Health impacts associated with climate-related changes in exposure to extreme events include death, injury, or illness; exacerbation of underlying medical conditions; and adverse effects on mental health [High Confidence]. Climate change will increase exposure risk in some regions of the United States due to projected increases in the frequency and/or intensity of drought, wildfires, and flooding related to extreme precipitation and hurricanes [Medium Confidence].

This finding is from chapter 4 of The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment.

Process for developing key messages: The chapter was developed through technical discussions of relevant evidence and expert deliberation of the report authors at several workshops, teleconferences, and email exchanges. Authors considered inputs and comments submitted by the public, the National Academies of Sciences, and Federal agencies. For additional information on the overall report process, please see Appendices 2-3.

The health outcomes selected and prioritized for the chapter were based primarily on those that had substantial peer-reviewed literature to support statements. While many connections between changes in extreme events due to climate change and human health impacts appear intuitive, in some cases there may not be a robust body of peer-reviewed literature to support statements about direct effects. For example, while it is believed that droughts have the ability to impact water quality, which could in turn impact health, there are few studies documenting specific health consequences in the United States.f60a6281-fa30-444d-9acd-0d132a6d1683

In addition, due to space constraints, the authors did not intend to exhaustively identify all possible health impacts from every type of extreme event addressed in this chapter. Instead, the authors have provided an overview of possible impacts from different types of extreme events and provided a framework for understanding what additional factors (for example, population vulnerability, existing quality of infrastructure, etc.) can exacerbate or reduce adverse health outcomes.

Due to limited space and the uncertainty around future projections of tornadoes, we do not include detailed discussion of this topic in this chapter. We recognize that tornadoes can cause significant infrastructure damage and significant health impacts, and understanding how climate change will impact tornado intensity, frequency, and geographic distribution is an area of active scientific investigation.

Description of evidence base: The Third National Climate Assessment (2014 NCA) provides the most recent, peer-reviewed assessment conclusions for projected increases in the frequency and/or intensity of extreme precipitation, hurricanes, coastal inundation, drought, and wildfires in the United States.dd5b893d-4462-4bb3-9205-67b532919566 To the extent that these extreme events are projected to increase in some regions of the United States, people are expected to be at greater risk of exposure to health hazards.

Flooding associated with extreme precipitation, hurricanes, and coastal storms is expected to increase in some regions of the United States due to climate change, thereby increasing exposure to a variety of health hazards.3f2402c5-22aa-4f75-861e-f6aca127cd1f c4dc57e5-707f-4967-ab31-2b6e2b94fde5 61fd6e32-63d0-4f5a-bbbb-f68262376a37 The health impacts of floods and storms include death, injury, and illness; exacerbation of underlying medical conditions; and adverse effects on mental health.3be13957-eae2-4796-8504-ef2597b91b09 57f88e8c-2e4f-4e00-91e8-aea256ca3128 c43fa066-6d7b-481b-9a85-22da8c27243a aa29148e-c86c-443d-9c1d-5a1d7fbc3437 858d9e98-4217-4278-92bf-d113e5561c39 692dfb63-86b7-4268-be18-725585651b27 3a569dc6-4596-488a-8c30-c0b6f884677f 60be18ee-b5bc-4503-8f77-102561b193fb

Climate change is projected to lengthen or intensify droughts, especially in the Southwest,dd5b893d-4462-4bb3-9205-67b532919566 99baa64e-2877-4db9-b257-3f41149e73fe which may increase exposure to a broad set of health hazards.3f2402c5-22aa-4f75-861e-f6aca127cd1f 61fd6e32-63d0-4f5a-bbbb-f68262376a37 The potential health impacts of drought include: illness associated with reduced water quality and quantity f60a6281-fa30-444d-9acd-0d132a6d1683 54b0ebb2-d56b-4863-b32f-b8722abc2d32 6a9eaa35-c30c-4059-9b6b-331950df3f79 8c50c794-b09b-4215-b46c-6c24931faf6e b6607393-a0f4-47fb-8269-94bd378b6d61 and reduced air quality,792a6471-f6d3-4e85-bdb8-0e6efe9a24a9 eec73554-f1d8-4ab5-a618-c395429c086d ea9e8c20-fe7c-4a4e-b628-91ac3d300fb8 associations with increased rates of some infectious diseases,52d82168-d4c8-41b0-a318-501dcefb5ff8 6c4943e6-2a76-4989-b80e-8b4d9bacd78a c8b9489e-b737-4806-8685-4ebda89c8568 79d19ab8-4961-4f28-b678-78b213cdbdf3 f86c2421-ca6f-4634-822b-73de01b5168f and adverse mental health impacts.cd642a0a-9d8e-4c25-a56d-a64260553be6 9845a991-d58b-409b-91b9-670cc383d030 e24d8f4b-4c92-439c-ad81-c17bbbdfc682 dcb9ec60-0e20-442c-928e-cc47a25959bb c22caf01-8728-44cb-af5b-47fac06d1b68

Large, intense wildfires will occur more frequently in some regions of the United States, particularly in the western United States and Alaska,dd5b893d-4462-4bb3-9205-67b532919566 and this is expected to increase exposure to wildfire-related health risks.61fd6e32-63d0-4f5a-bbbb-f68262376a37 99baa64e-2877-4db9-b257-3f41149e73fe The health impacts of wildfire include death, injury, and illness,bc6db90e-3e83-4c12-8270-83da70318f67 35bb9e8b-e26b-4d68-85a3-c6fcbf8a7e6f 9cdc89b2-5f7e-4739-9bf6-788268921e03 d2b28363-411c-4444-9b05-8204ff607e36 a31388fc-07fd-4ca6-a6a4-7dc7b207e14a 8a6d6f43-acbf-4127-8912-10071eda9093 250b4ec3-1264-4570-8417-c00e6d8752a8 3f73c3f1-422d-44f0-8b31-889628464021 c8a01a08-ba4a-4d6c-af36-dd599317f471 4ee18e43-0d8d-4276-ad51-b87db1d8b7bc d0bcbc01-6c2e-48bb-a52c-dbd504505758 bf639de9-c45a-40d0-a115-5b1a5e45e5ee 107c077e-4d44-49d7-99a5-84a81f62b7e0 064a28ed-78a7-4e9c-b27f-052db874e800 a1fb85fd-306f-4b7a-8eb1-13925bc31f94 including exacerbation of underlying medical conditions.250b4ec3-1264-4570-8417-c00e6d8752a8 1a72beb2-f4a0-4db9-bac8-eac55cbf676d 47451452-d69e-4cd8-9565-7151ba299836

New information and remaining uncertainties: The role of climate change in observed shifts in and future projections of the frequency, intensity, geographic distribution, and duration of certain extreme events is an ongoing, active area of research. For example, although the 2014 NCAdd5b893d-4462-4bb3-9205-67b532919566 concluded that extreme events will increase in some regions of the United States, uncertainties remain with respect to projections of climate impacts at smaller, more local scales and the timing of such impacts (see Table 1). Climate change related projections of winter storms and severe storms, including tornadoes, hail, and thunderstorms, are still uncertain.

The human health implications of the changes in extreme events have not received as much research attention to date, and there are currently no published, national-scale, quantitative projections of changes in exposure risks for the four categories of extreme events addressed in this chapter. Relevant health surveillance and epidemiological data for extreme events are limited by underreporting, underestimation, and lack of a common definition of what constitutes an adverse health impact from an extreme event.91c3ced0-65bc-43f7-b50c-11742eb657d5 c43fa066-6d7b-481b-9a85-22da8c27243a For drought in particular, there are few studies documenting specific health consequences in the United States.f60a6281-fa30-444d-9acd-0d132a6d1683 Challenges to quantitatively estimating future human health risks for the four types of extreme events addressed in this chapter include limited data availability and lack of comprehensive modeling methods. For winter storms and severe storms especially, scientists need a better understanding of how climate change will affect future storm trends before they can make projections of future health impacts.

Assessment of confidence based on evidence: There is high confidence that the types of health impacts associated with climate-related changes in extremes include death, injury, or illness; exacerbation of underlying medical conditions; and adverse effects on mental health (see Table 1). Based on the evidence presented in the peer-reviewed literature, there is medium confidence regarding increases in exposure to health hazards associated with projected increases in the frequency and/or intensity of extreme precipitation, hurricanes, coastal inundation, drought, and wildfires in some regions of the United States.

Many qualitative studies have been published about the potential or expected health hazards from these events, but few draw strong or definitive conclusions that exposure to health hazards will increase due to climate change. Thus, the evidence is suggestive and supports a medium confidence level that, to the extent that these extreme events are projected to increase in some regions of the United States, people are expected to be at greater risk of exposure to health hazards. There is no quantitative information on which to base probability estimates of the likelihood of increasing exposure to health hazards associated with extreme precipitation, hurricanes, coastal inundation, drought, and wildfires.

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