bierbaum et al. 2013 for a review of U.S. urban adaptation plans45). Pittsburgh made commitments to reduce GHG emissions. Fort Collins initiated the Fort Collins ClimateWise Program. Phoenix is taking measures to reduce the UHI effect. These actions build urban resilience to climate change.
Cities are places where people learn, socialize, recreate, work, and live together. Quality of life for urban residents is associated with social and economic diversity, livelihood opportunities, and access to education, nature, recreation, healthcare, arts, and culture. Urban areas can foster economic prosperity and a sense of place. Yet, many cities in the United States face challenges to prosperity, including social inequality, aging and deteriorating infrastructure, and stressed ecosystems (Ch. 18: Northeast, KM 3).13,18,46 These problems are intertwined. Climate change impacts exacerbate existing challenges to urban quality of life and adversely affect urban health and well-being.
Urban populations experiencing socioeconomic inequality or health problems have greater exposure and susceptibility to climate change.12,47 Climate susceptibility varies by neighborhood, housing situation, age, occupation, and daily activities. People without access to housing with sufficient insulation and air conditioning (for example, renters and the homeless) have greater exposure to heat stress. Children playing outside, seniors living alone, construction workers, and athletes are also vulnerable to extreme heat (Figure 11.4).12,48
In addition to temperature extremes, climate change adversely affects urban population health through air and water quality and vector-borne diseases (Ch. 14: Human Health, KM 1). Urban residents feel economic impacts from food price volatility and the costs of insurance, energy, and water.12,50 Climate change also threatens the integrity of personal property, ecosystems, historic landmarks, playgrounds, and cultural sites such as libraries and museums, all of which support an urban sense of place and quality of life (Ch. 24: Northwest, KM 2).51,52,53 For example, historic landmarks in Charleston are at risk from sea level rise.54 Urban ecosystems are further stressed by often unpredictable climate-related changes to tree species ranges, water cycles, and pest regimes.55
Coastal city flooding can result in forced evacuation, adversely affecting family and community stability, as well as mental and physical health (Ch. 14: Human Health, KM 1).12 It also poses significant challenges to inland urban areas receiving these populations.56,57 Many cities are undertaking creative problem solving to address climate change impacts and quality of life. They use approaches from urban design, sustainability, and climate justice.58,59,60 For example, New York City’s Trees for Public Health program targets street tree planting in neighborhoods of greatest need to improve the UHI effect, asthma rates, crime rates, and property values.61
Urban infrastructure needs to perform reliably throughout its long service life. Infrastructure designed for historical climate trends is more vulnerable to future weather extremes and climate change. Impacts include changes in building enclosure vapor drive, energy performance, and corrosion of structures.14,62 Above- and below-grade transportation systems are at increased risk from flooding and degradation that reduces expected service life (Ch. 12: Transportation, KM 1). Higher temperatures increase stress on cooling systems to perform as designed. High indoor temperatures reduce thermal comfort and office worker productivity, potentially requiring building closures. Over time, sea level rise and flooding are expected to destroy, or make unusable, properties and public infrastructure in many U.S. coastal cities (Ch. 8: Coastal, KM 1). Investor costs increase when infrastructure is degraded, damaged, or abandoned ahead of its anticipated useful life.63,64
Damages from extreme weather events demonstrate existing infrastructure vulnerabilities. Long-term, gradual risks such as sea level rise further exacerbate these vulnerabilities. Current levels of infrastructure investment in the United States are not enough to cover needed repairs and replacement.13 Infrastructure age and disrepair make failure or interrupted service from extreme weather even more likely.13 Heavy rainfall during Arizona’s 2014 monsoon season shut down freeways and city streets in Phoenix because key pumping stations failed.65 Climate change has already altered the likelihood and intensity of some extreme events, and there is emerging evidence that many types of extreme events will increase in intensity, duration, and frequency in the future.27,66,67,68,69 Projecting specific changes in extreme events in particular places remains a challenge.
Costs are felt nationally as business operations, production inputs, and supply chains are affected.70,71 Higher temperatures reduce labor productivity in construction and other outdoor industries.12,44,72,73 Upgrades to buildings and the electrical grid are needed to handle higher temperatures.74,75,76 Risk portfolios in the housing finance, municipal bond, and insurance industries may need to be adjusted.44,72,77 Forward-looking design and risk management approaches support the achievement of design and investment performance goals.78,79,80,81
Incorporating climate projections into infrastructure design, investment and appraisal criteria, and model building codes is uncommon.82,83,84,85,86,87,88,89 Standardized methodologies do not exist,62,90,91,92 and the incorporation of climate projections is not required in the education or licensing of U.S. design, investment, or appraisal professionals.80,93,94,95 Building codes and rating systems tend to be focused on current short-term, extreme weather. Investment and design standards, professional education and licensing, building codes, and zoning that use forward-looking design can protect urban assets and limit investor risk exposure.83,96,97,98
A handful of cities have begun to take a longer-term view toward planning.99,100,101 These cities have developed adaptation plans, resilience guidelines, and risk-informed frameworks. However, they do not yet have a portfolio of completed projects.59,102 Adaptation planning is not always informed by technical analysis of changing hazards, climate vulnerability assessments, and monitoring and control systems.79 U.S. cities can examine methods and learn from completed projects, such as those developed by Engineers Canada and UKCIP Design for Future Climate.62,90 Managing climate risks promotes the integrity, efficiency, and safety of infrastructure to ensure reliable performance over the infrastructure’s service life.14,81
The essential goods and services that form the backbone of urban life are increasingly vulnerable to climate change. Cities are hubs of production and consumption of goods, and they are enmeshed in regional-to-global supply chains. They rely on local services and interdependent networks for telecommunications, energy, water, healthcare, transportation, and more (Ch. 4: Energy, KM 1; Ch. 3: Water, KM 1; Ch. 14: Human Health, KM 2; Ch. 12: Transportation, KM 2; Ch. 17: Complex Systems, KM 1). Gradual and abrupt climate changes disrupt the flow of these goods and services.44 For example, the 2012 High Park Fire in Colorado had wide-reaching impacts on air and water quality. The city of Fort Collins experienced air quality that was seven times worse than the daily average (Ch. 13: Air Quality, KM 2).103 Storms washed ash and debris into the Cache la Poudre River, polluting the city’s drinking water source for residents and industries.104 In another example, two inches of rain fell in a single hour in Pittsburgh in August 2011. Four people died in the resulting flash flood. Impervious surfaces and combined sewer systems contribute to urban flash flooding risks (Figure 11.5).105 For similar examples of cascading impacts, see Chapter 17: Complex Systems, Box 17.1 on Hurricane Harvey and Box 17.5 on the 2003 Northeast Blackout. Figure 11.6 describes how heavy rainfalls, which are projected to increase with climate change, can disrupt the flow of goods and services to urban residents through increased runoff and localized flooding.
As interconnections among sectors increase, urban areas are more vulnerable to disruptions.106 For example, energy and water systems are closely intertwined (Ch. 3: Water; Ch. 4: Energy; Ch.17: Complex Systems). Both higher water temperatures and extreme weather that causes power outages affect urban drinking water treatment and distribution. Higher air temperatures increase urban energy demand for cooling and water demand for landscaping. Elevated water temperatures affect cooling for electricity production. Higher river temperatures during periods of low flow can require power plants to shut down or curtail power generation to stay within defined regulatory temperature limits. Higher energy loads raise the risk of power outages. Flooding can drown electrical substations. Disruptions to water and power supplies can result in problems—such as unsafe drinking water, limited access to money systems, no functioning gas stations, few available modes of transportation, no air conditioning or heating, and limited ability to communicate with others—that pose risks to urban dwellers.
Climate change also threatens food security in urban areas.107,108 Loss of electricity from extreme weather leads to food spoilage. Transportation disruptions along the supply chain limit food mobility. Heat effects on agricultural labor impact product availability. Changes to the food supply generally lead to price volatility and food shortages, affecting household budgets and nutrition, cultural foodways, and food service profits. Urban populations who already experience food insecurity are likely to be affected the most.
Targeted coordination that addresses interconnected vulnerabilities can build urban resilience to climate change.109,110,111 Coordination may involve municipal offices, public–private partnerships, or state and local agencies. The Charleston Resilience Network, for example, brought together public safety and health services, business organizations, and the state transportation department to discuss their performance during the region’s October 2015 floods and to identify best practices to improve resilience.112
Cities across the United States are taking action in response to climate change for a number of reasons: recent extreme weather events, available financial resources, motivated leaders, and the goal of achieving co-benefits.113,114,115,116 One strategy being used is to mainstream adaptation and mitigation into land-use, hazard mitigation, development, and capital investment planning.45,115,117 Municipal departments from public works to transportation play roles, as do water and energy utilities, professional societies, school boards, libraries, businesses, emergency responders, museums, healthcare systems, philanthropies, faith-based organizations, nongovernmental organizations, and residents. City governments use a variety of policy mechanisms to achieve adaptation and mitigation goals. They adopt building codes, prioritize green purchasing, enact energy conservation measures, modify zoning, and buy out properties in floodplains. Nongovernmental stakeholders take action through voluntary protocols, rating systems, and public–private partnerships, among other strategies.
U.S. cities are at the forefront of reducing greenhouse gas (GHG) emissions (Ch. 29: Mitigation, KM 1). Urban mitigation actions include acquiring high-performance vehicle fleets and constructing energy efficient buildings. A number of cities are conducting GHG inventories to inform decisions and make commitments to reduce their emissions. Comprehensive urban carbon management involves decisions at many levels of governance.19
Many U.S. cities have also begun adaptation planning. A common approach is to enhance physical protection of urban assets from extreme weather. For example, protection against sea level rise and flooding can involve engineering (such as seawalls and pumps) and ecological solutions (such as wetlands and mangroves) (Ch. 8: Coastal, KM 2).118 Green infrastructure lowers flood risk by reducing impervious surfaces and improving storm water infiltration into the ground.72,119 Green roofs use rooftop vegetation to absorb rainfall. Urban drainage systems can be upgraded to handle increased runoff.72 Climate-resilient building and streetscape design reduces exposure to high temperatures through tree canopy cover and cool roofs with high albedo that reflect sunlight. Ensuring that critical urban infrastructure, such as drinking water systems, continues to provide services through floods or droughts involves a combination of technology, physical protection, and outreach (Ch. 3: Water, KM 3; Ch. 19: Southeast, KM 1).120,121,122
Social and institutional changes are central to urban responses to climate change (Figure 11.7).59,114 Urban development patterns reflect social, economic, and political inequities. As such, decisions about where to prioritize physical protections, install green infrastructure, locate cooling centers, or route public transportation have differential impacts on urban residents.60,123,124,125 If urban responses do not address social inequities and listen to the voices of vulnerable populations, they can inadvertently harm low-income and minority residents.60,123,124
Urban actions can reduce climate change impacts on cities.12,126,127,128,129,130 Urban adaptation plans often begin with small steps, such as improving emergency planning or requiring that development be set back from waterways (Ch. 28: Adaptation).59,131 Not all plans address weightier concerns, tradeoffs, behaviors, and values. For example, coastal cities at risk from sea level rise may be constructing storm surge protections, but not discussing the possibility of eventual relocation or retreat (Ch. 8: Coastal, KM 3).59,131 Increasing tree canopy and planting vegetation to manage storm water and provide cooling can increase water use, which may present difficulties for water-strapped cities.132,133
Urban adaptation and mitigation actions can provide near-term benefits to cities, including co-benefits to the local economy and quality of life (Ch. 29: Mitigation, KM 4).3,19,113,134,135,136,137 Tree canopies and greenways increase thermal comfort and improve storm water management. They also enhance air quality, recreational opportunities, and property values (Figure 11.8). Wetlands serve to buffer flooding and are also a source of biodiversity and ecosystem regulation.
Urban climate change responses are often constrained by funding, technical resources, existing social inequities, authority, and competing priorities.19,114,119,139,140,141 Coordinating among multiple jurisdictions and agencies is a challenge. Using scarce resources to address future risks is often a lower priority than tackling current problem areas. The absence of locally specific climate data and a standard methodology for estimating urban GHG emissions poses additional obstacles to urban responses.19,72,114 Cities are dependent on state and national policies to modify statewide building codes, manage across landscapes and watersheds, incentivize energy efficiency, and discourage development that puts people and property in harm’s way. Strong leadership and political will are central to addressing these challenges.59,131,142 Many U.S. cities participate in networks such as the U.S. Conference of Mayors, ICLEI, the C40 Cities Climate Leadership Group (C40), and 100 Resilient Cities. Others participate in regional coalitions such as the Southeast Florida Regional Climate Change Compact. Multicity networks support development of urban climate policies and peer-to-peer learning (Ch. 28: Adaptation).59,110,113,117,120,143 Effective urban planning to respond to climate change addresses social inequities and quality of life, uses participatory processes and risk management approaches, builds on local knowledge and values, encourages forward-looking investment, and coordinates across sectors and jurisdictions (Ch. 8: Coastal, KM 3).59,60,115,120,124,140,142,144
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.