Increases in some extreme weather events and storm surges will increase the risk that infrastructure for drinking water, wastewater, and stormwater will fail due to either damage or exceedance of system capacity, especially in areas with aging infrastructure [High Confidence]. As a result, the risk of exposure to water-related pathogens, chemicals, and algal toxins will increase in recreational and shellfish harvesting waters and in drinking water where treatment barriers break down [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: Water infrastructure in the United States is aging and may be inadequate or deteriorating. Combined sewers in many older cities were not designed to handle extreme precipitation events that are becoming more frequent with climate change. Multiple studies provide consistent, high-quality evidence that these systems are at risk of being overwhelmed during flood events or may be further damaged during other extreme weather events (e.g., storm surge), allowing contaminated surface water to run off into drinking water and recreational water sources.030e3539-a620-441c-adb6-042db1a3fa6e 8c50c794-b09b-4215-b46c-6c24931faf6e 067c087d-ac72-448f-8a8f-c554d7897519 f60a6281-fa30-444d-9acd-0d132a6d1683 123e376c-79da-456f-96da-773e6f1e76ca 812fc19e-0fb3-4740-a4c7-bfef0e560666 Drinking water source contamination may be exacerbated or insufficiently addressed by treatment processes at the plant or the distribution system. Drinking water treatment plants may be challenged by high pathogen loads and toxic cyanobacterial bloom events.8c50c794-b09b-4215-b46c-6c24931faf6e ef7ca73d-ff36-45d1-acfb-6941b4072a58 9224c0ef-9655-4335-a810-ce86baf5a502 Multiple studies support a finding that climate change will place additional stresses on the capacity of drinking water treatment facilities and may increase the risk that water infrastructure, especially aging infrastructure, will fail through either damage or exceedance of system capacity.e51f35c4-b5ba-4e95-8090-582e2897754b f60a6281-fa30-444d-9acd-0d132a6d1683 19adfcfa-88e4-4728-9242-d9934063bb69 19d0c5a6-be45-4234-8d62-6d3eff596da5

New information and remaining uncertainties: The human health consequences of aging water infrastructure failure depend not only on the local and regional climate factors that contribute to damage or capacity challenges but also the nature of the system and the pressures on it, the population affected, and the timeliness and adequacy of the response—all of which are inherently local or regional factors. Due to the complicated local and regional specificity, there are no national projections of the human health impact of water infrastructure failure. 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, mitigating risk with improvements to current water and sewerage systems), and 3) accounting for changes in public healthcare infrastructure and access that can reduce the risk of exposure or of illness/death if exposed.

Assessment of confidence based on evidence: Based on the evidence found in the peer-reviewed literature, there is high confidence that the anticipated climate change related increases in some extreme weather events and in storm surge will increase the risk that water infrastructure for drinking water, wastewater, and stormwater will fail through either damage or exceedance of system capacity, with aging infrastructure being particularly vulnerable. Evidence shows contamination to or from these systems occurs with heavy precipitation and other extreme weather events. There is consistent qualitative evidence suggesting that projected climate change effects on extreme weather patterns—particularly extreme precipitation and storm surge—can adversely affect water infrastructure and lead to increased loading of pathogens, algal toxins, and contaminants. However, 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 regarding risk of exposure.

References :

• Climate Change and Waterborne Disease Risk in the Great Lakes Region of the U.S. (030e3539)
• Extreme water-related weather events and waterborne disease (067c087d)
• generic Effect of climate change on sewer overflows in Milwaukee (123e376c)
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