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Adapting to Climate Sensitive Hazards through Architecture
Summary and Keywords
In architecture, mitigation reduces the magnitude of climate change by reducing demand for resources; anticipatory adaptation improves performance against hazards; and planned adaptation creates policies and codes to support adaptation.
Adaptation prepares for a future with intensifying climate conditions. The built environment must prepare for challenges that may be encountered during the service life of the building, and reduce human exposure to hazards. Structures are responsible for about 39% of the primary energy consumption worldwide and 24% of the greenhouse gas emissions, significantly contributing to the causes of climate change. Measures to reduce demand in the initial construction and over the life cycle of the building operation directly impact the climate.
Improving performance against hazards requires a suite of modifications to counter specific threats. Adaptation measures may address higher temperatures, extreme precipitation, stormwater flooding, sea-level rise, hurricanes, drought, soil subsidence, wildfires, extended pest ranges, and multiple hazards. Because resources to meet every threat are inadequate, actions with low costs now which offer high benefits under a range of predicted future climates become high-priority solutions.
Disaster risk is also reduced by aligning policies for planning and construction with anticipated hazards. Climate adaptation policies based on the local effects of climate change are a new tool to communicate risk and share resources. Building codes establish minimum standards for construction, so incorporating adaptation strategies into codes ensures that the resulting structures will survive a range of uncertain futures.
Keywords: adaptation, disaster risk reduction, armoring, flood-proofing, impact-resistant, resilience
The built environment provides the framework for human activity, but increasingly severe climate hazards are demanding changes to the way that cities are planned and buildings are constructed. In the period between 1995 and 2015, 90% of natural disasters were caused by weather-related events, including floods, storms, heat waves, and droughts, which affected 4.7 billion people who were killed, injured, made homeless, or required emergency assistance (CRED, 2015). Observed increases in the frequency, intensity, and complexity of extreme weather indicate an upward trend in weather-related disasters; at the same time, population growth and expanding settlements in floodplains and coastal zones increase human vulnerability to climate hazards. Adaptation requires the establishment and enforcement of building standards that are calibrated to meet climate hazards, improvements in building performance, and planning for integrated adaptation processes.
Disasters threaten economies through the potential for human costs, interruptions to productivity, and damage to buildings and infrastructure. The built environment represents 45–60% of nearly every nation's savings (Han & Ofori, 2001), and maintaining this resource is critical for economic stability. A disaster can wipe out years of development and investment in a single day, and divert a nation's resources from other priorities during the recovery period. Damage to the built environment influences a community's ability to retain existing businesses, attract new businesses, and encourage investment due to a lack of ready capacity in the commercial real estate sector, and damage to housing reduces the potential population. Buildings that withstand the effects of climate-sensitive hazards not only protect occupants but provide a platform for accelerated recovery.
Buildings are subject to a wide range of site-specific climate hazards, including: climatological (extreme temperatures, drought, wildfires), meteorological (hurricanes, precipitation and storms), and hydrological (floods, sea-level rise, and soil subsidence). Successful adaptation comprises multiple approaches that work together to transform the built environment: improving buildings and infrastructure so that they can withstand exposure to hazards, directing new development away from hazards, and maintaining the protective features of the natural environment. The following sections introduce the development of adaptation practices, outline measures to improve building performance, and describe planning for adaptation.
Box 1 Definitions
Adaptation: The process of adjustment to actual or expected climate and its effects. In human systems, adaptation seeks to moderate harm or exploit beneficial opportunities.
Adaptive management: A process of iteratively planning, implementing, and modifying strategies for managing resources in the face of uncertainty and change. Adaptive management involves adjusting approaches in response to observations of their effect and changes in the system brought on by resulting feedback effects and other variables.
Resilience: The capacity of a social-ecological system to cope with a hazardous event or disturbance, responding or reorganizing in ways that maintain its essential function, identity, and structure, while also maintaining the capacity for adaptation, learning, and transformation.
(Source: IPCC, 2014).
Development of Adaptation Practices
In primitive societies, buildings expressed an intimate relationship between people and their environment. Experience and innovation have widened the options for human shelters from the original cave or hut to the technically advanced structures of today, often supported by a reliance on technology to occupy otherwise unsuitable sites. As climate threats accelerate, adaptation practices are necessary to create awareness of the hazards and prepare structures to meet the new challenges. The following section explores the development of a formal system of human ecological planning, and the development of building codes and standards to protect the public health, safety, and welfare, and support adaptation.
Living with Nature
Humans are limited by the temperatures within which they can survive, and a narrower range in which they can live in comfort. When settlements were constructed by the people belonging to a particular locality, the structures relied on local traditions and place-specific knowledge that was refined and shared over generations. Buildings used materials that were available in the surrounding area, assembled in a manner that closely responded to prevailing weather patterns. Steeply pitched roofs of thatch, wood, or slate were built in areas with high precipitation from the snowy regions of Scandinavia to islands in the tropics. Flat roofs and thick walls made with mud bricks were constructed in arid places from the Arabian Sea to the American Southwest. Buildings responded in an intimate kinship with the site and the climate. The architect Frank Lloyd Wright described traditional architecture as "growing in response to actual needs, fitted into the environment by people who knew no better than to fit them with native feeling" (Wright, 2009, p. 116).
Prior to the industrial era, humans depended on the building envelope to create a suitable microclimate within which to dwell, and used the building form to modify the microclimate by creating a place to trap winter sun, protect against freezing blasts in winter, and shield openings from rain. People in hot climates used lightweight screens, wide setbacks from neighboring structures, with narrow footprints and rooms enfilade to encourage ventilation. In cold climates, they built thick walls of masonry and small windows to retain heat, and created building typologies with party walls to reduce the perimeter exposed to heat loss. Indigenous architectural form was modified through an extended period of experimentation to respond to local climate patterns.
Over the last century, building designers have constantly accommodated new technologies: electric light and appliances, mechanical systems, and communications equipment. Mechanical refrigeration and heating created a thermal environment that was independent of the temperature outside, extending human dominion over the interior climate. Eliminating combustion gases and open flames from the process of heating allowed buildings to become less permeable; air conditioning, introduced into residential use in the 1920s in the United States, also encouraged a tighter outer shell, and these mechanical advances had the effect of creating building envelopes with greater permanence (Banham, 1984). Building innovations were designed to accelerate productivity, enhance learning, increase leisure time, produce greater wealth, and extend the average human life span. Human social and economic activity became less dependent upon the climate, and people spent more of their lives within buildings, buildings which increasingly bore little connection to the local climate conditions or building traditions.
In the 1960s, architects, planners, and landscape architects began to reconsider the relationship between buildings and nature by examining the intrinsic qualities of the site. Design with Nature (1969) by Ian McHarg developed a methodology to integrate physical and biological sciences into design, establishing guidelines to analyze the aesthetic, natural resource, and social values of a site in order to determine the preferred location and pattern for human occupation. Richard Forman pioneered further advances in applied ecology through the use of LandSat imagery and geographic information systems in the 1980s and early 1990s, describing ecological networks that could be recognized as interconnected systems. His work in urban ecology explains how the constructed environment is spatially entwined with nature to form principles and patterns to improve urban areas for people and ecological systems (Forman, 2014).
Other designers and scientists examined biological networks as prototypes that could result in strong, durable, and resource-efficient structures. German architect Frei Otto worked with biologist J. G. Helmcke to study similarities between living and built structures, finding natural precedents from the molecular to the planetary scale and extrapolating design principles for lightweight long-span structures ("Natürliche Konstructionen," 1978). Stan Allen continues this line of inquiry, linking the operative and performative aspects of ecology with emerging design theory, describing how engineered systems may act as a physical scaffold for ecology (Allen & McQuade, 2011). In the same vein, architect William McDonough and chemist Michael Braungart examine resource cycles to identify new models for manufacturing buildings and products that challenge patterns of waste and consumption, and transform the components into either biological or technical nutrients (McDonough & Braungart, 2002).
Living with nature often means living with water. New Orleans gained attention as the new frontier of water management following Hurricane Katrina. Historic approaches to "living with water" really meant removing stormwater as quickly as possible. The Greater New Orleans Urban Water Plan (Waggonner & Ball Architects, 2013) addresses flooding caused by rainfall of over 60 inches per year, subsidence caused by pumping stormwater out of the city, and wasted water assets (see Figure 1). Proposed water gardens and greenways for water storage and filtration are ringed with public access and recreation areas. The plan is designed to accommodate increased rainfall and sea-level rise in this city, located at the mouth of the largest river delta in North America.
Examining the structure of nature encourages an understanding of the complexities underlying place, incorporates natural processes in building materials and services, and develops formal design principles in place of the vernacular. For architects and engineers, trained to see the environment as a resource to be consumed, the understanding that buildings could work in harmony with nature represents a shift in design thinking (Fischer & Hajer, 1999). Living with nature, instead of attempting to subdue the environment, requires that individual projects are understood as part of a larger system, one which no longer isolates a building as the sole defence against the climate for its occupants, but incorporates a network of land-use decisions, infrastructure, and landscape features.
Building Regulations to Support Adaptation
Buildings within the cities of highly developed nations are typically designed to meet a variety of regulatory codes, local ordinances, and standards which control the performance requirements of building materials. There are several types of standards that can incorporate adaptation:
• Building codes establish the minimum requirements for human occupancy;
• Enhanced codes outline requirements for high performance in essential facilities, so that they may continue to operate in severe conditions;
• Land-use ordinances define acceptable development patterns;
• Sustainability rating systems outline strategies for efficient resource use and environmental quality.
These codes and guidelines respond to changing demands for safety and responsibility through an iterative process based on comments, concerns, and failures observed in the implementation of previous codes. They have historically addressed climate hazards directly through regulating fire protection, energy efficiency, wind resistance, and flood resistance. Codes are updated on a regular schedule, such as the International Building Code's three-year cycle, ensuring that the standards are current and relevant. As buildings are renovated or replaced, compliance with the adopted code is mandatory; even though building codes affect less than 1% of buildings each year (Shaw, Colley, & Connell, 2007), as the code is applied over a period of years, an increasing percentage of the built environment becomes compliant with the standards.
Disasters are often the inspiration for modifications to building codes. Damage from Hurricane Andrew in 1992 spurred the state of Florida to adopt higher performance measures to address wind-borne debris, wind uplift, and lateral resistance. When implemented, the code improvements were proven to reduce losses: a study after Hurricane Charley in 2004 showed that homes built before the new codes were adopted in 1996 suffered an average loss of $24 per square foot, whereas houses built after 1996 had an average loss of $14 per square foot (IBHS, 2007).
Enhanced standards for performance are used to protect essential structures against severe weather, including tornados and hurricanes. The Federal Emergency Management Agency's Tornado Protection created initial guidelines for wind resistance in 1976, and the agency continues to refine the principles based on post-damage assessments. Compliance with the current edition of Safe Rooms for Tornadoes and Hurricanes provides "near-absolute protection from wind and wind-borne debris" (FEMA, 2015, p. i). A requirement for continuity of operations in hospitals, schools, nursing homes, first-responder facilities, and community shelters ensures that essential systems (power, communications, water, and wastewater) remain functional throughout the storm.
Land-use ordinances determine the density of occupation, and the relationships between functions, such as separating industrial zones and residential areas. Many of the fatalities that occur as a result of natural hazards are concentrated in rapidly urbanizing centers without land-use guidelines. Informal settlements may be located within areas that are unsuitable for permanent occupation; floodplains, steep slopes, or contaminated lands may be the only lands remaining for expansion because the sites are compromised and the least valuable for development. Land-use plans often determine the scope and location of new infrastructure. Insufficient infrastructure may increase vulnerability: roads may be too narrow for emergency vehicles or evacuation; water supplies may be intermittent, distant, or too unreliable to provide water during droughts or fires; wastewater may discharge into water bodies that provide drinking water of food sources. Improving land use planning to meet climate-sensitive hazards will be discussed in "Planning for Adaptation."
Sustainability rating systems reduce the resources used in the construction and operation of buildings, savings which mitigate climate change. Voluntary "green" certification programs are designed to improve occupant health, lower operational costs, improve productivity, and increase the market value of rated buildings. Rating systems have a positive effect on curbing energy consumption by improving the building envelope, which mitigates higher temperatures, a climate-sensitive hazard. Water conservation addresses drought conditions by reducing potable water use. Sustainable site initiatives address flood hazards by expanding stormwater capacity onsite.
Efforts to mandate sustainability have met with mixed success. The European Union Directive on Energy Performance of Buildings requires reducing energy use by 20% from a 2007 baseline (European Parliament, 2010), and the EU is studying a common framework of indicators for the environmental performance of buildings. The United States requires federal buildings to reduce greenhouse gas emissions by at least 40% by 2025.
Box 2 Mitigating Climate Change through the Built Environment
The consumption of fossil fuels has a spiralling impact on the environment; burning fossil fuels has changed the global climate, increasing average temperatures, and resulting in higher demands for energy to maintain the same level of comfort within buildings. Structures consume about 39% of the primary energy worldwide and produce 24% of the greenhouse gas emissions (International Energy Agency, 2014). The building sector is responsible for the largest share of energy use, exceeding the industry and transportation sectors.
The built environment may mitigate the effects of climate change in several ways: reducing the size of dwellings to use fewer resources to construct, operate, and maintain; increasing density to minimize transportation between home, workplace, and services; using locally harvested, manufactured, or recycled materials to reduce the embodied energy in construction materials; engaging occupants to meet efficiency goals; shifting to renewable energy sources and limiting consumption of fossil fuels; and building to meet the specific climate and site conditions.
The International Union of Architects World Congress in 2014 unanimously pledged to eliminate CO2 emissions in the built environment by 2050. "Net-zero" buildings are carbon neutral when measured on an annual basis, which allows a balance between consuming and generating energy. The following definitions are included in U.S. president Barack Obama's Executive Order: Planning for Federal Sustainability in the Next Decade (White House, 2015):
Sustainability rating systems are consensus-based organizations, focused on resource-efficient buildings and sites. Voluntary certification programs have been developed worldwide, including: Building Research Establishment Environmental Assessment Methodology (BREEAM) beginning in 1990, U.S. Green Building Council (USGBC) in 1993, Architecture 2030 Challenge (2002), and the Living Building Challenge (2006). Most certification programmes offer a range of options with varying levels of green compliance; USGBC's LEED rating levels are Certified, Silver, Gold, and Platinum.
Low-carbon cities approach carbon neutrality at a larger scale. The International Council of Local Environmental Initiatives (ICLEI) supports over 1,200 cities, towns, and counties as they pursue low-emission development standards: emission measuring and inventories, energy-efficient street lighting, integrated waste-management planning, afforestation, replacing individual vehicles with shared transit, bike sharing programs, green buildings, and regional land use development frameworks. In addition, ICLEI supports the expansion of renewable energy supplies to meet the goal of producing 100% of energy from renewable sources by 2030.
Many cities are defining low-carbon zones to test energy efficiency and carbon reduction measures. London funded pilot projects in ten boroughs, modifying over 4,000 homes (performing energy audits, draft-proofing, insulation, retrofitting, and installing solar photovoltaic and solar thermal systems), and civic and commercial structures (installing solar systems, retrofitting equipment, and energy modeling software), as well as transport, food, water, waste, and communications initiatives. Among the pilot projects, the most effective measures to reduce CO2 emissions were retrofits at large, public buildings and social housing, which installed larger-impact, higher-cost measures such as efficient boilers and heat-recovery systems. In private households, the individual energy assessments led to customized solutions, and the face-to-face engagement with occupants inspired changes in behavior (Centre for Sustainable Energy, 2014).
(See the Oxford Research Encyclopedia of Climate Change Communication).
The International Green Construction Code (IGCC) was launched in 2012 to quantify a standard for the impact of buildings on the environment, but adoption has been limited in the United States: Florida requires the IGCC for state-owned facilities, and it has been adopted as a voluntary standard for energy performance in Oregon, Rhode Island, and Maryland.
The adoption and enforcement of building codes recognize the role that oversight plays in health, safety, and welfare. Cities which do not adopt and enforce codes assign the responsibility for public safety to architects, who may have limited administration of the contract for construction; to contractors, who may have a limited period of liability; or to owners, who may not be aware of safety regulations. The resulting structure may be low-quality construction which provides adequate stability under normal conditions, but fails when subjected to climate hazards.
Improving Building Performance against Climate Hazards
Adaptation is the process of incremental alignment to meet current and anticipated climate conditions. The term "global warming" singles out only one of the hazards projected to increase as a result of climate change—higher temperatures—but there are other climate threats against the built environment: climatological hazards including extreme high temperatures, drought, and wildfire; meteorological hazards including hurricanes, intense precipitation, and storm surge; and hydrological hazards such as flooding, sea-level rise, and soil subsidence. Improving building performance against hazards and guiding development to sites with a reduced potential for hazards reduce human exposure to risk. Without adaptation, a structure's purpose, operations, and longevity may be compromised. The following sections describe threats to the built environment, and outline adaptation measures to reduce impacts on buildings and occupants.
Climatological: Temperature
The ten hottest years on record have all occurred since 1998. The Intergovernmental Panel on Climate Change (IPCC) forecasts a rise in global mean temperatures of 1.5 to 4.7 degrees Celsius (2.7–8.5 degrees Fahrenheit) over the remaining years of the 21st century (IPCC, 2014; the wide range of possible consequences is the result of the uncertainty of potential mitigation actions and different emissions projections). As the temperature climbs, human exposure to extreme heat is also rising, calculated by multiplying the number of days over 35 degrees Celsius (95 degrees Fahrenheit) by the number of people in the area; in 2000, the average annual exposure to extreme heat in the United States was about 2.3 million person-days, but by 2050, that number could quadruple (Jones et al., 2015).
Humans require a relatively constant body temperature for comfort; high temperatures and high humidity compromises normal human activity. Within limits, the body can adjust to thermal changes such as the slow, seasonal shift from summer to winter, as well as abrupt transitions between indoors and outdoors. Thermal comfort zones inside a building are outlined in the American Society of Heating, Refrigerating, and Air-Conditioning Engineers Standard 55 (ASHRAE, 2013), Thermal Environmental Conditions for Human Occupancy. They identify the comfortable temperature range on a psychrometric chart indicating the operative temperatures and humidity at which thermal comfort is achieved. Variables include: ambient temperature, or air temperature; radiant temperature, of surfaces around occupants; relative humidity, the measure of water vapor in the air; air motion, the rate at which air moves around and touches skin; metabolic rate, the amount of energy expended; and clothing insulation, the materials which retain or remove body heat. It is useful to remember that higher-temperature weather is often accompanied by increased precipitation because warm air holds more moisture than cool air, resulting in both hotter and more humid climates.
Many buildings depend on mechanical equipment to reach the desired thermal comfort for occupancy, but these systems are resource-intensive to furnish and operate. In both warm and cool climates, appropriate orientation of the building, a higher-performance building envelope, and high-efficiency equipment can provide greater human comfort and reduce the emissions which contribute to climate change. This is especially critical in a warming climate, because mechanical equipment requires more energy to cool (the sensible cooling load) than to heat a space. In addition, removing moisture (the latent cooling load) uses more energy than dry cooling loads, causing peak demands for power on hot, humid days.
Passive cooling using nonmechanical strategies helps equipment work more efficiently, manipulating orientation and shading to provide solar control. Orienting the long edge of a building along the east-west axis and providing roof overhangs on the elevation facing the sun reduces direct sun in summer, and invites warmth in winter. Vertical fins on east and west facades shade windows against the low angle of the sun's altitude in the early morning and late afternoon. Awnings, fins, louvers, and brise-soleils can be projected from the façade in fixed or movable configurations, made with opaque or screened materials, or driven by thermally coupled sensors, thus reducing sunlight from the exterior in summer, and allowing direct heat gain in winter.
A high-performance building envelope can reduce the size of heating and cooling equipment by limiting thermal transfer from the outside. One characteristic of a high-performance envelope is reduced air infiltration; normally there are hundreds of penetrations in a building, and sealing the gaps with house wrap, sealants, foam, and adhesive flashing can improve energy efficiency by 25% or more. The second function of insulation is resisting heat flow; low-density materials such as fiberglass, foamed polyurethane, cellulose, or mineral wool add thermal resistance (R-value) for each inch of material thickness, ranging in efficiency from about 2.2 for fiberglass to 6.25 for foamed polyurethane (a higher R-value indicates greater resistance and better performance).
Windows have a significant impact on the building envelope, as they are traditionally the elements that are most susceptible to solar heat gain. Windows with a lower Solar Heat Gain Coefficient (SHGC) transmit less solar radiation through the glass; glass coatings provide built-in shading by reflecting the long-wave, infrared radiation and emitting only a small percentage of that heat energy to the interior. Windows may also use insulating glass assemblies to reduce thermal transfer, with air or other gases in the space between double or triple panes.
Humans get relief from high temperatures by the evaporation of moisture from the skin. Opening windows on opposite sides of a building supplies fresh air and permits cross-ventilation airflow. Natural ventilation strategies can be effective if there are limited interior partitions or obstructions and a narrow floor plate, about 45 feet wide, to distribute air throughout the area. Placing windows so that they are staggered, and not directly in line with each other, promotes air mixing within the space.
Building innovations encourage natural ventilation in large structures using double-skin façades with a naturally or mechanically ventilated air space between planes. The physics of buoyancy allow buildings to draw in cool air from low openings or through underground piping, and the stack effect creates an updraft by the air, which rises as it heats, exhausting at the top. Windows in both layers of a double-skin façade may open to allow fresh air intake and exhaust, or close to preheat air in winter. Natural ventilation works within a range of temperatures, but there is a limit to the effectiveness of natural ventilation in hot, humid climates, as moist air inhibits the ability of a body to perspire and cool off. A mixed-mode system uses natural ventilation when temperatures are close to the human comfort range and relies on mechanical ventilation in other seasons, reducing the annual energy consumption by 10–30% without affecting human comfort.
More periods of extreme heat, and higher mean temperatures overall, demand better heating, ventilating and air conditioning (HVAC) equipment. Manufacturers are developing a variety of alternatives to supply human comfort while reducing energy use: high-SEER units; variable-air-volume systems and low-flow diffusers to perform at part-load conditions instead of continually cycling on and off; radiant floors and chilled beams, convection systems which induce air circulation across the occupied zone; ductless systems with the flexibility to set individual temperature controls; heat recovery systems which introduce fresh air through a heat-exchange component; desiccant wheels to reduce humidity; and ground-source heat exchanges, which use piping looped through the soil to preheat or precool intake air, using the stable temperature of the earth as a heat sink in summer or heat source in winter. These formerly novel techniques are becoming mainstream as the population moves to warmer areas, demanding greater energy efficiency.
The cumulative impact of energy use may overwhelm power grids on hot summer afternoons, when air conditioning loads are high, workplaces are running electronics and lighting, and industrial production is underway. Electricity infrastructure is insufficient to meet projected energy demands, and service disruptions are anticipated to become more widespread (ASCE, 2013), and consumers may experience brownouts during periods of peak power use in extreme heat waves unless energy conservation measures are applied. Communities that are unprepared for extended periods of hot weather may experience casualties, electricity brownouts, and interruptions to public services.
Conservation measures include dimming the lights in noncritical spaces such as lobbies and corridors of large commercial and industrial buildings, or deferring the use of certain industrial equipment until evening hours, when power is cheaper. Individual consumers can allow "smart grid" thermostats to raise the setpoint 2 degrees hotter, reducing air conditioning use temporarily in return for cost savings. These types of automated building controls reduce "peak loads" and the possibility of grid failure.
In order to ensure continuous power, buildings may integrate renewable energy generation onsite. Solar energy, solar thermal water heating, and building-mounted wind turbines are approaching grid parity, or the cost of supplying electricity from the grid. In conjunction with improvements in battery storage, onsite generation offers a reliable source of power, and a reliable way to meet higher temperatures, storms, and other climate-sensitive hazards.
In addition to buildings, the urban form may be designed to mitigate high temperatures. Masdar City in the United Arab Emirates links high-efficiency mechanical design with passive techniques to provide human comfort in the desert, where average high temperatures in July and August reach 42 degrees Celsius (108 degrees Fahrenheit). Foster + Partners planned narrow streets to reduce direct sunlight and buildings with articulated facades to increase turbulence and produce air movement; together, these strategies lower the temperature at street level between 15 and 20 degrees Celsius (59–68 degrees Fahrenheit; Kingsley, 2013). The high thermal mass of the buildings delays the effect of solar radiation, reradiating heat at night when the air temperature is cooler. The extreme heat of the surrounding desert encourages human tolerance for a wider temperature range, and the sequence of transitional spaces acclimates people gradually to increasing levels of comfort: from open desert to shaded streets, into corridors with limited air conditioning, to a fully controllable interior space. Masdar City is powered by a concentrated field of more than 85,000 solar panels producing 10 megawatts of electricity, with solar panels on building roofs adding 1 megawatt.
Treasure Island, or Yerba Buena Island, is located in San Francisco Bay, at the site of the 1939 Golden Gate International Exposition. Redevelopment of the site for mixed commercial and housing rotates the street grid 68 degrees to promote sunlight at parks, streets, and buildings, and protect pedestrians from prevailing westerly winds (see Figure 3). The 8,000 new housing units contribute to lower energy use through building envelopes incorporating shading, daylighting, and natural ventilation. The urban plan calls for 1 million square feet of solar photovoltaic panels, a central plant with a distributed heating and cooling system, and a cogeneration system to provide electricity from organic waste, measures which improve energy efficiency.
The Chicago heat wave in July 1995 resulted in 739 deaths in five days; most of the victims were poor, elderly residents who could not afford air conditioning and were reluctant to open their windows or sleep outside because of their fear of crime. The victims' isolation played a key role in the high mortality as they had limited access to information and a reduced capacity to mobilize resources at a dangerous time (Klinenberg, 2002). Increasing density and greater stratification of social groups has a negative impact on social connection, although the spatial order of the city may provide some relief by providing the connective infrastructure that links people together. Sidewalks, parks, gathering spaces, libraries, and community centres create places for the elderly and disadvantaged to find comfort when weather conditions deteriorate.
Cities designed to lower temperature impacts may conflict with the established urban form. Narrow streets reduce heat gain, but they also limit vehicular traffic. Buildings with natural ventilation require narrow floor plates, operable windows, and space around them for access to airflow, which may affect urban density. Increased shading requires louvers, screens, and overhangs that affect traditional building setbacks and facades. Solutions to improve human comfort, provide energy efficiency, and work within the dense, urban context must balance these constraints.
Climatological: Drought
The land area subject to degradation from desertification and drought has increased from 15% in 1991 to 25% in 2011, encompassing locations outside of traditional deserts (UNCCD Secretariat, 2013). As human populations increase in arid regions, demand for water will exceed the supply available in reservoirs and aquifers. Water shortages already affect populations through insufficient water service, wells running dry, and the subsequent agricultural effects.
Inappropriate land policies lead to land degradation: the location of agricultural lands in areas unsuited to their water needs; deforestation of land for development; and removing vegetative cover, which increases water runoff. In the urban environment, the impervious ground plane and channelized drainage reduces the catchment areas, which would otherwise recharge groundwater supplies. There are two ways the built environment can address drought: through water conservation and the restoration of water catchment systems.
Water conservation offers an alternative to extracting and treating new water supplies. A powerful tool to reserve potable water for human use is to conserve water in urban landscapes; in California, about half of the water use in cities is dedicated to landscape irrigation. Governor Jerry Brown issued an executive order in 2015 proclaiming a state of emergency due to severe drought and requiring a 25% reduction in potable water use in urban areas. The plan included replacing 50 million square feet of ornamental lawns with drought-tolerant landscape, reducing water use at commercial, industrial, and institutional landscapes, a prohibition on new spray irrigation systems, replacing inefficient plumbing fixtures with water-saving versions, and developing new rate structures to maximize water conservation. The order also provided assistance to move people from housing units which had lost access to potable water because private wells were dry. Results from June 2015 to March 2016 when the program ended showed a cumulative 23.9% savings, just shy of the target reductions (California State Water Resources Control Board, 2016).
Domestic consumption is less than 15% of the global demand for water. Average use in developed countries is 500–800 litres per person, per day (UNEP, 2008). Water used to flush toilets accounts for about 30% of the indoor water use, but toilets don't require potable water for flushing; recycled gray water, the waste water from showers, lavatory sinks, tubs, boiler or chillers, and washing machines may be used instead. (Black water, the effluent from toilets and kitchen sinks, is not reused due to the potential for contamination.) Gray water reuse systems include a filter to eliminate dirt and soap residue, a tank for gray water storage, a flow control valve so that excess water is diverted to the sewer, and piping from the storage tank to the toilet.
Where municipal water supplies are irregular, insufficient, or expensive, rainwater catchment may be necessary. In Bermuda, the island's geologic base is limestone, and wells supply brackish water which is only used to flush toilets. A typical island house has a stepped roof profile to slow rainwater, with a white coating to reflect heat and disinfect surfaces. Each house has an average rooftop catchment area of 1,500 square feet and a storage tank capacity of 15,000 gallons to provide residents with potable water during the dry season from January to April (Bermuda Department of Public Health, 1989).
In countries with developing infrastructure, municipal supplies may experience interruptions, making household water storage necessary. Delhi, India, delivers water through the municipal pipes for only 60 to 90 minutes each day, and to only about half of the city's 20 million residents. Many residents installed water storage tanks to ensure a reliable water supply, but in 2001, India began a program to require rainwater collection systems on new buildings with a roof area greater than 100 square meters (ICPWD, 2002). The catchment system fills the building water tanks, and the excess is used to recharge the city's aquifers.
Collecting rainwater for public use is not a new idea in India. The region has been inhabited since the 6th century bce, and it has experienced prolonged periods of drought. Stepwells carved from the earth allowed community access to fresh water supplies (see Figure 4). A stair or ramp descends to the fluctuating waterline; water levels rise when swollen with rains, and retreat in advance of the monsoon. Many of these community reservoirs still function today.
Rainwater harvest is threatened by water rights in some areas where water supplies are limited, notably in the western United States. The legal justification for blocking property owners from harvesting rainwater on their own land is the concept of prior appropriation; early settlers claimed water rights, maintaining them through generations as long as the water is used for beneficial purposes, including mining, industrial, agricultural, or household uses. Rain upon the rooftops will ultimately find its way to rivers if not intercepted, and thus by law, water must flow unimpeded into the streambed. Rain barrels and cisterns are considered impediments to stream replenishment, even if only 3–15% of rainwater returns to the stream system (Colorado Water Conservation Board, 2007). These laws are being challenged in states experiencing severe droughts.
Climatological: Wildfire
When drought is coupled with higher temperatures, the risk of wildfire increases, and the duration of individual fires and the fire season are prolonged. Fires have tremendous negative impacts on human health, the economy, and the environment. Risks to the built environment include direct fire damage to infrastructure and properties, as well as collateral damage from land degradation and flooding from the loss of vegetative cover.
Throughout history, fire has posed a significant threat to buildings and occupants. Over 40% of fires start within structures, as a result of faulty electrical circuits, appliances, cooking, portable heaters, seasonal decorations, and smoking-related ignition. Extending settlements from urban areas into wildlands increases human vulnerability to fires that start as a result of natural ignition.
Fire's potential for contagion inspired building codes for fire-resistive materials as early as 1666, after the Great Fire of London; standards now also include fire notifications, suppression systems, and adequate means of egress from buildings. Fire-rated assemblies delay combustion rates, allowing occupants the time to escape, and firefighters to arrive. Fire-resistive materials include exterior finishes at the roofs (asphalt, concrete, clay tile, slate, and metal) and wall cladding (fiber-reinforced concrete board, metal, and treated wood). Interior finishes are classified according to the rate of flamespread and smoke developed when they are exposed to an open flame.
At the sub-urban interface, buildings may become new sources of combustion for fire hazards, and people may provide the spark; electrical transmission lines to serve buildings near wooded areas pose an additional ignition risk from electrical faults or overturned power poles.
Property owners in fire-risk zones can prepare by restricting the tree canopy within 30 feet of a structure, and planting only vegetation with low combustibility. These firebreaks create a fuelless barrier, but fire can jump wide gaps; in southern California, Santa Ana winds can blow embers across an eight-lane freeway. When wildfires intersect with highways, they may restrict evacuation, as they did in the Fort McMurray fires in Alberta, Canada, in 2016. Police escorted escape convoys, 50 vehicles at a time, evacuating 7,500 people, but many vehicles were prevented from going south by the fire and were diverted, requiring airlifts out of isolated areas. One solution to prevent isolation is to ensure multiple evacuation routes out of communities at the wildland interface.
Australia has experienced an increase in heat waves and drought conditions, accompanied by devastating bushfires. The Simpson-Lee house, designed by architect Glenn Murcutt, has a corrugated metal shed roof to collect rainwater, funnelling it into cisterns with a combined capacity of 35,000 litres (Figure 5). The cisterns feed an automatic rooftop sprinkler system to wet the outside of the house when fire threatens the property. Building materials are ignition-resistant corrugated steel, aluminium, glass, and concrete. An open reservoir between the two volumes of the house is filled with water to act as a firebreak. The building is sited on a rock outcrop, but it has a narrow perimeter to the eucalyptus forest in order to maintain shade and sensory pleasure from the trees; the conflict between clearing the site and providing safety is an example of the sensitive balance that designers navigate when the capacity of natural systems is under stress.
Meteorological: Hurricanes
Hurricanes pose a triple threat to the built environment: high winds, intense rainfall, and storm surge. Oceans have absorbed about 20 times more heat than the atmosphere in the past fifty years, resulting in higher surface temperatures. This will likely cause hurricanes to be more intense on average, with an increase in the occurrence of very intense storms, with 10–15% higher rainfall rates (GFDL, 2016).
Hurricane wind forces damage a structure in three ways: through differential pressures on the building envelope, wind-borne debris, and collateral damage, when an adjacent tree or structure falls on a building. Differential pressure is caused by wind at high speeds creating positive pressure on the windward wall, and negative pressure, or suction, on the leeward wall and roof. The combination of positive and negative forces can cause uplift (lifting the edge of the roof or sheathing), sliding (displacement off the foundation), overturning (rotation off the foundation), and/or racking (the structural frame tilts or collapses). Protecting a structure against wind damage requires providing a continuous load path for the structure to resist uplift, sliding, overturning, and racking, and deflecting wind-borne debris. A continuous load path is established with high tensile strength connections between the walls, floors, roof, and foundation. A breach in the building envelope allows wind to enter the building: if a breach is on the windward wall, positive pressure forces the walls and roof outward; if a breach occurs on the sides or leeward wall, the internal pressure is reduced and the walls and roof are pulled inward.
When a structure fails in a hurricane, loose pieces become wind-borne missiles, propelled at high velocity to threaten neighboring structures. Brittle materials, such as glass, normally cannot absorb the force of a missile strike, but impact-resistant glazing resists breakage due to a plastic interlayer which supports the glass as it flexes. Impact resistance is determined in laboratory tests, using steel ball bearings as small missiles peppered at the window at 88+ miles per hour (130 feet per second); or 2x4 wood studs for large missiles, propelled at speeds up to 100 miles per hour (147 feet per second). Impact resistance ranges from the "Miami-Dade" standard (a 9-lb. 2x4 at 34 mph, equal to 348 ft.-lbs. of pressure) to the tornadic standard (a 15-lb. 2x4 at 100 miles per hour, equal to 5017 ft.-lbs. of pressure) (FEMA, 2015).
Following Hurricane Katrina, a group of community evacuation shelters were constructed in Mississippi, well outside of the 500-year floodplain. They were designed with curved walls and a parabolic roof to direct wind over and around the building, and aerodynamic detailing and minimal overhangs reduced the surface area susceptible to uplift (Figure 6). Parametric modelling of the self-stabilizing form allowed the structural steel to be reduced by as much as 20% (Anderson, Anderson, & Herrin, 2011). Concrete walls were reinforced with earth berms to absorb impact from windborne debris. At the most exposed plane, the roof's 6-inch concrete slab resists collateral damage from falling debris, and is covered with a liquid-applied membrane instead of a mechanically fastened waterproofing layer, which might be damaged in high winds. Every roof penetration, including air intakes, exhaust fans, roof hatches, and other building-mounted equipment, is armored.
Hurricane-prone areas of the globe have a long history of adapting architecture to meet high winds and flooding, as well as meeting the cultural mores of the area. Bangladesh leads the world in fatalities from cyclones, and a coordinated response became a national priority after 140,000 people were killed in Cyclone 2B in 1991. The country has significantly reduced cyclone-related deaths by constructing over 4,000 reinforced concrete cyclone shelters and government offices that can be used as shelters (Figure 7), in addition to modernizing early warning systems, constructing coastal embankments, and enhancing coastal forests (Haque et al., 2012). Even with these improvements, government analysis determined that an additional 7,124 shelters are needed by 2025 to protect the population at risk in 14 coastal districts (World Bank, 2014).
The structures are constructed on plinths elevated above the floodplain, with a platform for livestock, an essential component of recovery in this agrarian nation. In deference to religious practices in this predominantly Muslim country, many of the shelters have separate quarters for men and women. However, many of the shelters have features that contribute to an unwillingness to use them during a hurricane: located far from houses, with minimal oversight that permits overcrowding or poses dangers to women, a lack of toilets, or poor maintenance. The shelters that were built as single-use structures, only used to aid disaster victims, deteriorated as a result of the moist, tropical climate, a condition which also plagued the Mississippi shelters. Future shelters in Bangladesh will be planned with multiple functions, including schools, community centers, and offices.
Cyclone-proof homes are being tested by the Housing and Building Research Institute in Dhaka, with concrete foundations, walls, and roofs that are capable of withstanding 130 mph winds. In the United States, residential structures may be "fortified," a designation by the Institute for Business and Home Safety, by strengthening the structure at the roof sheathing and fastening, providing a sealed deck, and reinforcing the soffits, attic vents, gable ends, and porch roofs; these improvements have been tested to failure at about 100 mph (IBHS, 2007). Improvements such as these enhance safety when sheltering in place, if evacuating to a community shelter is not possible.
Meteorological: Precipitation and Storms
Climate models show substantive changes in rainfall patterns by the late 21st century, with heavy precipitation events very likely to increase in frequency, intensity, and/or the amount of rainfall over most of the mid-latitude land masses and wet tropical regions (IPCC, 2014). Intense rainfall is likely to cause building failures and flooding in areas that are unprepared to cope with large quantities of water. Adaptation measures create building forms which direct water away from openings, and building envelopes that are watertight.
The roof is the building plane with the greatest exposure to precipitation. Low-slope roofs (one-quarter inch per foot to 4 inches per foot), folded-plate, and butterfly roofs depend on advanced materials to improve waterproofing membranes: single-ply membrane roofing with a prefabricated thermoplastic or thermoset polymer sheet; and modified bitumen roofing of asphalt with a polymer added for its elastic properties, and fabric reinforcement for strength. An ice and water shield of self-adhering, rubberized asphalt may be added beneath shingle or metal roofs for a redundant layer of waterproofing, providing a belts-and-suspenders approach to guard against leaks (Figure 8).
Vegetated roofs are another way to manage precipitation. There are two types of green roofs: extensive, with 5 to 8 inches of growth medium to support groundcover, herbs, and shrubs; and intensive, with soil depths of up to 3 feet for tree planting. Vegetated roof assemblies include multiple layers: structural deck, waterproofing membrane, protection board, root barrier, drainage mat, filter sheet, lightweight structural soil, and plants. Because the weight of a water-saturated vegetated roof is equivalent to the weight of a pool of water, the structure beneath must be sturdy enough to support the additional weight. This assembly has an added benefit in coastal zones, as the extra weight of the roof may act as an anchor against storm surge and other lateral forces.
The roof is not the only building plane subject to water penetration. Wall cladding may present the appearance of a waterproof layer, but it does not always form a barrier to moisture. Moisture condenses from warm, humid air when it moves to a place that is colder than the dew point. Vapor retarders, placed on the warm side of an assembly, reduce condensation on cooler building elements such as the structural frame, insulation, interior finishes, and conditioned spaces (Lstiburek, 2011).
Windows and doors provide multiple opportunities for water or vapor to enter a building. Because they are operable, are composed of many parts, and use brittle materials, openings are vulnerable points in the building envelope. Covering openings with overhangs, awnings, arcades, or extended drip edges can protect against rainwater. Flashing at windows and doors is designed to prevent water intrusion from wind-driven rain and to waterproof the seams between different planes or materials. Door thresholds are particularly susceptible to water; accessibility demands they remain nearly level with the floor, instead of the high, bulkhead type found on ships. Thresholds with neoprene gaskets, which are compressed when the door is closed, prevent water from seeping under the threshold. Outswing doors are preferred to keep water out, as the wind pressure pushes against the door and compresses the weather stripping, making it more water-resistant.
Intense rainfall can saturate the ground next to the building and cause surface water buildup against foundation walls or thresholds. Sloping the grade away from the perimeter, and installing an impermeable layer such as clay or concrete on the surface, directs groundwater away from basements and foundations. A vapor retardant membrane beneath the slab, waterproofing at the exterior of basement walls, and a vapor impermeable layer at the interior face of a basement wall keeps groundwater from being drawn into the drier space of the building. Gravel substrate and backfill around foundation walls and below slabs work as a capillary break to reduce the potential for moisture to migrate through the foundation; these areas should be vented to the outside so that vapor can bypass the conditioned space (Lstiburek, 2006). Because foundation materials are often made with porous masonry and concrete, a horizontal barrier can arrest the potential capillary action between foundations and exterior walls; a damp-proof course is recommended to prevent moisture from traveling up the wall and causing deterioration.
Maintaining a watertight building envelope requires vapor transmission barriers at every surface of the building: roof, walls, openings, and below grade. In contrast, high-rainfall tropical climates often used a breathable envelope of low-mass materials such as thatch, bamboo, and slats to avoid condensation and prevent mold growth. This approach allows buildings to capitalize on natural ventilation between rainfall events to fry out the materials and spaces. Traditional breathable skins may not meet modern expectations for thermal comfort and rain protection, but their occupants balanced the atmospheric conditions through operable panels, doors, and windows. This traditional way of building is leading materials scientists to develop dynamic building skins of metal skeins or polymer scales which are designed to resist moisture and dry quickly.
Hydrological: Flooding, Storm Surge, and Sea-Level Rise
Flooding is the most common environmental hazard worldwide, causing deaths and property damage, and disrupting emergency services, economic systems, food production, and utilities. The concentration of human population in flood-risk zones exacerbates the problems in coastal and riverine ecosystems. The population within the 1-in-100-year coastal flood hazard area is projected to increase from about 270 million in 2010 to 350 million in 2050. "Without adaptation, hundreds of millions of people will be affected by coastal flooding and will be displaced due to land loss by year 2100" (IPCC, 2014, p. 364). This section will examine architectural responses to two types of flooding: coastal flooding from high tides, sea-level rise, and storm surge; and surface water flooding from intense precipitation.
Coastal flooding is increasing as a result of several climate factors, including sea-level rise, soil subsidence, and hurricanes, but is also due to human factors, placing the built environment at risk by constructing a nearly continuous impermeable ground plane, rebuilding structures that have experienced repetitive flooding, and reducing vegetative cover. Global sea level is projected to rise during the 21st century, with scenarios of 0.22 to 0.44 meters above 1990 levels by the mid-2090s (IPCC, 2012). Storms push ocean waters inland to form storm surge on top of sea levels and tides. Nuisance flooding as a result of climate-related sea-level rise, land subsidence, and the loss of natural barriers inundates roads, isolates communities, and damages infrastructure. As the list of assets in floodplains grows, losses from flooding in the world's coastal port cities could near $1 trillion annually by 2050 (Hallegatte, Green, Nicholls, & Corfee-Morlot, 2013).
Surface water flooding occurs when rainfall exceeds the evaporation rate plus the infiltration capacity of the ground. Impervious surfaces, such as roads and roofs, reduce the infiltration capacity. The impact of flooding is highest in urban areas with a high percentage of impermeable surfaces, and in arid regions where vegetation is sparse.
Strategies to manage surface water flooding and coastal flooding fall into three categories: retreat, accommodate, or defend. Retreat moves settlements out of high-risk zones, maintaining setbacks from potential hazards. Accommodation provides room for water to collect without causing damage, displacement, or interruption. Defense strategies include natural and structural barriers to floodwaters.
Retreat may reduce the number of structures within the floodplain in order to avoid losses and restore a natural barrier to floods. Following Hurricane Sandy, residents of Staten Island, New York, led an exodus from an area of the borough that had flooded repeatedly. A group of 326 residents of Oakwood Beach and 107 in Ocean Breeze applied to sell their homes and relocate. New York State expects to pay about $200 million for these neighborhoods; it will demolish the houses, roadways, and infrastructure and restore the land as a natural barrier against storm surge. This type of landward retreat is available on Staten Island, but other coastal areas will experience coastal squeeze, narrowing the liveable area and leaving residents with nowhere to retreat. Managed retreats from flooding are happening in Louisiana, Pacific island nations, Panama, Bangladesh, and other at-risk coastlines, where the displaced residents are climate migrants looking for safer ground.
An option to horizontal retreat is the vertical retreat from floodwaters effected by elevating a structure. Constructing a building on a plinth or raised platform reduces the risk of flood damage. A "dry feet" strategy raises the base of the building so that floodwaters surround it, creating an island; in the Netherlands, this is known as a terp, an artificial mound that is safe from inundation. In contrast, a "wet feet" strategy accommodates water by establishing a permeable plane beneath a building, an area which can get wet without damaging the structure or contents.
Vertical retreat methods may safeguard the building occupants, but they do not address the potential for isolation during and after floods: children may be unable to go to school, work productivity is halted, supply chains and critical services are interrupted. In addition, there are constraints inherent in elevating existing buildings in urban environments. When single-family residences on small lots are elevated, there may not be adequate space for stair or ramp access. When multistory apartment buildings decommission units at floors below the design flood elevation, residents are displaced, and rental income is reduced for the building owner. When retail spaces are raised, the lack of connection to the street affects commercial viability and sales.
Accommodating stormwater creates more water retention capacity in the system. Philadelphia and other cities require new developments to collect the first inch of rainwater by means of green roofs, permeable ground cover, storage cisterns, and "water plazas," where the stormwater is captured, stored, and discharged slowly into municipal systems as they regain capacity (Logan, 2013). Water-conscious site planning restores the ability of a site to absorb and retain water; a permeable ground plane allows water to infiltrate below the surface, rejoin the water table and recharge groundwater supplies. In the public right of way, improvements such as permeable streets, infiltration strips, and urban forests help to manage urban stormwater; a single large tree can transpire 40,000 gallons (151,000 litres) of water per year (USGS, 2015), so afforestation is effective at managing intense precipitation.
The Dutch developed a series of methods to accommodate water in the "Room for the River" program: lowering sections of the flood plain, deepening river channels, relocating dikes to create a wider floodplain, removing obstacles from channels, and raising and strengthening dikes to retain more water. Water squares in Rotterdam are surrounded by housing, offices, churches, and schools, remaining dry recreation areas for most of the year. A light rainfall fills narrow trenches with water; if the rain continues, a stepped amphitheatre becomes a pool. Water in the basin is retained until the municipal system can process it, reducing the potential for flooding at adjacent sites. (De Urbanisten, 2015).
While it may be possible to provide room for the river, there isn't room to displace the ocean. Defense against storm surge occurs in floodable zones enhanced with landscaping, berms, and floodwalls. This approach adds multiple functions to the protective infrastructure, including multiuse pathways, recreational areas, water access, social amenities, and removable kiosks. The Dryline was designed to protect the tip of Manhattan from flood levels similar to Hurricane Sandy, which rose about 11.5 feet above mean sea level, according to the USGS Hurricane Sandy storm tide map. The Dryline was designed in a series of compartments which will be built incrementally, with supporting functions calibrated to fill gaps in each neighborhood (Figure 9). Although the height of the berm and floodwall is expected to provide only 1-in-100-year flood protection, completion of the first phase may establish the momentum to invest in longer-term solutions.
In the United States, construction activities in velocity zones (where storm surge is anticipated) require foundations engineered to withstand the forces of water: hydrostatic uplift (buoyancy due to submersion in seawater), hydrodynamic uplift (wave shear against the structural frame), debris effects (due to waterborne impact and damming), and scour (localized erosion). Walls are designed to equalize pressure below the design flood elevation, including "breakaway" framing that allows the structural frame to remain stable when water passes through, or flood vents aligned on opposing walls (FEMA, 2011). In velocity zones, beams must be placed above the design flood elevation, although other flood zones allow the finished floor elevation to be the measure of compliance.
Building foundations within floodplains may be deeper or have more mass than are necessary outside of the hazard zone, because of the variety of conditions encountered in these locations. Debris lodged against a building can exert pressure against the frame. Scouring may occur when water flows at high velocities past a piling, the repeated motion causing the soil to lose strength and create cavities around pilings in the wave runup (the inward rush) and rundown (return to the sea). In the aftermath of Hurricane Katrina along the Mississippi Gulf Coast, often the only remaining evidence of former inhabitations was the presence of concrete foundations and empty slabs along 60 miles of coastline.
Commercial uses may be compromised if they are located above the level of the sidewalk, so they are allowed to dry floodproof walls so that no more than 4 inches of water accumulates over a 24-hour period. Testing has shown that the most effective material to create watertight walls is a spray-applied pipe liner normally used for wastewater structures (Perkes, 2011). Dry floodproofing also requires flood gates to protect openings, and backflow preventer valves at sanitary sewer pipes to prevent contamination.
In contrast, wet floodproofing intentionally allows water to enter the building. Floodproof construction materials must be capable of direct contact with floodwater, which may contain pollutants, sewage, and other hazardous substances; materials must be able to be cleaned or require only cosmetic repairs and returned to service quickly. Acceptable materials include concrete, glazed brick, cement board, clay tile, marine-grade plywood, preservative-treated wood, composite lumber, steel wall panels, glass, and closed-cell spray foam insulation (FEMA, 2008).
Communities with severe flooding challenges, low wave action, and high development pressures are turning to innovative solutions, including floating structures. Prototypes for rebuilding the Lower Ninth Ward in New Orleans after Hurricane Katrina included the Float House by Morphosis Architects, designed with a buoyant polystyrene base. Services, including mechanical, electrical, and plumbing, were located within a base chassis covered with glassfiber-reinforced concrete. The floating base allows the structure to move vertically up to 12 feet, but it is prevented from moving horizontally by two steel mast anchors (Morphosis, 2009). This approach was based on floating structures in the Netherlands.
Major projects for community flood protection have been completed in the Netherlands to prepare for the 1-in-10,000-year flood, as well as in the Thames Estuary in the United Kingdom and the Venice Lagoon, places where the population density and the fragility of historic resources and world economies demand community-scale protective infrastructure. There are a wide range of community- and individual-scale adaptation measures available, but until communities enact the transformational changes necessary to support managed retreat, elevating and floodproofing individual structures will remain among the most common defences against flooding. The IPCC report states with high agreement, "For the 21st century, the benefits of protecting against increased coastal flooding and land loss due to submergence and erosion at the global scale are larger than the social and economic costs of inaction" (IPCC, 2014, p. 364).
Hydrological: Soil Subsidence
At first glance, soil subsidence may seem to be a geophysical hazard such as sinkholes, but the hazard has a direct relationship with climate. Subsidence may occur when large quantities of groundwater are withdrawn from soils consisting of fine-grained sediments, such as the clay found along riverbanks and coastal plains. Just as a dry sponge is thinner than a wet sponge, water in the soil is partly responsible for holding its shape. Air pockets are formed as water is removed, and this airspace allows organic matter to oxidize and shrink. Fine silt and clay particles settle into those pockets, causing soil layers to recede.
At the same time that soils are subsiding in floodplains, rising sea levels amplify the risk of flooding. In New Orleans, subsidence has caused the loss of as much as 12 feet of elevation since 1900, when mechanical pumps enabled the city's environs to be drained and subdivided, with the unintended consequence of causing ground levels to fall. Pumping wasn't the only reason for soil subsidence; clearing the cypress swamps halted organic soil accretion, and levees constructed along the length of the Mississippi prevented soil replenishment from alluvial material. The city used to be nearly 100% above sea level; a century after the pumps allowed the city to expand, about half of the metropolitan area has dropped below sea level.
Building foundations and utility connections are highly susceptible to soil movements. In the 1970s, several houses in newly developed areas of New Orleans experienced spontaneous explosions caused by gas line ruptures. The removal of groundwater formed a void beneath the slabs, allowing pipes to move or break, and volatile gas to build up below the slab (Campanella, 2015). As a result of these and other losses related to subsidence, foundations for new construction in the area use a grid of pilings driven deep enough to create resistance along the shaft of the pile. The process of driving the piles in cohesion-less soils disturbs the soil so that the tight grouping of piles increases the relative density of the soil. An alternative foundation method covers the building area with a "surcharge" of topsoil for several months before construction to establish a confining pressure for the soil underneath, compressing the top layer like a girdle. Pipe connections in areas of potential subsidence are fitted with flexible connections so that they do not pull apart from differential movement.
The desire to keep New Orleans dry created a destructive cycle: withdrawing groundwater caused the land to sink, rainfall pooled in the lower basins and required extraction, leading to further subsidence. Subsidence will cost the region an estimated $2.2 billion in damage to structures over the next 50 years (Waggonner & Ball Architects, 2013). The city is now moving to limit groundwater extractions, retain water where it falls, slow the flow of water across the landscape, and store large volumes of rainfall for infiltration. Rather than operating pump stations every time it rains, they will be activated only when necessary to handle heavy rainfall events or manage dry-weather flow. Reintroducing water into the soil through porous surfaces, exfiltration basins, and open space will slow the rate of subsidence, restore ecological health, and provide amenities for public life.
Subsidence is common in river delta plains along fragile coastlines, with more than half of the most rapidly subsiding lands in Asia; the Mekong Delta is subsiding at 1.6 cm per year, and Djakarta is sinking at an average rate of 5–10 cm per year. Solutions at the regional scale are infrastructural, such as shifting away from groundwater depletion and recharging aquifers, as well as architectural in nature, such as limiting the size and density of structures in susceptible areas. Cities such as Shanghai are creating land-use guidelines to address the weight of the urban crust and prevent the city from sinking.
Planning for Adaptation
The list of climate hazards is extensive and most communities face multiple hazards, resulting in events that will not be encountered one at a time but in groups of associated phenomena: subsidence and increased flooding; increasing temperatures accompanied by more intense hurricanes and higher storm surge. Cities living with climate-sensitive hazards are located in a variety of landscapes—floodplains, arid regions, and coastlines—and many of them are settlements that have survived 1,000 years or more, although they have never before experienced the rapid pace of change that is now occurring. Cities are central to exploring adaptive responses to hazards because of their population density, the diversity of social and economic activities, and the existing investment in the built environment. Climate-adapted cities will use these resources to mitigate climate change, test new approaches to manage climate hazards, and develop methods to adapt the built environment. Planning for adaptation responds to the observed and predicted climate hazards, guides development toward areas with lower vulnerability, and ensures that cities are not protecting themselves in a way that intensifies problems elsewhere.
Overcoming Barriers to Adaptation
Although it was popularly claimed that New Orleans, Louisiana, was tabula rasa after Hurricane Katrina, there still existed strong institutions, public utilities, supply chains, private ownership of lands, and street grids. Out of 188,250 housing units in Orleans Parish, 44% of structures did not have major damage (FEMA, 2006). In contrast with Bangladesh after Cyclone 2B, where one million homes were destroyed along with crops and industries, New Orleans had significant resources with which to rebuild.
There is considerable investment in the existing urban morphology, infrastructure, and structures that may make a community unwilling to abandon at-risk areas. The Urban Land Institute proposed shrinking the footprint of New Orleans after Hurricane Katrina, allocating recovery investments first to the highest and least-damaged areas, and deferring infrastructure repairs in the depopulated flooded neighborhoods. A city plan overlaid with six large circles indicating "Areas for Future Parkland" became known as the Green Dot Map, inspiring strong community sentiment, and motivating residents to demonstrate the viability of heavily damaged neighborhoods. (See "Disaster and Response in an Experiment Called New Orleans, 1700s–2000s.") Reconstruction of the city proceeded slowly, unevenly, and with heightened inequality. "Proposals for a building moratorium were almost universally rejected by residents… . More than 38,000 building permits have been issued for rebuilding to residents, ostensibly with <50% damage. Many homeowners succeeded in having their damage estimate reduced to below that key benchmark to enable rebuilding without elevation of the structure " (Kates, Colten, Laska, & Leatherman, 2006, p. 14656).
The reason for the resistance was the high cost of adaptation. New Orleans rebuilt protective levees to roughly the original height in order to meet a 1-in-100-year storm (authorized before Hurricane Katrina) at a cost of $4.5 billion. Increasing levee height to meet the 1-in-500-year storm required by the president's Executive Order 11988 (2015) would require an additional 3–4 feet in height along the entire system to guard against overtopping and storm surge. The Louisiana Coastal Protection and Restoration Study by the U.S. Army Corps of Engineers estimates that the cost for a system to protect the entire Louisiana coast would be in the range of $59–139 billion. The alternative would be to raise about 230,000 individual structures to 1 foot above sea level, at a cost of $23–28 billion (USACE, 2009).
Calculating the cost of adapting to meet climate-sensitive hazards assumes that there are resources available to design, implement, and maintain the necessary infrastructure that forms the basis for adaptation: shelter, mobility, energy, health, water, and other public services. However, there are many places where "adaptation deficits" determine adaptive capacity, because you cannot climate-proof infrastructure that is not there (Satterthwaite, 2008, p. 9). Less-developed countries have greater impacts from extreme weather than developed countries, and they are also less able to manage climate hazards, in part because of adaptation deficits.
Political pressures to maintain urban development can inhibit adaptation. The pressure to grow within a political boundary may conflict with moving people to safer ground, and the economic pressure to say "yes" to every opportunity may constrain future adaptive measures, such as retreating from the floodplain. Where housing is exposed to extreme hazards, it may be desirable to relocate occupants and transition settlements out of these zones into higher-density "receiving areas" for future growth and development, but residents within the community may protest the forced displacement, and the community at large may resist the intensification of density in receiving areas, or fail to financially support the transition.
Uncertainty regarding the location, extent, and timing of climate hazards also restricts adaptation, as the public perception that climate hazards are uncertain in timing or spatial distribution compounds the difficulty of encouraging investment in adaptation measures. Thinking of impacts as happening at some future time distances people from taking action; people are more likely to take greater risks with decisions that are not urgent and immediate (Spence, Poortinga, & Pidgeon, 2011). Without a recurring reminder of the potential consequences of inaction, competitive funding for projects may be shifted to more urgent and immediate needs. Maintaining an adaptation plan that inventories the existing built environment and its deficiencies, communicates long-term threats, creates comprehensive regulatory policies, and establishes a clear roadmap to meeting climate-sensitive hazards, is an effective step toward overcoming barriers to adaptation.
Community-Based Approaches
Changes to the built environment take shape in relation to individual property rights, and it is therefore essential to engage residents of the community in decision making related to proposed adaptation measures. Grassroots public engagement in the early design phases may contribute to a better understanding of conditions and influence the project outcome.
Community engagement during HUD's Rebuild by Design competition following Hurricane Sandy solicited an unprecedented amount of public input during the research phase. It was intended to increase awareness of disaster risk and resilience; get input from leaders, stakeholders, and residents to formulate well-integrated proposals; incorporate resiliency measures into existing policy; and educate leaders and the public about resilient design strategies (WB unabridged with Yale Arcadis, 2014). Groups of residents were invited to walking tours, design showcases, and brainstorming meetings to share their personal experiences, ideas, and perception of community needs and vulnerabilities.
The multidisciplinary Resilient Bridgeport team brought together local, state, and regional stakeholders to an All-Scales Workshop to examine the regional, city, and neighborhood scales, and identify potential climate impacts upon housing, transportation, environment, community identity, energy, emergency preparedness, and economic development. In an effort to assemble a thorough inventory of neighborhood concerns, the team met with adult education, high school, and university students; housing authority service providers and residents; environmental organizations; transit advocates; government agencies and elected officials; business owners, utilities, and industrial entities; nonprofits and enterprise groups; fishermen; and church congregations. Engagement was not limited to formal meetings and presentations, but included informal interactions such as a waterways tour, community bike ride, a lesson on the language of resilience at an adult education class, and community gardening. The premise underlying traditional planning is that highly complex problems require technical experts to anticipate and design the future (Hyman, 1990). The design team's efforts to capture grassroots impressions and ideas exposed the designers to messages from the nondominant interests. Raising awareness of climate-sensitive hazards among community stakeholders also gave them a role in advocating for future projects.
Among the persistent concerns in adapting to climate-sensitive hazards is equity. Neighborhoods that experience a higher than average share of climate impacts may be isolated by physical barriers, including poorly sited infrastructure or high-hazard topography, but also by economic barriers, including a lack of access to transportation and other services, a shrinking number or variety of places to live, and disinvestment by private companies that abandon at-risk areas. A significant concern is that only select disadvantaged groups will be forced to migrate from established communities, while property owners with greater resources will be allowed to remain by garnering support for adaptation measures due to their influence, or even by investing in infrastructure-scale protection using their own resources. Forced displacement undermines the social structure of a community, and has negative impacts upon the displaced population in health, productivity, and finances. Including members of the community from every economic sector ensures that they, in addition to the technical experts, have a voice in the future of their community, reducing inequity in the process of adaptation.
Delivering Multiple Benefits
In many cities, the existing built environment is not maintained in adequate condition to meet current operational needs; neither does it have the capacity to handle periodic severe weather events. Adaptation measures may not respond equally to long-term stresses, current climate events, and the potential for future changes. Adaptation costs may be high, and the needs widespread, so communities must prioritize adaptation measures based on a number of variables: how many people they will protect, the magnitude of avoided losses, the cost of the improvements, the service life of the project, and whether they will deliver multiple benefits.
Adaptation measures that are relatively cost-effective against climate hazards now, and under a range of future climate scenarios, are considered low-regret actions. One proposed low-regret measure is to repair leaking water systems. The World Bank estimates up to 60% of the worldwide drinking water supply is lost to leaking pipes and fixtures, and repairing these systems will conserve potable water supplies that are shrinking as a result of drought. Fixing the infrastructure reduces the cost of extracting, treating, and delivering water, thereby providing a way to recover maintenance costs.
"Win-win" measures manage several climate risks at once, making these high priority actions. Afforestation reduces the urban heat island effect, resulting in lower temperatures on the street and in neighboring structures. Planting trees also helps to manage stormwater by capturing water in leaves and bark and releasing it through transpiration, reducing surface water flooding. Roots increase the soil infiltration capacity and rate, allowing groundwater to recharge. Win-win measures may deliver social and economic benefits as well; in the example above, tree-planting improves air quality, reduces energy costs for nearby structures, and extends the service life of asphalt roadways in shaded areas (Casey Trees and Davey Tree Expert, 2016).
Adaptation requires long-term investment. Just as the value of investments in public transit, education, or open space may not become evident for many years, adaptation measures may not have a clear, certain, or short-term return on investment. Economic calculations may demonstrate the benefits of adaptation measures as avoided losses viewed only in hindsight. For these reasons, collateral benefits can influence the public perception and financial viability of proposed projects.
A Framework for Integrated Planning
It is easy to respond to a catastrophe with bombastic promises to rebuild bigger, better, and stronger than ever. But preparing for a changing climate and the hazards that will result requires careful assessment and thoughtful preparation so as not to rely on emotional decisions made in the aftermath of a disaster, or to act in ways that constrain future adaptation. Constraining actions include allowing development in locations susceptible to climate-sensitive hazards, degrading ecological habitat, or building in ways that protect one area but intensify problems elsewhere. Integrated planning creates a self-reinforcing model to maximize the potential value of designing to address climate hazards and reduce the cost of implementation.
An integrated plan for reducing disaster risk in the built environment creates awareness of climate-sensitive hazards; develops alternatives based on different scenarios; tests adaptation methods before fully committing resources; implements portions of the plan as opportunities arise; evaluates their efficacy and builds a continuous loop of action and evaluation. This model allows the community to match its development practices and policies to its long-term vision.
Creating awareness of climate threats ensures that communities and residents have access to scientifically supported models of potential hazards, and clear communication methods help them understand the potential impacts on cities, structures, and people. Effective communication plans are sustained, cohesive, and ubiquitous; they explain how to prepare for, respond during, and recover from a crisis. Disseminating information on adaptation measures and supporting adaptation action may reduce the need for postdisaster assistance in what is known as the "Resilience Dividend." Disaster effects on the built environment are reduced by preparation; a report by FEMA shows that $1 in funding spent to mitigate the impact of natural hazards provides $4 in future benefits (NIBS, 2005).
Developing scenarios with alternate plans to address a variety of conditions is commonly used in emergency planning. Guidelines for response and recovery are established prior to an event in order to shorten the response time and reduce disaster impacts. Recovery plans may include case studies for structures that are customizable if the actual damage is different from the predicted damage. New York City's guideline A Stronger, More Resilient New York, published following Hurricane Sandy, identified adaptation actions for rebuilding, repairing, and retrofitting housing units for flood resilience (NYC, 2013). Scenarios might identify structures that will not be "grandfathered" in the event of future disasters, and designate receiving areas for new population growth in a managed-retreat scenario.
Implementation will construct, rehabilitate, or modify the built environment to match the selected design parameters. Conditions which trigger the implementation phase may depend on a set of predetermined thresholds; thresholds may address persistent problems or events that develop suddenly. For example, the impetus for homeowner buyouts may be the groundwater aquifer shrinking to a specified percentage of its current capacity or repetitive flood events. The implementation phase typically includes a group of project partners who contribute funding or other support, and they should be consulted in the planning stages. Implementation depends on community support as well, reinforcing the need for community engagement to avoid lengthy challenges and delays.
The complexity of climate-sensitive hazards is rivalled by the convoluted network of approvals a project must navigate in order to become a reality, particularly when a project has no precedent. Many adaptation projects are new in scope or scale, such as the Sears Point wetland restoration in San Pablo Bay near San Francisco; it required permits from seven county, state, and federal agencies. The project required 10 years of work to complete, including seven years of environmental studies and three years of construction to turn 1,000 acres of ranch land into a tidal marsh habitat intended to restore a shoreline buffer to sea-level rise (King, 2016). Consolidating the approvals process into a single, interagency group would handle future projects of this complexity with a predictable and reasonable timeline for approval.
Evaluating the efficacy of hazard-mitigation measures is essential. The built environment must remain viable as conditions change, and evaluation provides input for the next planning and implementation efforts, valuable experience for the next consequential event. A framework for change requires a coherent vision that is purposeful and sustained, but because the process is incremental and iterative, phases may be continuous and overlapping, without clear divisions between one phase and another. Monitoring completed projects, reevaluating, and refining the adaptation plan will ensure that it uses current data for hazard conditions, incorporates new discoveries, and emulates proven successes.
Adaptation and hazard-mitigation planning establish the process to transform the built environment to meet the community's vision for the future. In the global progress toward urbanization, environmental challenges have been met before: resource challenges, severe weather, and societal pressures. Planning ensures that communities will not lose the integral qualities of place and their unique identity. The advent of climate change may exacerbate these concerns, but adaptation in the built environment will sustain human populations when disaster strikes, and establish a foundation for social and economic recovery.
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