finding 6.2 : exposure-risk-from-extreme-precipitation-events

Runoff from more frequent and intense extreme precipitation events will increasingly compromise recreational waters, shellfish harvesting waters, and sources of drinking water through increased introduction of pathogens and prevalence of toxic algal blooms [High Confidence]. As a result, the risk of human exposure to agents of water-related illness will increase [Medium Confidence].



This finding is from chapter 6 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 by 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, see Appendices 2 and 3.

Many water-related illnesses are of critical importance globally, such as cholera and hepatitis E virus, and they affect U.S. interests abroad, but the focus of this chapter is to address climate impacts on water-related illnesses of primary importance to human health within the United States. In addition, although climate change has the potential to impact national as well as global seafood supplies, this chapter does not cover these types of impacts because the peer-reviewed literature is not yet robust enough to make connections to human health outcomes in the United States. Even with those constraints, the impacts of climate on water-related illness are regionally or locally specific and may include increased risks as well as benefits. For example, the projected geographic range shifts of some Gambieridiscus species to more northern latitudes may mean that dominant ciguatera fish poisoning toxins enter the marine food web through different species, with increases of toxins in new areas where waters are warming and potential decreases in areas such as the Yucatan and eastern Caribbean Sea.1dfd14e0-eae8-46d9-9c3e-0fa3f0c37da4

Description of evidence base: Extreme precipitation can mobilize pathogens, nutrients, and chemical contaminants from agricultural, wildlife, and urban sources. Waterborne illness and outbreaks from pathogens following heavy precipitation events have been well documented in multiple studies using both passive and active surveillance on a local and regional level.dba82efa-be61-4edd-af85-ee5e3ed07139 686b4c04-41ae-4e4f-b66d-c091a81fbf2b b2f32879-6a7c-4f28-b53e-4e04a8aa0b1e 21e1cee8-0687-41e3-89f0-b6ccf4321f40 75de5138-1833-4aaa-8c2b-646287f3d33c 3e64a90d-f0c2-4f1a-a286-ce437bd95e60 0753011f-53bd-40b8-a4b9-f22040fe617f 662c61dc-9cc8-44ac-b867-053086299e68 74c63f7c-61a8-4f16-8107-302340e75bac Likewise, extreme precipitation events and subsequent increases in runoff are key climate factors that increase nutrient loading in freshwater and marine recreational waters, shellfish harvesting waters, and sources of drinking water, which in turn increases the likelihood of harmful cyanobacterial blooms that produce algal toxins.9224c0ef-9655-4335-a810-ce86baf5a502 The drinking water treatment process can remove cyanobacterial blooms; however, efficacy of the treatment processes may vary from 60% to 99.9%. Ineffective treatment could compromise water quality and may lead to severe treatment disruption or treatment plant shutdown.04e8c401-42e8-4f96-a1fc-98fcf05e240c 05f2b7a8-ce88-4e38-b426-917720b9c324 ef7ca73d-ff36-45d1-acfb-6941b4072a58 9224c0ef-9655-4335-a810-ce86baf5a502 More frequent and intense extreme precipitation events are projected for many regions in the United States as climate changes. Consistent, high-quality evidence from multiple studies supports a finding that increased runoff and flooding events are expected to increase contamination of source waters (for drinking water supply) and surface waters used for recreation, which may increase people’s exposure to pathogens and algal toxins that cause illness.030e3539-a620-441c-adb6-042db1a3fa6e 8c50c794-b09b-4215-b46c-6c24931faf6e 067c087d-ac72-448f-8a8f-c554d7897519 f60a6281-fa30-444d-9acd-0d132a6d1683 446ef7fa-5acc-45df-9247-b042fc1fac39 a7f52e54-2ce0-46fc-b0a2-60729757a8c0 a815bd0f-e3a7-4090-a35e-2f12381d9428 123e376c-79da-456f-96da-773e6f1e76ca 67a32928-4a0c-487d-9cd8-f442e47cb8ae 812fc19e-0fb3-4740-a4c7-bfef0e560666 3e34582d-ee92-45b3-9240-924ca5e98824 d4066a1c-799d-4b50-948b-ae6b71e19ad5 e4ad4655-b747-4844-9737-ee6da2650b39 603e74e7-cfae-45ff-bf78-4c38f32aa678 Other factors may modify these risks, such as increased air or water temperatures, residence time in the environment, lower water levels, or dilution.

New information and remaining uncertainties: Changes in exposure and risk are attributable to many factors in addition to climate. While extreme precipitation and flooding events introduce contaminants and pathogens to water to varying degrees depending on the characteristics of each individual event, they may not always result in increases in exposure due to planning and adaptive actions. There are limited studies on actual projections for changes in illness rates due to increasing frequency or intensity of extreme precipitation events. Uncertainty remains regarding appropriate methods for projecting changes in illness rates, including how to integrate considerations of human behavior into modeling (current methods to assess exposure risk assume similar human behavior across time scales and geography). Methodological challenges are related to 1) baseline case reporting issues (underreporting and underdiagnosis), 2) accounting for the effects of potential adaptation strategies/public health interventions (for example, public service announcements about how to avoid exposure), and 3) accounting for changes in public healthcare infrastructure and access that can reduce the risk of exposure or of illness/death.

Assessment of confidence based on evidence: Based on the evidence, there is high confidence that increasing frequency or intensity of extreme precipitation events will compromise recreational waters and sources of drinking water with pathogens, nutrients, and chemical contaminants from agricultural, wildlife, and urban sources.

There is consistent qualitative evidence that flooding associated with extreme precipitation events and storm surge results in loading of pathogens and nutrients to surface and groundwater (and drinking water distribution systems) through stormwater runoff and sewage overflows. However, other human and social factors modify risk, and there are no national-level studies upon which to draw conclusions regarding quantitative projections of increased exposure. Thus, the limited number of studies supports a medium confidence level that human exposure risk will increase due to changes in extreme events.

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