Extreme Heat: Impacts, Vulnerabilities, and Mitigation Strategies Executive Summary

Extreme Heat: Impacts, Vulnerabilities, and Mitigation Strategies Executive Summary Extreme heat events are escalating in frequency, intensity, and duration globally, driven by climate change and exacerbated by the Urban Heat Island (UHI) effect in cities. These events pose significant threats to human health, economic productivity, and environmental systems. Vulnerable populations, including older adults, those with mental and chronic health conditions, outdoor workers, and low-income communities, face disproportionately higher risks. While active cooling solutions like air conditioning provide immediate relief, they contribute to the problem by increasing energy demand and greenhouse gas emissions. Effective mitigation strategies require a multi-faceted approach, combining early warning systems, urban planning focused on green and cool infrastructure, and targeted support for at-risk communities. I. The Escalating Threat of Extreme Heat A. Global Warming and Heatwave Trends The Earth is experiencing a rapid increase in average temperatures, with July 2023 being the "hottest month on record" globally, and 2024 projected to be even hotter. "Since the early 20th century, average air temperatures have changed by different amounts in different parts of the United States." This warming is primarily attributed to human-induced greenhouse gas emissions. Key trends include: Increased Frequency and Intensity: "The frequency, duration and intensity of extreme heat and heatwaves in the UK has been increasing." Studies project that an extreme heat event occurring once every 20 years could happen every two to four years by the end of this century under high emissions scenarios. The number of days exceeding 100°F is projected to dramatically increase across the U.S. Longer Duration: Heatwaves are lasting longer, with the "land area affected by heat waves is expected to double by 2020 and quadruple by 2040." Earlier Onset: Heatwaves are starting earlier in the year. Record-Breaking Events: Notable heatwaves include the 2003 European heatwave (causing 70,000 excess deaths, primarily in France and Italy), the 2010 Russian heatwave (55,000 excess deaths), and the 2021 Pacific Northwest heatwave (over 800 reported deaths). The 2023 Western North American heatwave, fueled by record-warm Atlantic Ocean temperatures, affected over 100 million people, caused over 200 deaths, and resulted in $14.5 billion in economic loss. B. Urban Heat Island (UHI) Effect Cities experience significantly higher temperatures than surrounding rural areas due to the Urban Heat Island (UHI) effect, which "is the dominant driver of recent warming in large cities." Temperature Discrepancy: Urban areas are approximately 1.5°F warmer than rural areas and are "warming more rapidly over time than rural areas." This effect is "typically largest in the summer." Causes of UHI:Reduced Vegetation: Urbanization leads to less vegetation, reducing natural cooling through shade and evapotranspiration. Highly developed areas with 75-100% impervious surfaces have significantly less evapotranspiration. Impervious Materials: Replacement of natural landscapes with dark, impervious surfaces (e.g., asphalt, concrete, dark rooftops) that absorb and store more solar radiation. Solar reflectance (albedo) and thermal emittance play crucial roles in how much heat a surface absorbs and sheds. Urban Geometry: Dense urban structures can trap heat, limiting the release of long-wave radiation at night. Waste Heat: Anthropogenic heat from vehicles, industry, and building air conditioning systems further contributes to urban warming. II. Impacts of Extreme Heat A. Human Health and Comfort Extreme heat is the "deadliest weather-related hazard," causing more deaths annually than hurricanes, tornadoes, and floods combined. Physiological Stress: Heat exposure overwhelms the body's thermoregulation, leading to increased blood flow to the skin and sweating. When these mechanisms are insufficient, core body temperature rises, leading to heat-related illnesses such as heat rash, heat syncope, heat cramps, heat exhaustion, and life-threatening heatstroke. Exacerbation of Chronic Conditions: High temperatures worsen symptoms of pre-existing chronic diseases like cardiovascular, respiratory, renal, and diabetes. "An average of 1,780 yearly hospital admissions were associated with warm days in England between 2010 and 2018." Mental Health Impacts: Extreme heat is linked to heightened irritability, aggression, intimate partner violence, and suicide. Studies show an increased risk of emergency department visits for mental health conditions during heat events. Individuals with mental illness may be "less likely to be aware of the health risks posed by extreme heat and less likely to follow public health directives and to receive and comprehend warnings." Medication Interactions: Many commonly used medications (e.g., anticholinergics, antidepressants, antipsychotics, diuretics) can impair thermoregulation, increase dehydration risk, or have their efficacy or toxicity altered by heat. Sleep Disruption: Elevated nighttime temperatures prevent adequate cooling, leading to sleep loss and impaired brain cognition. Heat-Related Mortality: The summer 2022 heat periods in England were associated with 2,985 deaths. Projections for the Tampa Bay area estimate 242 heat-related deaths annually by 2030, surging to 1,059 by 2060. "More than a third of urban heat-related deaths in the 1990s and early 2000s can be attributed to climate change." B. Vulnerable Populations Certain groups are disproportionately affected by extreme heat due to a combination of biological, socioeconomic, and environmental factors. Older Adults: Persons aged 65 and older are at highest risk due to impaired thermoregulatory responses, chronic health conditions, medications, social isolation, and living in substandard housing. The global population aged 69+ exposed to dangerous acute heat (TMAX95 > 37.5°C) is projected to increase by 177–246 million by 2050. Infants and Young Children: Highly susceptible to physiological stress, illness, and death, partly because they are dependent on adults for protection and may not recognize risks or have access to water. Outdoor Workers: Particularly vulnerable (e.g., agriculture, construction, street vendors) due to direct and prolonged heat exposure and physically demanding tasks. Heat stress can result in significant income loss, with women homeworkers in South Asia experiencing up to 30% income loss. Low-Income Communities and Homeless Individuals: Limited access to cooling tools (fans, AC), substandard housing (poor ventilation/insulation), and lack of access to cool public spaces or drinking water exacerbate their risk. Homeless individuals in London showed a higher risk of hospitalization during heatwaves. People with Disabilities and Chronic Illnesses: Impaired mobility, cognitive functioning, and specific health conditions increase their susceptibility. Communities of Color: Systemic racism and historical disinvestment have led to "disparate health, economic, environmental, and social outcomes," with these communities often located in hotter neighborhoods with less green space and poorer air quality. Black women, for instance, face higher rates of prenatal hospitalization due to heat exposure. Women and Girls: In some regions, women play a key role in food security and often eat last, exacerbating food insecurity during crises. They are overrepresented in informal and vulnerable outdoor occupations, leading to higher income loss due to heat. Droughts also increase their burden of unpaid care work, particularly water collection. C. Economic and Social Impacts Extreme heat has broad economic and social consequences. Reduced Labor Productivity: Heat stress significantly reduces labor capacity and productivity globally, with greater losses in low and medium Human Development Index (HDI) countries. India and Cambodia experienced significant per-capita work hour losses in 2019. Increased Energy Demand: Rising temperatures drive increased demand for active cooling (AC), leading to higher electricity consumption and peak demand, straining power grids and increasing energy costs. Food Insecurity: Heatwaves and associated droughts reduce crop yields and fish stocks, impacting global food security. This disproportionately affects women in some regions who are responsible for food production and provision. Infrastructure Strain: Extreme heat impacts grid resilience, transportation (railway, roadway, pipelines), and other critical infrastructure. Violence and Crime: Heat is linked to heightened irritability, aggression, and intimate partner violence. "Each degree Celsius increase in annual temperatures is associated with a nearly 6% average increase in homicides." Water Quality and Supply: Elevated temperatures can impact water quality and reduce water supply, exacerbating drought conditions. III. Mitigation and Adaptation Strategies Effective heat resilience requires a multi-pronged approach involving urban planning, building design, public health interventions, and policy. A. Urban Planning and Green/Blue Infrastructure These strategies aim to reduce the UHI effect and create cooler urban environments. Trees and Vegetation: Expanding the urban tree canopy cools land surface temperatures by 20-45°F (11-25°C) and air temperatures by 2-9°F (1-5°C) through shade and evapotranspiration. This also improves air quality and stormwater management. Austin's plan includes "Pilot cool corridors by designing and deploying cooling strategies such as trees and built shade on high-heat corridors." Green Roofs and Walls: Installing green roofs and living walls reduces heat absorption, improves air quality, and decreases energy consumption. Washtenaw County's "Hickory Way Apartments" project used Energy Star-rated white roofing material to reduce UHI. Accessible Parks and Green Spaces: Increasing and enhancing urban green spaces provides accessible cool areas for communities, addressing historic inequalities in their distribution. Permeable Pavement: Allows water infiltration, reducing runoff and cooling surfaces, though less effective when dry and requires maintenance. Stormwater Management: Blue-Green Infrastructure (BGI) like rain gardens and bioswales can manage stormwater, reduce runoff, and enhance urban cooling. Cool Corridors: Designing "cooling corridors" with increased shading along pedestrian and cycling routes to connect existing green spaces and community assets. B. Heat-Resilient Building Practices Modifying the built environment is crucial for protecting communities indoors. Cool Surfaces (Roofs, Walls, Pavement): Utilizing materials with high solar reflectance (albedo) and thermal emittance can significantly reduce heat absorption by buildings and urban surfaces. A global 1% net increase in rooftop and pavement albedo could offset 44 Gt of CO2 emissions. Energy Efficiency Audits and Retrofits: Identifying and addressing energy waste in buildings reduces consumption, lowers cooling costs, and enhances resilience. Passive Cooling Solutions: Incorporating design elements like smart ventilation, shading structures (overhangs, awnings, shutters), and optimized building orientation to maximize natural light while minimizing solar heat gain. Heat-Resilient Design in New Developments: Incentivizing and codifying heat-resilient design elements in new constructions, including advanced technologies, facade upgrades, and building materials. City-Owned Buildings: Embedding heat-resilient design and assessing existing standards in municipal buildings. C. Public Health Interventions and Early Warning Systems These strategies focus on protecting human health and ensuring timely response to heat events. Heat Health Warning Systems (HHWS): Vital for translating complex weather data into clear, actionable guidance. Philadelphia's system, implemented in 1995, is a successful example, credited with saving lives through airmass classification and tailored interventions. Many European countries have HHWS, but criteria and effectiveness vary. Public Awareness and Education Campaigns: Educating communities on heat risks, high-risk populations, and appropriate protective actions (e.g., hydration, staying indoors, using cooling methods, avoiding strenuous activity). Trusted messengers are key for effective communication. Cooling Centers and Spaces: Establishing and promoting accessible cooling centers (e.g., libraries, community centers, splash pads) in high-heat vulnerable neighborhoods. Austin's plan includes co-designing "cooling pathways to trusted community spaces." Mobile solar trailers can also serve as cooling centers during power outages. Cooling System Distribution Programs: Providing financial support (e.g., LIHEAP) and distributing cooling units to vulnerable populations. Labor Standards for Heat Safety: Mandating heat safety training, hydration breaks, access to shade, cool-down periods, and adjusting work schedules for outdoor workers. Washington State has an "Outdoor Heat Safety Program." Health Sector Preparedness: Training healthcare professionals on heat-health impacts, identifying at-risk groups, and managing heat-related illnesses. Hospitals and care homes need to ensure thermal comfort and have plans for increased admissions. D. Policy and Governance Integrating heat resilience into policy and planning frameworks is essential for long-term adaptation. Formal Recognition of Extreme Heat: A pressing need to formally recognize extreme heat at all levels of government to unlock necessary resources and funding, similar to other natural disasters. Comprehensive Heat Action Plans (HAPs): Developing integrated plans that assess vulnerabilities, plan interventions, and ensure cross-sector collaboration (government, private sector, CBOs, academia). Funding and Incentives: Leveraging federal programs (HUD, EPA, DOE) and exploring additional incentives for heat-resilient design and green infrastructure. Incorporating Heat Resilience into Capital Improvement Programs: Ensuring all relevant capital projects embed heat resilience elements and monitoring their implementation. Research and Evaluation: Continuous research into heat-health relationships, evaluation of intervention effectiveness, and addressing knowledge gaps (e.g., indoor thermal loads, specific physiological responses of vulnerable groups). Conclusion The increasing threat of extreme heat necessitates urgent and comprehensive action. By understanding the multifaceted impacts and vulnerabilities, and implementing integrated mitigation and adaptation strategies—from urban design to public health initiatives and policy changes—communities can build long-term resilience and protect their populations from this escalating climate hazard. While air conditioning offers immediate relief, the focus must shift towards sustainable, equitable solutions that reduce reliance on fossil fuels and address the root causes and exacerbating factors of urban heat.