Heat-associated deaths and illnesses, vulnerabilities to chronic disease, and other health risks to people in the Southwest result from increases in extreme heat, poor air quality, and conditions that foster pathogen growth and spread. Improving public health systems, community infrastructure, and personal health can reduce serious health risks under future climate change.
Exposure to hotter temperatures and heat waves has led to heat-associated deaths and illnesses in Arizona and California.398,399,400,401,402,403 In the unprecedented 2006 California heat wave, which affected much of the state and part of Nevada, extremely high temperatures occurred day and night for more than two weeks.404 Compared to non-heat wave summer days, it is estimated that the event led to an additional 600 deaths, 16,000 emergency room visits, 1,100 hospitalizations in California,399,405,406 and economic costs of $5.4 billion (in 2008 dollars).405 Parts of the Southwest region experienced record-breaking heat in five of the six years from 2012 to 2017.25,26,27,28,29 Assessments of the health impacts associated with record high temperatures in parts of the Southwest since 2010 are not yet available in the scientific literature.
Under continued climate change, projected increases in hot days and extreme heat events in the Southwest (Figure 25.10)23,24,404,407 will increase the risk of heat-associated deaths.30 Under the higher scenario (RCP8.5), the Southwest would experience the highest increase in annual premature deaths due to extreme heat in the country, with an estimated 850 additional deaths per year and an economic loss of $11 billion (in 2015 dollars) by 2050.178 Under a lower scenario (RCP4.5), deaths and costs would be reduced by half compared to the higher scenario (RCP8.5).178 By 2090, deaths and economic losses would more than double from 2050 under all emissions scenarios.178 Heat and other environmental exposures particularly affect outdoor workers.178 Under the higher scenario (RCP8.5), extreme heat in the Southwest (Figure 25.10) would also lead to high labor losses, including losses of high-risk labor hours of up to 6.5% for some counties by 2090 and of $23 billion per year in regionwide wages (in 2015 dollars).178 It is projected that the lower scenario (RCP4.5) would reduce those wage losses by half.178
The risk of illness or death associated with extreme temperatures can be reduced through targeted public health and clinical interventions.30,32 The main factors that put individuals and populations at increased risk in a heat wave are age (children and older adults are most at risk), hydration status, and presence of a chronic disease such as obesity, cardiovascular or respiratory disease, or psychiatric illness.400,408,409,410,411,412,413,414,415 Psychosocial stresses and socioeconomic conditions, such as hot and poorly ventilated homes or lack of access to public emergency cooling centers can elevate these risks.31,33,416
Without adoption and implementation of strategies to minimize exposures to extended periods of extreme heat, the public health impacts of future heat waves may be as serious as those observed in California in 2006. The technological and behavioral adaptations to heat developed by populations in the Southwest are based on the observed historical range of nighttime minimum temperatures.404 Projected increases in minimum temperatures and decreases in the number of cool nights23 may diminish the efficacy of these adaptations.
Climate change and variability can also increase communicable and chronic disease burdens.417,418,419 While infectious diseases like plague and hantavirus pulmonary syndrome disproportionately affect the Southwest region,158 new research to support estimating future climate-associated risk for these diseases is sparse.420 Therefore, this assessment focuses on recent developments in the understanding of heat, air quality, mosquito-borne diseases, and Valley fever and vulnerabilities that influence them.
In addition to extreme heat, the environmental conditions of greatest concern for human health are ground-level ozone air pollution, dust storms, particulate air pollution (such as from wildfires and dust storms), aeroallergens (airborne substances that trigger allergic reactions), and low water quality and availability.30,178 In addition, alternating episodes of drought and extreme precipitation coupled with increasing temperatures promote the growth and transmission of pathogens.30,421 The risk of onset or exacerbation of respiratory and cardiovascular disease is associated with a single or a combined exposure to ground-level ozone pollution, particulate air pollution, respiratory allergens, and extreme heat. Ground-level ozone is produced by chemical reactions of combustion-related chemicals (for example, from vehicles or wildfires) in a reaction that is dependent on ultraviolet radiation (that is, from the sun) and amplified by higher temperatures. Once formed, ozone can travel great distances and persist in high concentrations overnight in rural areas. Among many health impacts, ozone can promote or aggravate asthma and respiratory allergies.422,423,424,425
Elevated levels of CO2 in conjunction with higher temperatures can increase the amount and potency of aeroallergens (Ch. 14: Human Health, KM 1). These conditions may also lead to new cases or exacerbation of allergy and asthma.426,427,428,429 Mortality risk during a heat wave is amplified on days with high levels of ground-level ozone or particulate air pollution, with the greatest mortality due to cardiovascular causes.430
Severe dust storms in the Southwest contribute to respiratory and cardiovascular disease.431,432 The association between Valley fever, a soilborne fungal respiratory infection of the Southwest, and warmer temperatures and soil dryness varies across the region and by time of year.189,433,434 The connection between climate change, dust storm frequency and severity, and future public health effects in the region is complex and remains an emerging area of research.435,436,437,438,439 Heat extremes, warming, and changes in precipitation will also influence the distribution and occurrence of vector-borne diseases like West Nile virus440,441,442,443 and may lead to the emergence of new disease (Ch. 14: Human Health, KM 1).30 Without proactive interventions and policies that address the biological, exposure, and socioeconomic factors that influence individual and population vulnerability, adverse health impacts may increase (Ch. 14: Human Health, KM 2). Those increases may disproportionately affect people with the lowest incomes, which hinders adaptive capacity (Ch. 14: Human Health, KM 1).416,444
Climate-related hazards such as heat waves, flooding, wildfires, or large disease outbreaks require emergency responses. Prolonged droughts can affect drinking water availability, reduce water quality,445 and send more people seeking medical treatment.446,447 The increased burden of disease can outpace the resources and adaptive capacity of public health and clinical infrastructures. The region may not be prepared to absorb the additional patient load that could accompany climate change,448 but integrating risk reduction strategies into emergency response plans and recognizing and addressing vulnerability factors can appreciably reduce risks of future adverse health consequences (Ch. 14: Human Health, KM 3). This approach is embodied in the Centers for Disease Control and Prevention’s (CDC) Building Resilience Against Climate Effects framework for adaptation planning.449 Adaptation planning is already yielding health protection benefits.450
Local government agencies are preparing for extreme events by developing and updating emergency response plans and improving public warning and response systems. In 2014, California updated its Contingency Plan for Excessive Heat Emergencies,451 Arizona released its Heat Emergency Response Plan,452 and Salt Lake City, San Francisco, and Sonoma County were recognized in the first cohort of U.S. Department of Energy Climate Action Champions. Integrated and participatory planning for extreme heat,453 such as the Capital Region Climate Readiness Collaborative in Sacramento, California, can help overcome institutional and governance barriers to implementing adaptation actions (Ch. 28: Adaptation).454
Policies and interventions related to one health factor can positively affect other factors and yield co-benefits455,456,457,458,459 For example, research shows that heat-associated deaths and illnesses are preventable460 and that healthier individuals are less susceptible to adverse effects of extreme heat exposure. Obesity, which affects about 30% of adults and 15% of school-age children and teens nationwide, increases the risk for many chronic diseases, such as asthma and diabetes, and increases the risk for serious heat-related adverse health outcomes.32,461,462,463 Access to healthcare, social isolation, housing quality, and neighborhood poverty are also key risk factors for heat-related health impacts.31,33,412
Urban design strategies to address these risk factors include increasing walkability and bicycle safety and maintaining and planting trees and green space.464 These strategies can achieve multiple health benefits, including increasing physical activity, thereby helping residents maintain a healthy weight,465,466 reducing the urban heat island effect,467 and reducing exposure to harmful air pollutants from vehicles. Reducing the urban heat island effect also reduces energy demand and risks of power outages, which can contribute to health risks, such as patients losing access to electricity-dependent medical devices.
Climate change may weigh heavily on mental health in the general population and those already struggling with mental health disorders.468,469,470,471,472 One impact of rising temperatures, especially in combination with environmental and socioeconomic stresses, is violence towards others and towards self.473,474,475 Slow-moving disasters, such as drought, may affect mental health over many years.470 Studies of chronic stress indicate a potentially diminished ability to cope with subsequent exposures to stress.476,477,478
Populations under chronic social and economic stresses in urban and rural areas possess lower psychological, physical, and economic resilience (Ch. 10: Ag & Rural, KM 3). Communities that rely especially on well-functioning natural and agricultural systems in specific locations may be especially vulnerable to mental health effects when those systems fail. In the Southwest, the loss of stability and certainty in natural systems may affect physical, mental, and spiritual health of Indigenous peoples with close ties to the land.42,316 For example, extended drought raises concerns about maintaining Navajo Nation water-based ceremonies essential for spiritual health, livelihoods, cultural values, and overall well-being.301