Editing IPCC:AR6/WGII/Chapter-6 (section)

==== 6.2.4.6 Natural and Ecological Infrastructure ====

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Urban ecological infrastructure includes green (i.e., vegetated), blue (i.e., water-based) and grey (i.e., non-living) components of urban ecosystems (Li et al., 2017). While land cover change from urbanisation directly reduces the extent of natural and ecological infrastructure (e.g., Lin, Meyers and Barnett, 2015), notable risks arise from climate drivers. Recent research particularly highlights future climate impacts on coastal natural infrastructure, including beaches, wetlands and mangroves, which cause significant economic losses from property damage and decreasing tourism income, as well as loss of natural capital and ecosystem services. Research on climate risks to urban trees and forests is comparatively limited. Instead, urban vegetation and green infrastructure are most often cast as adaptation strategies to reduce urban heat, mitigate drought and provide other ecosystem benefits (see [[#6.3.2|Section 6.3.2]] ).

Coastal natural infrastructure is exposed to sea level rise, wave action and inundation from increasing storm events (See also Section CCP 2.2.1). Beaches, in particular, are highly exposed to climate-induced coastal erosion (Toimil et al., 2018; Section CCP2). Research from settlements across coastal Southern California, USA, show that 67% of all beaches may completely erode by 2100 (Vitousek, Barnard and Limber, 2017). Coastal zones across Cancún, Mexico, are exposed to a combination of sea level rise and tropical hurricanes, further exacerbated by urban development patterns blocking natural sediment replenishment to beaches (Escudero-Castillo et al., 2018). In another case, beach erosion along the heavily urbanised Valparaíso Bay, Chile, is heightened by El Niño Southern Oscillation (ENSO) events, which in the past have caused an additional 15–20 cm in mean sea level rise (Martínez et al., 2018).

Wetlands, mangroves and estuaries, which tend to be heavily urbanised areas, are highly at risk from sea level rise and changing precipitation (Green et al., 2017; Feller et al., 2017; [[#Alongi--2015|Alongi, 2015]] ; Osland et al., 2017; [[#Chow--2018|Chow, 2018]] ; [[#Godoy--2015|Godoy and Lacerda, 2015]] ). Sea level rise is a concern for wetlands and mangroves across coastal urban Asia, the Mississippi Delta (US) and low lying small island states (Ward et al., 2016b). Research on the highly urbanised Yangtze River estuary in China shows that soil submersion and erosion from sea level rise, compounded by land conversation to agriculture and urban development, will cause all tidal flats to disappear by 2100 (Wu, Zhou and Tian, 2017). In another example, sea level rise and high rates of tidal inundation have increased overall salinity in the San Francisco Bay-Delta estuary, threatening the ecosystem’s ability to support biodiversity ( [[#Parker--2019|Parker and Boyer, 2019]] ).

Research on climate risks to urban trees and forests highlight direct impacts from extreme temperatures, precipitation, wind events and sea level rise, as well as exposure to other hazards such as air pollution, fires, invasive species and disease ( [[#Ordóñez--2014|Ordóñez and Duinker, 2014]] ). Since the 1960s, climate change has enabled growth of urban trees, supported by longer growing seasons, higher atmospheric CO 2 concentrations and reduced diurnal temperature range (Pretzsch et al., 2017), as well as increased fertilisation through urban-enhanced nitrogen deposition (Decina, Hutyra and Templer, 2020). However, these trends may change in the future as further warming and decreasing water supply may depress tree fitness, thus enabling more pests ( [[#Dale--2017|Dale and Frank, 2017]] ).

Climate risks to urban natural and ecosystem infrastructure entail significant economic costs. For example, in 2012, Hurricane Sandy led to total losses of up to USD 6.5 million to the New York City region’s low-lying salt marshes and beaches ( [[#Meixler--2017|Meixler, 2017]] ). Research from coastal settlements across Catalonia, Spain, shows significant levels of tourism loss (which contribute to 11.1% of the region’s GDP), infrastructure damage and natural capital loss attributed to inundation and erosion of beaches, which are projected to retreat by −0.7 m yr −1 given current sea level rise projections of 0.53–1.75 m by 2100 (Jiménez et al., 2017).

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