Editing IPCC:AR6/WGII/Chapter-14 (section)

==== 14.5.3.1 Observed Impacts ====

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North American water resources continue to be affected by ongoing warming, with impacts driven by reductions in snow and ice, increases in extreme precipitation and hotter droughts ( ''high confidence'' ) ( [[#14.2|Section 14.2]] ; [[#Fleming--2014|Fleming and Dahlke, 2014]] ; [[#Mortsch--2015|Mortsch et al., 2015]] ; [[#Dudley--2017|Dudley et al., 2017]] ; [[#Fyfe--2017|Fyfe et al., 2017]] ; [[#McCabe--2017|McCabe et al., 2017]] ; [[#Chavarria--2018|Chavarria and Gutzler, 2018]] ; [[#Lall--2018|Lall et al., 2018]] ; [[#Bonsal--2019|Bonsal et al., 2019]] ; [[#USGCRP--2019|USGCRP, 2019]] ). The cascading effects of severe droughts, floods, sediment mobilisation, HABs and pathogen contamination episodes have revealed the vulnerability and exposure of large numbers of people and economic activities to those hazards.

North America’s dams, levees, wastewater-management and water conveyance facilities have improved water supply safety and have reduced flood and drought risks, but a substantial portion of that infrastructure is ageing and inadequate for modern conditions ( [[#Ho--2017|Ho et al., 2017]] ; [[#Tellman--2018|Tellman et al., 2018]] ; [[#Carlisle--2019|Carlisle et al., 2019]] ; [[#FEMA--2019|FEMA, 2019]] ; [[#ASCE--2021|ASCE, 2021]] ). Increasingly heavy precipitation from a variety of storm types has affected parts of North America ( [[#Feng--2016|Feng et al., 2016]] ; [[#Prein--2017a|Prein et al., 2017a]] ; [[#Kunkel--2019|Kunkel and Champion, 2019]] ; [[#Kunkel--2020|Kunkel et al., 2020]] ), contributing to contamination from combined sewer overflows ( [[#Olds--2018|Olds et al., 2018]] ) and increased flood damages that are partially attributed to anthropogenic climate change ( [[#van%20der%20Wiel--2017|van der Wiel et al., 2017]] ; Davenport, 2021). Extreme precipitation events have overwhelmed water control infrastructure, imperilling public safety and contributing to extensive damages in parts of North America ( [[#Kytomaa--2019|Kytomaa et al., 2019]] ; [[#Vano--2019|Vano et al., 2019]] ; [[#White--2019|White et al., 2019]] ). Damages stem from extremity of the event and prior land-use and infrastructure decisions ( ''high confidence'' ) ''.''

In South Carolina, 5 days of heavy rainfall in October 2015 caused the failure of more than 50 dams and some levees, significantly magnifying destruction from the floodwaters ( [[#FEMA--2016|FEMA, 2016]] ). Slow-moving, destructive storms like hurricanes Harvey (2017) and Florence (2018) have caused significant flooding ( [[#van%20Oldenborgh--2017|van Oldenborgh et al., 2017]] ; [[#Paul--2019b|Paul et al., 2019b]] ). In those cases, urban sprawl may have altered storm dynamics ( [[#Zhang--2018b|Zhang et al., 2018b]] ), while increased asset exposure to the flood hazard amplified the multi-billion-dollar losses ( [[#Klotzbach--2018|Klotzbach et al., 2018]] ; [[#Trenberth--2018|Trenberth et al., 2018]] ). A substantial fraction of the damage from hurricane Harvey’s extreme rainfall has been attributed to anthropogenic climate change (see Box 14.5; [[#Emanuel--2017|Emanuel, 2017]] ; [[#Risser--2017|Risser and Wehner, 2017]] ). A near disaster at California’s Oroville dam in 2017 was caused by inadequate infrastructure design and maintenance together with an unusually large number of atmospheric river (AR) storms. The event required emergency reservoir spills while the state was beginning recovery from the extreme 2012–2016 drought ( [[#Vano--2019|Vano et al., 2019]] ; [[#White--2019|White et al., 2019]] ).

In Mexico, some poor neighbourhoods and informal settlements are located in areas exposed to recurrent flooding. Residents often lack access to public services and technical resources for risk reduction, which heightens their vulnerability ( [[#Castro--2019|Castro and De Robles, 2019]] ).

Population growth and urban development have increased the exposure and vulnerability of Canadian communities to flood damages, with cumulative damages (including uninsured losses) exceeding 10 billion USD in the past decade ( [[#The%20Geneva%20Association--2020|The Geneva Association et al., 2020]] ). Recurring floods are particularly costly (e.g., New Brunswick) ( [[#Beltaos--2015|Beltaos and Burrell, 2015]] ; [[#Kovachis--2017|Kovachis et al., 2017]] ). Floods in High River, AB (2013) and Gatineau, QC (2017, 2019) initiated considerations of building flood resilience including planned retreat ( [[#Saunders-Hastings--2020|Saunders-Hastings et al., 2020]] ).

Extended and severe droughts in the western USA, northern Mexico and Canadian Prairies, exacerbated by higher temperatures, have caused economic and environmental damage ( [[#Williams--2013|Williams et al., 2013]] ; Agha Kouchak et al., 2015; [[#Diaz--2016|Diaz et al., 2016]] ; [[#Bain--2018|Bain and Acker, 2018]] ; [[#Lopez-Perez--2018|Lopez-Perez et al., 2018]] ; [[#Ortega-Gaucin--2018|Ortega-Gaucin et al., 2018]] ; [[#Xiao--2018|Xiao et al., 2018]] ; [[#Martinez-Austria--2019|Martinez-Austria et al., 2019]] ; [[#Bonsal--2020|Bonsal et al., 2020]] ; [[#Martin--2020b|Martin et al., 2020b]] ; [[#Milly--2020|Milly and Dunne, 2020]] ; [[#Overpeck--2020|Overpeck and Udall, 2020]] ). Droughts have intensified tensions among competing water-use interests and accelerated depletion of groundwater resources ( ''high confidence'' ) ( [[#14.5.4|Section 14.5.4]] ; [[#Pauloo--2020|Pauloo et al., 2020]] ).

Climate trends are affecting riverine, lake and reservoir water quality ( ''medium confidence'' ). Droughts and increased evapotranspiration have impaired water quality by concentrating pollutants in diminished water volumes ( [[#Paul--2019a|Paul et al., 2019a]] ). Cyanobacterial blooms and pathogen exposure events are increasing in frequency, intensity and duration in North America ( [[#Taranu--2015|Taranu et al., 2015]] ). They are closely associated with observed changes in precipitation intensity and associated nutrient loading (e.g., agricultural runoff, sanitary sewer overflows), elevated water temperatures and eutrophication ( [[#Michalak--2013|Michalak et al., 2013]] ; [[#Michalak--2016|Michalak, 2016]] ; [[#Trtanj--2016|Trtanj et al., 2016]] ; [[#Chapra--2017|Chapra et al., 2017]] ; [[#IBWC--2017|IBWC, 2017]] ; [[#Williamson--2017|Williamson et al., 2017]] ; [[#Olds--2018|Olds et al., 2018]] ; [[#Coffey--2019|Coffey et al., 2019]] ). These events endanger human and animal health, recreational and drinking water uses and aquatic ecosystem functioning, and cause economic losses ( [[#Michalak--2013|Michalak et al., 2013]] ; [[#Bullerjahn--2016|Bullerjahn et al., 2016]] ; [[#Chapra--2017|Chapra et al., 2017]] ; [[#Huisman--2018|Huisman et al., 2018]] ). Households and communities dependent on substandard wells, unimproved water sources or deficient water provision systems are more exposed than others to experience climate-related impairment of drinking water quality ( [[#14.5.6.5|Section 14.5.6.5]] ; [[#Allaire--2018|Allaire et al., 2018]] ; [[#Baeza--2018|Baeza et al., 2018]] ; [[#California%20State%20Water%20Resources%20Control%20Board--2021|California State Water Resources Control Board, 2021]] ; [[#Navarro-Espinoza--2021|Navarro-Espinoza et al., 2021]] ; Water and Tribes Initiative, 2021).

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