Center for Health
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EnvironmentClimate Health and Risk Tool

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CHaRT: Climate Health and Risk ToolPublished: 06/21/2023 by Tim Sheehan

CHaRT is an interactive, web-based tool that exposes the level of health risk from a specific climate hazard and exposes the factors that drive that risk. Here we provide a high level introduction to CHaRT.

Fuzzy Logic ModelingPublished: 06/21/2023 by Tim Sheehan

CHaRT models use a decision modeling approach called fuzzy logic. Fuzzy logic is a system based on natural language that recognizes that people have individualized or subjective perspectives that affect decisions. This document provides a brief and understandable introduction to fuzzy logic.

General GuidancePublished: 06/20/2023 by Tim Sheehan, PhD

Drivers of heat health risk vary from location to location. CHaRT provides guidance to reduce risk from specific drivers. This document provides background on how the heat health model considers risk and provides links to all of CHaRT's heat health risk reduction guidance.

Worker ProtectionsPublished: 06/20/2023 by Alan Wang, BA, Jeremy J. Hess, MD, MPH

With rising global temperatures, workers may be increasingly required to work in hot environments, and will be more susceptible to heat stress, occupational injuries, and potentially decreased productivity. Importantly, heat stress for workers derives from both external sources of heat in the environment as well as internal sources including metabolic activity, which is increased during physical activity. Heat stress can be amplified by personal protective equipment that reduces evaporative cooling through sweating. Workers are at risk for dehydration, occupational injuries, absenteeism, and chronic kidney injury, as well as decreased productivity, which can affect wages. Individuals working in industries that require strenuous physical activity, outdoor operations, and exposure to high-temperature environments are the most vulnerable. Worker protections are interventions put in place to protect workers from heat exposure and heat stress, and generally fall into the categories of infrastructure changes, administrative or work practice changes including empowering workers to pace themselves in their work, and personal protective equipment. Policies may be implemented at multiple levels but ultimately play out at the worksite and workers individually. There is a wide range of specific potential interventions, with varying costs, implementation timelines, and degrees of environmental sustainability. Consensus recommendations for US workplaces are available. While some more effective interventions have higher upfront costs, these costs are likely to be at least partially offset through increased worker health, productivity, and retention.

Air ConditioningPublished: 06/19/2023 by Alan Wang, BA, Jeremy J. Hess, MD, MPH

Air conditioning, which mechanically cools indoor air, can be installed in a single room or building. Air conditioning strongly protects against adverse health impacts during extreme heat, and is on track to be the leading intervention against extreme heat globally. Air conditioning can be implemented quickly, over hours to days depending on the type of installation. Implementation costs from several hundred dollars for a window unit up to several thousand for air conditioning an entire home. While strongly protective, air conditioning is costly to install and operate and is not equitably distributed; its use can also contribute to air pollution and carbon pollution. Multiple more sustainable, albeit less effective, cooling strategies are available, and strategies for subsidizing installation and operating costs can decrease inequities in air conditioning distribution and utilization.

Behavioral InterventionsPublished: 06/19/2023 by Alan Wang, BA, Jeremy J. Hess, MD, MPH

Behavioral interventions to reduce heat risks to health include a variety of actions and lifestyle changes to reduce indoor temperatures, reduce body temperature, increase individuals’ recognition of heat-related illness in themselves and others, and increase the likelihood that affected individuals will seek care early when feeling ill. Interventions include indoor cooling with air conditioning or evaporative coolers; individual cooling strategies including fans, dousing, foot immersion, misting, and cool showers; staying hydrated; and education to increase recognition of heat-related illness and how to seek help. Most are implemented at the individual or household level and can be implemented quickly and cheaply, though air conditioning and evaporative coolers are more expensive to install and operate. Many vulnerable groups are not able to utilize behavioral interventions as easily or effectively as other groups. Ideally, behavioral interventions are part of a constellation of interventions at multiple levels to protect vulnerable individuals and communities.

Heat Early Warning Systems and Action PlansPublished: 06/19/2023 by Jeremy J. Hess, MD, MPH, Kristie L. Ebi, PhD, MPH

Heat early warning and response systems and action plans are interventions that combine weather forecasts with previously-defined temperature thresholds for action with pre-planned response activities in health and other sectors; they are often combined with heat action plans that outline longer-term changes in urban planning and other areas to prepare for a hotter future. Heat early warning systems and action plans typically take several years to implement and are effective at reducing morbidity and mortality in highly vulnerable groups, although they may not reduce mortality in the general population and are unlikely to completely offset the health risks associated with extreme heat events. While cost estimates are rare, heat early warning systems and action plans are considered highly cost effective with few downsides.

Green RoofsPublished: 06/19/2023 by Alan Wang, BA, Jeremy J. Hess, MD, MPH

Green roofs are roofs covered with vegetation and are considered a nature-based climate solution. Extensive green roofs use hardy plants and require little maintenance, while intensive green roofs resemble gardens or parks and require more maintenance. Green roofs cool their buildings and the surrounding environment through absorption of solar radiation and evapotranspiration. They benefit health by reducing the temperature of indoor environments; they can also reduce air pollution and improve mental health through nature contact. There are no studies that have directly observed impacts of green roofs on health care utilization or mortality. In simulations, widespread green roof adoption reduced indoor air temperatures 2-3°C (3-5°F), reduced population-weighted summertime temperature by 0.35°C (0.63°F), and reduced heat-related mortality by 0.21%. Green roofs are more expensive than conventional roofs to install and maintain but last about twice as long, yielding a small net cost premium that is considered marginal over the roof’s lifetime. Alternatives to green roofs include high albedo (highly reflective) roofs, though these roofs also retain less solar radiation in winter, resulting in higher heating costs.

Tree Cover and GreenspacePublished: 06/19/2023 by Alan Wang, BA, Jeremy J. Hess, MD, MPH

Increasing urban tree cover has multiple health benefits, one of the most dramatic of which is reduced heat-health risks. Trees reduce urban heat islands and thereby reduce heat hazard intensity and thus adverse health effects of heat exposure. Tree canopy cover of at least 30% to 40% is optimal for health protection, and simulation studies have found that increasing tree canopy cover to this level results in reductions of hundreds of heat-attributable premature deaths annually in medium to large cities in Europe and the US. There are few reports of the implementation time or cost of large scale tree planting campaigns. Young trees generally require decades to mature and other health protections should be considered in tandem with tree planting, particularly in highly impacted communities, in order to provide immediate benefits while tree canopy interventions reach their maximum impact over several decades.

Heat-Health SurveillancePublished: 06/17/2023 by Jeremy J. Hess, MD

Surveillance is the systematic collection, analysis, utilization, and sharing of health data with stakeholders in order to support public health programming. Surveillance for heat-related disease and death supports the efficiency and effectiveness of public health interventions to reduce risk. Common early indicators include emergency medical service calls, emergency department utilization, and hospitalization; mortality is a lagging indicator. Information on hazard exposure and population vulnerability are important additional data streams. Surveillance for heat-health impacts can be incorporated into existing surveillance platforms; implementation typically takes several years. While there are no cost-effectiveness estimates for heat surveillance, specifically, surveillance activities are highly cost effective, particularly for commonly encountered hazards with high mortality risk in large populations.

Indigenous AdaptationPublished: 06/14/2023 by Jeremy Hess, MD

We are currently developing guidance specific to the needs of Indigenous individuals and communities. We anticipate its completion by July 30, 2023.

Albedo Management Using Cooling MaterialsPublished: 06/13/2023 by Alan Wang, BA, Jeremy J. Hess, MD, MPH

Albedo is a measure that quantifies the proportion of incoming radiation reflected from a surface (from 0 to 1). Higher albedo materials reflect more shortwave radiation. In the built environment – principally in roofing and paving – these materials reduce heat hazard intensity and thus health impacts. Most urban environments have albedos between 0.15 and 0.2. There are no studies that have directly observed impacts of albedo management on health care utilization or mortality. On average, in simulation studies, increasing urban environment albedo by 0.1 drops temperatures by 0.09°C (0.16°F) and heat-related mortality by 1.8%. Albedo management is more effective when combined with other strategies, particularly increasing urban vegetation. The literature regarding the timing and cost of implementation is limited. Materials for increasing pavement albedo are approximately $7 per square meter (m2) or $6,250 per city block. Approximate installation costs for a new high albedo flat roof are $28/m2 and $80/m2 for a new high albedo residential pitched roof.

Cooling CentersPublished: 06/10/2023 by Jeremy J. Hess, MD, MPH

Cooling centers are cool public or private spaces that welcome people seeking shelter from heat. Ideally, cooling center interventions include communication plans to promote awareness and transportation plans to promote access. There are no studies on their effectiveness, though retrospective observational studies show a protective effect of visiting cool spaces during heat waves, and laboratory simulations show a protective effect while in the cool space that diminishes quickly after heat exposure resumes. Cooling centers leveraging existing spaces can be implemented quickly and cheaply, but more comprehensive planning and service provision requires additional costs. There are no estimates of the resources or timing required to implement a cooling center intervention.

FansPublished: 06/10/2023 by Alan Wang, MA, Jeremy J. Hess, MD, MPH

Electric fans promote cooling through convection (heat transfer to a fluid, in this case air) and evaporation (heat transferred into the process of water vaporization). Fans are effective at reducing heat stress and promoting thermal comfort, though there is no evidence regarding their effectiveness specific to preventing unplanned health care visits, hospitalization, or death. Fans are more effective for healthy younger adults and people who sweat normally and are not recommended as a cooling strategy for elders on common medications above 37°C (99°F). Fans are relatively inexpensive to obtain and operate, are widely available, and provide immediate relief when operated. There is no evidence regarding implementation of fan distribution programs. Fans should not be used as a sole cooling strategy at high temperatures (above 45°C [113°F]) and ideally would be used as part of a suite of individual cooling strategies, many of which are at least as effective.