Editing IPCC:AR6/SROCC/Chapter-4 (section)

=== 4.3.3 Observed Impacts, and Current and Future Risk of Sea Level Rise ===

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SLR leads to hazards and impacts that are also partly inherent in other processes such as starvation of sediments provided by rivers (Kondolf et al., 2014); permafrost thaw and ice retreat; or the disruption of natural dynamics by land reclamation or sediment mining. Six main concerns for low-lying coasts (Figure 4.13) are: (i) permanent submergence of land by mean sea levels or mean high tides; (ii) more frequent or intense flooding; (iii) enhanced erosion; (iv) loss and change of ecosystems; (v) salinisation of soils, ground and surface water; and (vi) impeded drainage. This section discusses some of these hazards (flooding, erosion, salinisation) as well as observed and projected impacts on some critical marine ecosystems (marshes, mangroves, lagoons, coral reefs and seagrasses), ecosystem services (coastal protection) and human societies (people, assets, infrastructures, economic and subsistence activities, inequity and well-being, etc.). In many cases, the Chapter 4 assessment of impacts and responses uses results from literature based on values of SLR and ESL events prior to SROCC. However, the general findings reported here also carry forward with the new SROCC SLR and ESL values. Except in the case of submergence and flooding of coastal areas (Section 4.3.3.2), this section assumes no major additional adaptation efforts compared to today (i.e., neither significant intensification of ongoing action nor new types of action), thus reflecting the state of knowledge in the literature.

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'''Figure 4.13 | Overview of the main cascading effects of sea level rise (SLR). Styles and colours of lines (left hand side: light/dark blue; right hand side: dotted/non dotted and orange/green/dark yellow/purple/turquoise) and boxes are used only for the readability of the figure. Sea level hazards are discussed in Section 4.2. The various impacts listed […]'''
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Figure 4.13 | Overview of the main cascading effects of sea level rise (SLR). Styles and colours of lines (left hand side: light/dark blue; right hand side: dotted/non dotted and orange/green/dark yellow/purple/turquoise) and boxes are used only for the readability of the figure. Sea level hazards are discussed in Section 4.2. The various impacts listed in this figure are discussed in the sections below: Submergence of land and enhanced flooding (4.3.3.2); Erosion of land and beaches (4.3.3.3); Salinisation (4.3.3.4); Loss of and changes in ecosystems (4.3.3.5); Loss of land and land uses (4.3.3.2); Loss of ecosystems services (4.3.3.5); Damage to people and to the built environment (4.3.3.2, 4.3.3.3, 4.3.3.4 and 4.3.3.6); Damages to human activities (4.3.3.6). Non-climate anthropogenic drivers are discussed in Section 4.3.2 and other climate-related drivers are notably discussed in Section 5.2.1 and 5.2.2.

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==== 4.3.3.1 Attribution of Observed Physical Changes to Sea Level Rise ====

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The AR5 concludes that attribution of coastal changes to SLR is difficult because ‘the coastal sea level change signal is often small when compared to other processes’ (Wong et al., 2014: 375). New literature, however, shows that extreme water levels at the coast are rising due to mean SLR (4.2.2.4 for observations, and 4.3.5 for projections), with observable impacts on chronic flooding in some regions (Sweet and Park, 2014; Strauss et al., 2016).

On coastal morphological changes for example, contemporary SLR currently acts as a ‘background driver’, with extreme events, changes in wave patterns, tides and human intervention often described as the prevailing drivers of observed changes (Grady et al., 2013; Albert et al., 2016). Morphological changes are also interacting with other impacts of SLR, such as coastal flooding (Pollard et al., 2018). Despite the complexity of the attribution issue (Romine et al., 2013; Le Cozannet et al., 2014), recent literature suggests possibly emerging signs of the direct influence of recent SLR on shoreline behaviour, for example on small highly-sensitive reef islands in New Caledonia (Garcin et al., 2016) and in the Solomon Islands (Albert et al., 2016). Early signs of the direct influence of SLR on estuaries’ water salinity are also emerging, for example, in the Delaware, USA, where Ross et al. (2015) estimate a rate of salinity increase by as much as 4.4 psu (Practical Salinity Unit) per metre of SLR since the 1950s.

Overall, while the literature suggests that it is still too early to attribute coastal impacts to SLR in most of the world’s coastal areas, there is ''very high confidence'' that as sea level continues to rise (Sections 4.2.3.2, 4.2.3.3), the frequency, severity and duration of hazards and related impacts increases (Woodruff et al., 2013; Lilai et al., 2016; Vitousek et al., 2017; Sections 4.2.3.4, 6.3.1.3). Detectable impacts and attributable impacts on shoreline behaviour are expected as soon as the second half of the 21st century (Nicholls and Cazenave, 2010; Storlazzi et al., 2018).

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==== 4.3.3.2 Submergence and Flooding of Coastal Areas ====

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Since AR5, a number of continental and global scale coastal exposure studies have accounted for sub-national human dynamics such as coastward migration or coastal urbanisation. These studies project a population increase in the LECZ (coastal areas below 10 m of elevation) by 2100 of 85 to 239 million people as compared to only considering national dynamics (Merkens et al., 2016 <sup>[[#fn:r1176|1176]]</sup> ; Section 4.3.2). Under the five SSPs and without SLR, the population living in the LECZ increases from 640–700 million in 2000 to over one billion in 2050 under all SSPs, and then declines to 500–900 million in 2100 under all SSPs, except for SSP3 (i.e., a world in which countries will increasingly focus on domestic issues, or at best regional ones), for which the coastal population reaches 1.1–1.2 billion (Jones and O’Neill, 2016 <sup>[[#fn:r1177|1177]]</sup> ; Merkens et al., 2016 <sup>[[#fn:r1178|1178]]</sup> ).

The population exposed to mean and ESL events will grow significantly during the 21st century (high confidence) with socioeconomic development and SLR contributing roughly equally (medium confidence). Considering an average relative SLR of 0.7–0.9 m but no population growth, the number of people living below the hundred-year ESL in Latin America and the Caribbean will increase from 7.5 million in 2011 to 9 million by the end of the century (Reguero et al., 2015 <sup>[[#fn:r1179|1179]]</sup> ). Considering population growth and urbanisation, only 21 cm of global mean SLR by 2060 would increase the global population living below the hundred-year ESL from about 189 million in 2000 to 316–411 million in 2060, with the largest absolute changes in South and Southeast Asia and the largest relative changes in Africa (Neumann et al., 2015 <sup>[[#fn:r1180|1180]]</sup> ). Considering population growth, Hauer et al. (2016) <sup>[[#fn:r1181|1181]]</sup> estimate that 4.3 and 13.1 million people in the USA would live below the levels of 0.9 and 1.8 m SLR by 2100.

New coastal flood risk studies conducted since AR4 at global, continental and city scale, reinforce AR5 findings that if coastal societies do not adapt, flood risks will increase by 2–3 orders of magnitude reaching catastrophic levels by the end of the century, even under the lower end SLR expected under RCP2.6 (high confidence; Hinkel et al., 2014 <sup>[[#fn:r1182|1182]]</sup> ; Abadie et al., 2016 <sup>[[#fn:r1183|1183]]</sup> ; Diaz, 2016 <sup>[[#fn:r1184|1184]]</sup> ; Hunter et al., 2017 <sup>[[#fn:r1185|1185]]</sup> ; Lincke and Hinkel, 2018 <sup>[[#fn:r1186|1186]]</sup> ; Abadie, 2018 <sup>[[#fn:r1187|1187]]</sup> ; Brown et al., 2018a <sup>[[#fn:r1188|1188]]</sup> ; Nicholls, 2018 <sup>[[#fn:r1189|1189]]</sup> ). In combination, these studies take into account a SLR scenario range wider than the likely range of AR5 but consistent with the range of projections assessed in this report (Section 4.2.3.2). For example, considering 25–123 cm of SLR in 2100, all SSPs and no adaptation, Hinkel et al. (2014) find that 0.2–4.6% of global population is expected to be flooded annually in 2100, with expected annual damages (EAD) amounting to 0.3–9.3% of global GDP. Assessing 120 cities globally, Abadie (2018) find that under a weighted combination of the probabilistic scenarios, New Orleans and Guangzhou Guangdong rank highest with EAD above 1 trillion USD (not discounted) in each city. For Europe, EAD are expected to rise from 1.25 billion EUR today to 93–960 billion EUR by the end of the century (Vousdoukas et al., 2018b <sup>[[#fn:r1190|1190]]</sup> ). Already today, many small islands face large flood damages relative to their GDP specifically through TCs (Cashman and Nagdee, 2017 <sup>[[#fn:r1191|1191]]</sup> ) and under SLR EAD can reach up to several percent of GDP in 2100, as highlighted in AR5 (Wong et al., 2014 <sup>[[#fn:r1192|1192]]</sup> ). Similar to the exposure studies, estimates of future flood risk without considering adaptation, as presented in this paragraph, do not provide a meaningful characterisation of coastal flood risks, because adaptation and specifically hard protection is expected to be widespread during the 21st century in urban areas and cities (high confidence; Section 4.4.3.2.2). Rather, these estimates need to be seen as illustrations of the scale of adaptation needed to offset risk.

Flood risk studies that have included adaptation find that hard coastal protection is generally very effective in reducing flood risks during the 21st century even under high SLR scenarios (high confidence; Hinkel et al., 2014 <sup>[[#fn:r1193|1193]]</sup> ; Diaz, 2016 <sup>[[#fn:r1194|1194]]</sup> ; Brown et al., 2018a <sup>[[#fn:r1195|1195]]</sup> ; Hinkel et al., 2018 <sup>[[#fn:r1196|1196]]</sup> ; Lincke and Hinkel, 2018 <sup>[[#fn:r1197|1197]]</sup> ; Tamura et al., 2019 <sup>[[#fn:r1198|1198]]</sup> ) (Section 4.4.2.2.2). For example, Hinkel et al. (2014) find that under 25–123 cm of SLR in 2100 and all SSPs, hard coastal protection reduces the annual number of people affected by coastal floods and EAD by 2–3 orders of magnitude. Under high-end SLR and beyond the 21st century, effectiveness of coastal adaptation is expected to decline rapidly, but there is a lack of studies addressing this issue. Furthermore, there is a lack of studies taking into account responses beyond hard protection such as ecosystem-based adaptation, accommodation, advance and retreat (Sections 4.4.2).

Studies also confirm AR5 findings that the relative costs and benefits of coastal adaptation are distributed unequally across countries and regions (high confidence; Wong et al., 2014 <sup>[[#fn:r1199|1199]]</sup> ; Diaz, 2016 <sup>[[#fn:r1200|1200]]</sup> ; Lincke and Hinkel, 2018 <sup>[[#fn:r1201|1201]]</sup> ; Tamura et al., 2019 <sup>[[#fn:r1202|1202]]</sup> ). For example, while the median cost of protection and retreat under RCP8.5 in 2050 has been estimated to be under 0.09% of national GDP, large relative costs are found for small island states such as the Marshall Islands (7.6%), the Maldives (7.5%), Tuvalu (4.6%) and Kiribati (4.1%; Diaz, 2016 <sup>[[#fn:r1203|1203]]</sup> ). Furthermore, on a global average and for urban and densely populated regions, hard protection is highly cost efficient with benefit-cost ratios up to 104, but for poorer and less densely populated areas benefit-cost ratios are generally smaller than one (Lincke and Hinkel, 2018 <sup>[[#fn:r1204|1204]]</sup> ). Hence, without substantial transfer payments supporting poor areas, coastal flood risks will evolve unequally during this century, with richer and densely populated areas well protected behind hard structures and poorer less densely populated areas suffering losses and damages, and eventually retreating from the coast.

While continental to global scale flood exposure and risk studies have also explored a wider range of uncertainty as compared to AR5, much remains to be done. All of these studies rely on global elevation data, but few studies have explored the underlying bias. For example, for the Po delta in Italy, it was found that elevation data based on the widely used Shuttle Radar Topography Mission (SRTM), Reuter et al. (2007) overestimates the 100-year floodplain by about 50% as compared to local Lidar data (Wolff et al., 2016 <sup>[[#fn:r1205|1205]]</sup> ), while in the Ria Formosa region in Portugal SRTM underestimates EAD by up to 50% depending on the resampled resolution of the Lidar data (Vousdoukas et al., 2018a <sup>[[#fn:r1206|1206]]</sup> ). For the USA, SRTM data systemically underestimates population exposure below 3 m by more than 60% as compared to coastal Lidar data (Kulp and Strauss, 2016 <sup>[[#fn:r1207|1207]]</sup> ). A global scale comparison of major contributors to flood risk uncertainty finds that uncertainty in digital elevation data is roughly at equal footing with uncertainties in socioeconomic development, emission scenarios, and SLR in determining the magnitude of flood risks in the 21st century (Hinkel et al., 2014 <sup>[[#fn:r1208|1208]]</sup> ). At a European level, the number of people living in the 100-year coastal floodplain can vary between 20–70% depending on the different inundation models used and the inclusion or exclusion of wave set up (Vousdoukas, 2016 <sup>[[#fn:r1209|1209]]</sup> ). Comparing damage functions attained in different studies for European cities, Prahl et al. (2018 <sup>[[#fn:r1210|1210]]</sup> ) find up to four-fold differences in damages for floods above 3 m. Another major source of uncertainty relates to uncertainties in present-day ESL events due to the application of different extreme value methods (Wahl et al., 2017 <sup>[[#fn:r1211|1211]]</sup> ; Section 4.2.3.4). While all of the uncertainties reported above affected the actual size of exposure and flood risk figures, they do not affect the overall conclusions drawn here.

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==== 4.3.3.3 Coastal Erosion and Projected Global Impacts of Enhanced Erosion on Human Systems ====

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Recent global assessments of coastal erosion indicate that land losses currently dominate over land gains and that human interventions are a major driver of shoreline changes (Cazenave and Cozannet, 2014 <sup>[[#fn:r1212|1212]]</sup> ; Luijendijk et al., 2018 <sup>[[#fn:r1213|1213]]</sup> ; Mentaschi et al., 2018 <sup>[[#fn:r1214|1214]]</sup> ). Luijendijk et al. (2018) <sup>[[#fn:r1215|1215]]</sup> estimate that over the 1984–2016 period, about a quarter of the world’s sandy beaches eroded at rates exceeding 0.5m yr–1 while about 28% accreted. While such global results can be challenged due to the relatively large detection threshold used (±0.5 m yr–1), there is growing literature indicating that coastal erosion is occurring or increasing, e.g. in the Arctic (Barnhart et al., 2014a <sup>[[#fn:r1216|1216]]</sup> ; Farquharson et al., 2018 <sup>[[#fn:r1217|1217]]</sup> ; Irrgang et al., 2019 <sup>[[#fn:r1218|1218]]</sup> ), Brazil (Amaro et al., 2015 <sup>[[#fn:r1219|1219]]</sup> ), China (Yang et al., 2017 <sup>[[#fn:r1220|1220]]</sup> ), Colombia (Rangel-Buitrago et al., 2015 <sup>[[#fn:r1221|1221]]</sup> ), India (Kankara et al., 2018 <sup>[[#fn:r1222|1222]]</sup> ), and along a large number of deltaic systems worldwide (e.g., Section 4.2.2.4).

Since AR5, however, there is growing appreciation and understanding of the ability of coastal systems to respond dynamically to SLR (Passeri et al., 2015 <sup>[[#fn:r1223|1223]]</sup> ; Lentz et al., 2016 <sup>[[#fn:r1224|1224]]</sup> ; Deng et al., 2017 <sup>[[#fn:r1225|1225]]</sup> ). Most low-lying coastal systems exhibit important feedbacks between biological and physical processes (e.g., Wright and Nichols, 2018), that have allowed them to maintain a relatively stable morphology under moderate rates of SLR (&lt;0.3 cm yr–1) over the past few millennia (Woodruff et al., 2013 <sup>[[#fn:r1226|1226]]</sup> ; Cross-Chapter Box 5 in Chapter 1). In a global review on multi-decadal changes in the land area of 709 atoll islands, Duvat (2019) <sup>[[#fn:r1227|1227]]</sup> shows that in a context of more rapid SLR than the global mean (Becker et al., 2012 <sup>[[#fn:r1228|1228]]</sup> ; Palanisamy et al., 2014 <sup>[[#fn:r1229|1229]]</sup> ), 73.1% of islands were stable in area, while respectively 15.5% and 11.4% increased and decreased in size. While anthropogenic drivers played a major role, especially in urban islands (e.g., shoreline stabilisation by coastal defences, increase in island size as a result of reclamation works), this study and others (e.g., McLean and Kench, 2015) suggest that these islands have had the capacity to maintain their land area by naturally adjusting to SLR over the past decades (high confidence). However, it has been argued that this capacity could be reduced in the coming decades, due to the combination of higher rates of SLR, increased wave energy (Albert et al., 2016 <sup>[[#fn:r1230|1230]]</sup> ), changes in run-up (Shope et al., 2017 <sup>[[#fn:r1231|1231]]</sup> ) and storm wave direction (Harley et al., 2017 <sup>[[#fn:r1232|1232]]</sup> ), effects of ocean warming and acidification on critical ecosystems such as coral reefs (Section 4.3.3.5.2), and a continued increase in anthropogenic pressure.

From a global scale perspective, based on AR4 SLR scenarios and without considering the potential benefits of adaptation, Hinkel et al. (2013b) estimate that about 6000 to 17,000 km2 of land is expected to be lost during the 21st century due to enhanced coastal erosion associated with SLR, in combination with other drivers. This could lead to a displacement of 1.6–5.3 million people and associated cumulative costs of 300 to 1000 billion USD (Section 4.4.3.5). Importantly, these global figures mask the wide diversity of local situations; and some literature is emerging on the non-physical and non-quantifiable impacts of coastal erosion, for example, on the loss of recreational grounds and the induced risks to the associated social dimensions (i.e., how local communities experience coastal erosion impacts; Karlsson et al., 2015 <sup>[[#fn:r1233|1233]]</sup> ).

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==== 4.3.3.4 Salinisation ====

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With rising sea levels, saline water intrusion into coastal aquifers and surface waters and soils is expected to be more frequent and enter farther landwards. Salinisation of groundwater, surface water and soil resources also increases with land-based drought events, decreasing river discharges in combination with water extraction and SLR ''(high confidence).''

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===== 4.3.3.4.1 Coastal aquifers and groundwater lenses =====

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Groundwater volumes will primarily be affected by variations in precipitation patterns (Taylor et al., 2013; Jiménez Cisneros et al., 2014), which are expected to increase water stress in small islands (Holding et al., 2016). While SLR will mostly impact groundwater quality (Bailey et al., 2016) and in turn exacerbate salinisation induced by marine flooding events (Gingerich et al., 2017), it will also affect the watertable height (Rotzoll and Fletcher, 2013; Jiménez Cisneros et al., 2014; Masterson et al., 2014; Werner et al., 2017). In addition, the natural migration of groundwater lenses inland in response to SLR can also be severely constrained by urbanisation, for example, in semi-arid South Texas, USA (Uddameri et al., 2014).

These changes will affect both freshwater availability (for drinking water supply and agriculture) and vegetation dynamics. At many locations, however, direct anthropogenic influences, such as groundwater pumping for agricultural or urban uses, already impact salinisation of coastal aquifers more strongly than what is expected from SLR in the 21st century (Ferguson and Gleeson, 2012; Jiménez Cisneros et al., 2014; Uddameri et al., 2014), with trade-offs in terms of groundwater depletion that may contribute to anthropogenic subsidence and thus increase coastal flood risk. Recent studies also suggest that the influence of land-surface inundation on seawater intrusion and resulting salinisation of groundwater lenses on small islands has been underestimated until now (Ataie-Ashtiani et al., 2013; Ketabchi et al., 2014). Such impacts will potentially also combine with a projected drying of most of the tropical-to-temperate islands by mid-century (Karnauskas et al., 2016).

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===== 4.3.3.4.2 Surface waters =====

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The quality of surface water resources (in estuaries, rivers, reservoirs, etc.) can be affected by the intrusion of saline water, both in a direct (increased salinity) and indirect way (altered environmental conditions which change the behaviour of pollutants and microbes). In terms of direct impacts, statistical models and long-term (1950 to present) records of salinity show significant upward trends in salinity and a positive correlation between rising sea levels and increasing residual salinity, for example in the Delaware Estuary, USA (Ross et al., 2015). Higher salinity levels, further inland, have also been reported in the Gorai river basin, southwestern Bangladesh (Bhuiyan and Dutta, 2012), and in the Mekong Delta, Vietnam. In the Mekong Delta for instance, salinity intrusion extends around 15 km inland during the rainy season and typically around 50 km during dry season (Gugliotta et al., 2017). Importantly, salinity intrusion in these deltas is caused by a variety of factors such as changes in discharge and water abstraction along with relative SLR. More broadly, the impact of salinity intrusion can be significant in river deltas or low-lying wetlands, especially during low-flow periods such as in the dry season (Dessu et al., 2018). In Bangladesh, for instance, some freshwater fish species are expected to lose their habitat with increasing salinity, with profound consequences on fish-dependent communities (Dasgupta et al., 2017). In the Florida Coastal Everglades, sea level increasingly exceeds ground surface elevation at the most downstream freshwater sites, affecting marine-to-freshwater hydrologic connectivity and transport of salinity and phosphorous upstream from the Gulf of Mexico. The impact of SLR is higher in the dry season when there is practically no freshwater inflow (Dessu et al., 2018). Salinity intrusion was shown to cause shifts in the diatom assemblages, with expected cascading effects through the food web (Mazzei and Gaiser, 2018). Salinisation of surface water may lead to limitations in drinking water supply (Wilbers et al., 2014), as well as to future fresh water shortage in reservoirs, for example in Shanghai (Li et al., 2015). Salinity changes the partitioning and mobility of some metals, and hence their concentration or speciation in the water bodies (Noh et al., 2013; Wong et al., 2015; de Souza Machado et al., 2018). Varying levels of salinity also influence the abundance and toxicity of ''Vibrio cholerae'' in the Ganges Delta (Batabyal et al., 2016).

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===== 4.3.3.4.3 Soils =====

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Salinisation is one of the major drivers of soil degradation, with sea water intrusion being one of the common causes (Daliakopoulos et al., 2016). In a study in the Ebro Delta, Spain, for instance, soil salinity was shown to be directly related to distances to the river, to the delta inner border, and to the old river mouth (Genua-Olmedo et al., 2016). Land elevation was the most important variable in explaining soil salinity.

SLR was also shown to decrease organic carbon (C <sub>org</sub> ) concentrations and stocks in sediments of salt marshes as reworked marine particles contribute with a lower amount of C <sub>org</sub> than terrigenous sediments. C <sub>org</sub> accumulation in tropical salt marshes can be as high as in mangroves and the reduction of C <sub>org</sub> stocks by ongoing SLR might cause high CO <sub>2</sub> releases (Ruiz-Fernández et al., 2018). In many cases attribution to SLR is missing, but, independent from clear attribution, sea water intrusion leads to a salinisation of exposed soils with changes in carbon dynamics (Ruiz-Fernández et al., 2018) and microbial communities (Sánchez-Rodríguez et al., 2017), soil enzyme activity and metal toxicity (Zheng et al., 2017). Water salinity levels in the pores of coastal marsh soils can become significantly elevated in just one week of flooding by sea water, which can potentially negatively impact associated microbial communities for significantly longer time periods (McKee et al., 2016). SLR will also alter the frequency and magnitude of wet/dry periods and salinity levels in coastal ecosystems, with consequences for the formation of climate relevant GHGs (Liu et al., 2017b) and therefore feedbacks to the climate.

Soil salinisation affects agriculture directly with impacts on plant germination (Sánchez-García et al., 2017), plant biomass (rice and cotton) production (Yao et al., 2015), and yield (Genua-Olmedo et al., 2016). Impact on agriculture is especially relevant in low-lying coastal areas where agricultural production is a major land use, such as in river deltas.

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==== 4.3.3.5 Ecosystems and Ecosystem Services ====

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===== 4.3.3.5.1 Tidal wetlands =====

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Global coastal wetlands have been reduced by a half since the pre-industrial period due to the impacts of both climatic and non-climatic drivers such as flooding, coastal urbanisation, alterations in drainage and sediment supply. (Sections 4.3.2.3, 5.3.2). Potentially one of the most important of the eco-morphodynamic feedback allowing for relatively stable morphology under SLR is the ability of marsh and mangrove systems to enhance the trapping of sediment, which in turn allows tidal wetlands to grow and increase the production and accumulaGlobal coastal wetlands have been reduced by a half since the pre-industrial period due to the impacts of both climatic and non-climatic drivers such as flooding, coastal urbanisation, alterations in drainage and sediment supply. (Sections 4.3.2.3, 5.3.2). Potentially one of the most important of the eco-morphodynamic feedbacks allowing for relatively stable morphology under SLR is the ability of marsh and mangrove systems to enhance the trapping of sediment, which in turn allows tidal wetlands to grow and increase the production and accumulation of organic material (Kirwan and Megonigal, 2013 <sup>[[#fn:r1272|1272]]</sup> ). When ecosystem health is maintained and sufficient sediment exists to support their growth, this particular feedback has generally allowed marshes and mangrove systems to build vertically at rates equal to or greater than SLR up to the present day (Kirwan et al., 2016 <sup>[[#fn:r1273|1273]]</sup> ; Woodroffe et al., 2016 <sup>[[#fn:r1274|1274]]</sup> ).

While recent reviews suggest that mangroves’ surface accretion rate will keep pace with a high SLR scenario (RCP8.5) up to years 2055 and 2070 in fringe and basin mangrove settings, respectively (Sasmito et al., 2016 <sup>[[#fn:r1275|1275]]</sup> ), process-based models of vertical marsh growth that incorporate biological and physical feedbacks support survival under rates of SLR as high as 1–5 cm yr–1 before drowning (Kirwan et al., 2016 <sup>[[#fn:r1276|1276]]</sup> ). Threshold rates of SLR before marsh drowning however vary significantly from site-to-site and can be substantially lower than 1 cm yr–1 in micro-tidal regions where the tidal trapping of sediment is reduced and/or in areas with low sediment availability (Lovelock et al., 2015 <sup>[[#fn:r1277|1277]]</sup> ; Ganju et al., 2017 <sup>[[#fn:r1278|1278]]</sup> ; Jankowski et al., 2017 <sup>[[#fn:r1279|1279]]</sup> ; Watson et al., 2017 <sup>[[#fn:r1280|1280]]</sup> ). Global environmental change may also to lead to changes in growth rates, productivity and geographic distribution of different mangrove and marsh species, including the replacement of environmentally sensitive species by those possessing greater climatic tolerance (Krauss et al., 2014 <sup>[[#fn:r1281|1281]]</sup> ; Reef and Lovelock, 2014 <sup>[[#fn:r1282|1282]]</sup> ; Coldren et al., 2019 <sup>[[#fn:r1283|1283]]</sup> ). Processes impacting lateral changes at the marsh boundary including wave erosion are just as important, if not more, than vertical accretion rates in determining coastal wetland survival (e.g., Mariotti and Carr, 2014). For most low-lying coastlines, a seaward loss of wetland area due to marsh retreat could be offset by a similar landward migration of coastal wetlands (Kirwan and Megonigal, 2013 <sup>[[#fn:r1284|1284]]</sup> ; Schile et al., 2014 <sup>[[#fn:r1285|1285]]</sup> ), this landward migration having the potential to maintain and even increase the extent of coastal wetlands globally (Morris et al., 2012 <sup>[[#fn:r1286|1286]]</sup> ; Kirwan et al., 2016 <sup>[[#fn:r1287|1287]]</sup> ; Schuerch et al., 2018 <sup>[[#fn:r1288|1288]]</sup> ). This natural process will however be constrained in areas with steep topography or hard engineering structures (i.e., coastal squeeze, Section 4.3.2.4). Seawalls, levees and dams can also prevent the fluvial and marine transport of sediment to wetland areas and reduce their resilience further (Giosan, 2014 <sup>[[#fn:r1289|1289]]</sup> ; Tessler et al., 2015 <sup>[[#fn:r1290|1290]]</sup> ; Day et al., 2016 <sup>[[#fn:r1291|1291]]</sup> ; Spencer et al., 2016 <sup>[[#fn:r1292|1292]]</sup> ). When ecosystem health is maintained and sufficient sediment exists to support their growth, this particular feedback has generally allowed marshes and mangrove systems to build vertically at rates While recent reviews suggest that mangroes’ surface accretion rate will keep pace with a high SLR scenario (RCP8.5) up to years 2055 and 2070 in fringe and basin mangrove settings, respectively (Sasmito et al., 2016 <sup>[[#fn:r1275|1275]]</sup> ), process-based models of vertical marsh growth that incorporate biological and physical feedbacks support survival under rates of SLR as high as 1–5 cm yr–1 before drowning (Kirwan et al., 2016 <sup>[[#fn:r1276|1276]]</sup> ). Threshold rates of SLR before marsh drowning however vary significantly from site-to-site and can be substantially lower than 1 cm yr–1 in micro-tidal regions where the tidal trapping of sediment is reduced and/or in areas with low sediment availability (Lovelock et al., 2015 <sup>[[#fn:r1277|1277]]</sup> ; Ganju et al., 2017 <sup>[[#fn:r1278|1278]]</sup> ; Jankowski et al., 2017 <sup>[[#fn:r1279|1279]]</sup> ; Watson et al., 2017 <sup>[[#fn:r1280|1280]]</sup> ). Global environmental change may also to lead to changes in growth rates, productivity and geographic distribution of different mangrove and marsh species, including the replacement of environmentally sensitive species by those possessing greater climatic tolerance (Krauss et al., 2014 <sup>[[#fn:r1281|1281]]</sup> ; Reef and Lovelock, 2014 <sup>[[#fn:r1282|1282]]</sup> ; Coldren et al., 2019 <sup>[[#fn:r1283|1283]]</sup> ). Processes impacting lateral changes at the marsh boundary including wave erosion are just as important, if not more, than vertical accretion rates in determining coastal wetland survival (e.g., Mariotti and Carr, 2014). For most low-lying coastlines, a seaward loss of wetland area due to marsh retreat could be offset by a similar landward migration of coastal wetlands (Kirwan and Megonigal, 2013 <sup>[[#fn:r1284|1284]]</sup> ; Schile et al., 2014 <sup>[[#fn:r1285|1285]]</sup> ), this landward migration having the potential to maintain and even increase the extent of coastal wetlands globally (Morris et al., 2012 <sup>[[#fn:r1286|1286]]</sup> ; Kirwan et al., 2016 <sup>[[#fn:r1287|1287]]</sup> ; Schuerch et al., 2018 <sup>[[#fn:r1288|1288]]</sup> ). This natural process will however be constrained in areas with steep topography or hard engineering structures (i.e., coastal squeeze, Section 4.3.2.4). Seawalls, levees and dams can also prevent the fluvial and marine transport of sediment to wetland areas and reduce their resilience further (Giosan, 2014 <sup>[[#fn:r1289|1289]]</sup> ; Tessler et al., 2015 <sup>[[#fn:r1290|1290]]</sup> ; Day et al., 2016 <sup>[[#fn:r1291|1291]]</sup> ; Spencer et al., 2016 <sup>[[#fn:r1292|1292]]</sup> ).

<div id="section-4-3-3-5ecosystems-and-ecosystem-services-block-4"></div>

<span id="coral-reefs"></span>
===== 4.3.3.5.2 Coral reefs =====

<div id="section-4-3-3-5ecosystems-and-ecosystem-services-block-5"></div>

Coral reefs are considered to be the marine ecosystem most threatened by climate-related ocean change, especially ocean warming and acidification, even under an RCP2.6 scenario (Gattuso et al., 2015 <sup>[[#fn:r1293|1293]]</sup> ; Albright et al., 2018 <sup>[[#fn:r1294|1294]]</sup> ; Hoegh-Guldberg et al., 2018 <sup>[[#fn:r1295|1295]]</sup> ; Díaz et al., 2019 <sup>[[#fn:r1296|1296]]</sup> ; Section 5.3.4). AR5 concluded that ‘a number of coral reefs could […] keep up with the maximum rate of SLR of 15.1 mm yr–1 projected for the end of the century […] (medium confidence) [but a future net accretion rate lower] than during the Holocene (Perry et al., 2013 <sup>[[#fn:r1297|1297]]</sup> ) and increased turbidity (Storlazzi et al., 2011 <sup>[[#fn:r1298|1298]]</sup> ) will weaken this capability (very high confidence)’ (Wong et al., 2014: 379 <sup>[[#fn:r1299|1299]]</sup> ). Subsequently, some studies suggested that SLR may have negligible impacts on coral reefs’ vertical growth because the projected rate and magnitude of SLR by 2100 are within the potential accretion rates of most coral reefs (van Woesik et al., 2015 <sup>[[#fn:r1300|1300]]</sup> ). Other studies, however, stressed that the overall net vertical accretion of reefs may decrease after the first 30 years of rise in a 1.2 m SLR scenario (Hamylton et al., 2014 <sup>[[#fn:r1301|1301]]</sup> ), and that most reefs will not be able to keep up with SLR under RCP4.5 and beyond (Perry et al., 2018 <sup>[[#fn:r1302|1302]]</sup> ). The SR1.5 also concludes that coral reefs ‘are projected to decline by a further 70–90% at 1.5°C (high confidence) with larger losses (&gt;99%) at 2°C (very high confidence)’ (Hoegh-Guldberg et al., 2018: 10 <sup>[[#fn:r1303|1303]]</sup> ). A key point is that SLR will not act in isolation of other drivers. Cumulative impacts, including anthropogenic drivers, are estimated to reduce the ability of coral reefs to keep pace with future SLR (Hughes et al., 2017 <sup>[[#fn:r1304|1304]]</sup> ; Yates et al., 2017 <sup>[[#fn:r1305|1305]]</sup> ) and thereby reduce the capacity of reefs to provide sediments and protection to coastal areas. For example, the combination of reef erosion due to acidification and human-induced mechanical destruction is altering seafloor topography, increasing risks from SLR in carbonate sediment dominated regions (Yates et al., 2017 <sup>[[#fn:r1306|1306]]</sup> ). Both ocean acidification (Albright et al., 2018 <sup>[[#fn:r1307|1307]]</sup> ; Eyre et al., 2018 <sup>[[#fn:r1308|1308]]</sup> ) and ocean warming (Perry and Morgan, 2017 <sup>[[#fn:r1309|1309]]</sup> ) have been considered to slow future growth rates and reef accretion (Section 5.3.4). Recent literature also shows that alterations of coral reef 3D structure from changes in growth, breakage, disease or acidification can profoundly affect their ability to buffer waves impacts (through wave breaking and wave energy damping), and therefore keep-up with SLR (Yates et al., 2017 <sup>[[#fn:r1310|1310]]</sup> ; Harris et al., 2018 <sup>[[#fn:r1311|1311]]</sup> ). Such prospects contribute to raise concerns about the future ability of atoll islands to adjust naturally to SLR and persist (Section 4.3.3.3, Cross-Chapter Box 9). Another concern is that locally, even minimal SLR can increase turbidity on fringing reefs, reducing light and, therefore, photosynthesis and calcification. SLR-induced turbidity can be caused by increased coastal erosion and the transfer of sediment to nearby reefs and enhanced sediment resuspension (Field et al., 2011 <sup>[[#fn:r1312|1312]]</sup> ).

<div id="section-4-3-3-5ecosystems-and-ecosystem-services-block-6"></div>

<span id="seagrasses"></span>
===== 4.3.3.5.3 Seagrasses =====

<div id="section-4-3-3-5ecosystems-and-ecosystem-services-block-7"></div>

Due to their natural capacity to enhance accretion and in the absence of mechanical or chemical destruction by human activities, seagrasses are not expected to be severely affected by SLR, except indirectly through the increase of the impacts of extreme weather events and waves on coastal morphology (i.e., erosion) as well as through changes in light levels and through effects on adjacent ecosystems (Saunders et al., 2013 <sup>[[#fn:r1313|1313]]</sup> ). Extreme ﬂooding events have also been shown to cause large-scale losses of seagrass habitats (Bandeira and Gell, 2003 <sup>[[#fn:r1314|1314]]</sup> ), for example seagrasses in Queensland, Australia, were lost in a disastrous ﬂooding event (Campbell and McKenzie, 2004 <sup>[[#fn:r1315|1315]]</sup> ). Changes in ocean currents can have either positive or negative effects on seagrasses, creating new space for seagrasses to grow or eroding seagrass beds (Bjork et al., 2008 <sup>[[#fn:r1316|1316]]</sup> ). But overall, seagrass will primarily be negatively affected by the direct effects of increased sea temperature on growth rates and the occurrence of disease (Marba and Duarte, 2010 <sup>[[#fn:r1317|1317]]</sup> ; Burge et al., 2013 <sup>[[#fn:r1318|1318]]</sup> ; Koch et al., 2013 <sup>[[#fn:r1319|1319]]</sup> ; Thompson et al., 2015 <sup>[[#fn:r1320|1320]]</sup> ; Chefaoui et al., 2018 <sup>[[#fn:r1321|1321]]</sup> ; Gattuso et al., 2018 <sup>[[#fn:r1322|1322]]</sup> ; Section 5.3.2) as well as by heavy rains that may dilute the seawater to a lower salinity. Such impacts will be exacerbated by major causes of seagrass decline including coastal eutrophication, siltation and coastal development (Waycott et al., 2009 <sup>[[#fn:r1323|1323]]</sup> ). Noteworthy is that some positive impacts are expected, as ocean acidification is expected to benefit photosynthesis and growth rates of seagrass (Repolho et al., 2017 <sup>[[#fn:r1324|1324]]</sup> ).

<div id="section-4-3-3-5ecosystems-and-ecosystem-services-block-8"></div>

<span id="coastal-protection-by-coastal-and-marine-ecosystems"></span>
===== 4.3.3.5.4 Coastal protection by coastal and marine ecosystems =====

<div id="section-4-3-3-5ecosystems-and-ecosystem-services-block-9"></div>

Major ‘protection’ benefits derived from the above-mentioned coastal ecosystems include wave attenuation and shoreline stabilisation, for example, by coral reefs (Elliff and Silva, 2017 <sup>[[#fn:r1325|1325]]</sup> ; Siegle and Costa, 2017 <sup>[[#fn:r1326|1326]]</sup> ), mangroves (Zhang et al., 2012 <sup>[[#fn:r1327|1327]]</sup> ; Barbier, 2016 <sup>[[#fn:r1328|1328]]</sup> ; Menéndez et al., 2018 <sup>[[#fn:r1329|1329]]</sup> ) or salt marshes (Möller et al., 2014 <sup>[[#fn:r1330|1330]]</sup> ; Hu et al., 2015 <sup>[[#fn:r1331|1331]]</sup> ). Recently, a global meta-analysis of 69 studies demonstrated that, on average, these ecosystems together reduced wave heights between 35–71% at the limited locations considered (Narayan et al., 2016 <sup>[[#fn:r1332|1332]]</sup> ), with coral reefs, salt marshes, mangroves and seagrass/kelp beds reducing wave heights by 54–81%, 62–79%, 25–37% and 25–45% respectively (see Narayan et al., 2016 for map of locations considered). Additional studies suggest greater wave attenuation in mangrove systems (Horstman et al., 2014 <sup>[[#fn:r1333|1333]]</sup> ), and highlight broader complexities in wave attenuation related to total tidal wetland extent, water depth, and species. Global analyses show that natural and artificial seagrasses can attenuate wave height and energy by as much as 40% and 50%, respectively (Fonseca and Cahalan, 1992 <sup>[[#fn:r1334|1334]]</sup> ; John et al., 2015 <sup>[[#fn:r1335|1335]]</sup> ), while coral reefs have been observed to reduce total wave energy by 94–98% (n = 13; Ferrario et al., 2014 <sup>[[#fn:r1336|1336]]</sup> ) and wave driven flooding volume by 72% (Beetham et al., 2017 <sup>[[#fn:r1337|1337]]</sup> ). In addition, storm surge attenuation based on a recent literature review by Stark et al. (2015) <sup>[[#fn:r1338|1338]]</sup> range from -2–25 cm km <sup>–1</sup> length of marsh, where the negative value denotes actual amplification. Other ecosystems provide coastal protection, including macroalgae, oyster and mussel beds, and also beaches, dunes and barrier islands, but there is less understanding of the level of protection conferred by these other organisms and habitats (Spalding et al., 2014 <sup>[[#fn:r1339|1339]]</sup> ).

While there is little literature on the extent to which SLR specifically will affect coastal protection by coastal and marine ecosystems, it is estimated that SLR may reduce this ecosystem service ( ''limited evidence, high agreement'' ) through the above-described impacts on the ecosystems themselves, and in combination with the impacts of other climate-related changes to the ocean (e.g., ocean warming and acidification; Sections 5.3.1 to 5.3.6, 5.4.1). Wave attenuation by coral reefs, for example, is estimated to be negatively affected in the near future by changes in coral reefs’ structural complexity more than by SLR (Harris et al., 2018 <sup>[[#fn:r1340|1340]]</sup> ); changes in mean and ESL events will rather add a layer of stress. Beck et al. (2018) estimate that under RCP8.5 by 2100, a 1 m loss in coral reefs’ height will increase the global area flooded under a 100-year storm event by 116% compared to today, against +66% with no reef loss.

<div id="section-4-3-3-6human-activities"></div>

<span id="human-activities"></span>
==== 4.3.3.6 Human Activities ====

<div id="section-4-3-3-6human-activities-block-1"></div>

<span id="coastal-agriculture"></span>
===== 4.3.3.6.1 Coastal agriculture =====

SLR will affect agriculture mainly through land submergence, soil and fresh groundwater resources salinisation, and land loss due to permanent coastal erosion, with consequences on production, livelihood diversification and food security, especially in heavily coastal agriculture-dependent countries such as Bangladesh (Khanom, 2016 <sup>[[#fn:r13|13]]</sup> 41). Recent literature confirms that salinisation is already a major problem for traditional agriculture in deltas (Wong et al., 2014 <sup>[[#fn:r1342|1342]]</sup> ; Khai et al., 2018 <sup>[[#fn:r1343|1343]]</sup> ) and low-lying island nations where some edible cultivated plants such as taro patches are threatened (Nunn et al., 2017b <sup>[[#fn:r1344|1344]]</sup> ). Taking the case of rice cultivation, recent works emphasise the prevailing role of combined surface elevation and soil salinity, such as in the Mekong delta (Vietnam; Smajgl et al., 2015 <sup>[[#fn:r1345|1345]]</sup> ) and in the Ebro delta (Spain; Genua-Olmedo et al., 2016 <sup>[[#fn:r1346|1346]]</sup> ), estimating for the latter a decrease in the rice production index from 61.2% in 2010 to 33.8% by 2100 in a 1.8 m SLR scenario. For seven wetland species occurring in coastal freshwater marshes in central Veracruz on the Gulf of Mexico, an increase in salinity was shown to affect the germination process under wetland salt intrusion (Sánchez-García et al., 2017 <sup>[[#fn:r1347|1347]]</sup> ). In coastal Bangladesh, oilseed, sugarcane and jute cultivation was reported to be already discontinued due to challenges to cope with current salinity levels (Khanom, 2016 <sup>[[#fn:r1348|1348]]</sup> ), and salinity is projected to have an unambiguously negative influence on all dry-season crops over the next 15–45 years (especially in the southwest; Clarke et al., 2018 <sup>[[#fn:r1349|1349]]</sup> ; Kabir et al., 2018 <sup>[[#fn:r1350|1350]]</sup> ). Salinity intrusion and salinisation can trigger land use changes towards brackish or saline aquaculture such as shrimp or rice-shrimp systems with impacts on environment, livelihoods and income stability (Renaud et al., 2015 <sup>[[#fn:r1351|1351]]</sup> ). However, increasing salinity is only one of the land use change drivers along with, for example, policy changes and market prices at the household level (Renaud et al., 2015 <sup>[[#fn:r1352|1352]]</sup> ).

<div id="section-4-3-3-6human-activities-block-2"></div>

<span id="coastal-tourism-and-recreation"></span>
===== 4.3.3.6.2 Coastal tourism and recreation =====

SLR may significantly affect tourism and recreation through impacts on landscapes (e.g., beaches), cultural features (e.g., Marzeion and Levermann, 2014; Fang et al., 2016 <sup>[[#fn:r1353|1353]]</sup> ), and critical transportation infrastructures such as harbours and airports (Monioudi et al., 2018 <sup>[[#fn:r1354|1354]]</sup> ). Coastal areas’ future tourism and recreation attractiveness will however also depend on changes in air temperature, seasonality and sea surface temperature (including induced effects such as invasive species, e.g., jellyfishes, and disease spreading; Burge et al., 2014 <sup>[[#fn:r1355|1355]]</sup> ; Weatherdon et al., 2016 <sup>[[#fn:r1356|1356]]</sup> ; Hoegh-Guldberg et al., 2018 <sup>[[#fn:r1357|1357]]</sup> ; Section 5.4.2). Future changes in climatic conditions in tourists’ areas of origin will also play a role in reshaping tourism flows (Bujosa and Rosselló, 2013 <sup>[[#fn:r1358|1358]]</sup> ; Amelung and Nicholls, 2014 <sup>[[#fn:r1359|1359]]</sup> ), in addition to mitigation policies on air transportation, non-climatic features (e.g., accommodation and travel prices) and tourists’ and tourism developers’ perceptions of climate-related changes (Shakeela and Becken, 2015 <sup>[[#fn:r1360|1360]]</sup> ). Since AR5, forecasting the consequences of climate change effects on global-to-local tourism flows has remained challenging (Rosselló-Nadal, 2014 <sup>[[#fn:r1361|1361]]</sup> ; Wong et al., 2014 <sup>[[#fn:r1362|1362]]</sup> ; Hoegh-Guldberg et al., 2018 <sup>[[#fn:r1363|1363]]</sup> ). There are also concerns about the effect of SLR on tourism facilities, for example hotels in Ghana (Sagoe-Addy and Addo, 2013 <sup>[[#fn:r1364|1364]]</sup> ), in a context where tourism infrastructure often contributes to the degradation of natural buffering environments through, for example, coastal squeeze (e.g., Section 4.3.2.4) and human-driven coastal erosion. Again, forecasting is constrained by the lack of scientific studies on tourism stakeholders’ long-term strategies and adaptive capacity (Hoogendoorn and Fitchett, 2018 <sup>[[#fn:r1365|1365]]</sup> ).

<div id="section-4-3-3-6human-activities-block-3"></div>

<span id="coastal-fisheries-and-aquaculture"></span>
===== 4.3.3.6.3 Coastal fisheries and aquaculture =====

Recent studies support the AR5 conclusion that ocean warming and acidification are considered more influential drivers of change in fisheries and aquaculture than SLR (Larsen et al., 2014; Nurse et al., 2014 <sup>[[#fn:r1366|1366]]</sup> ; Wong et al., 2014 <sup>[[#fn:r1367|1367]]</sup> ). The negative effects of SLR on fisheries and aquaculture are indirect, through adverse impacts on habitats (e.g., coral reef degradation, reduced water quality in deltas and estuarine environments, soil salinisation, etc.), as well as on facilities (e.g., damage to small and large harbours). This makes future projections on SLR implications for coastal and marine fisheries and aquaculture an understudied field of research. Conclusions only state that future impacts will be highly context-specific due to local manifestations of SLR and local fishery-dependent communities’ ability to adapt to alterations in fish and aquaculture conditions and productivity (Hollowed et al., 2013 <sup>[[#fn:r1368|1368]]</sup> ; Weatherdon et al., 2016 <sup>[[#fn:r1369|1369]]</sup> ). Salinity intrusion also contributes to conversion of land or freshwater ponds to brackish or saline aquaculture in many low-lying coastal areas of Southeast Asia such as in the Mekong Delta in Vietnam (Renaud et al., 2015 <sup>[[#fn:r1370|1370]]</sup> ).

<div id="section-4-3-3-6human-activities-block-4"></div>

<span id="social-values"></span>
===== 4.3.3.6.4 Social values =====

Social values refer to what people consider of critical importance about the places in which they live, and range from material to immaterial things (assets, beliefs, etc.; Hurlimann et al., 2014 <sup>[[#fn:r1371|1371]]</sup> ; Rouse et al., 2017 <sup>[[#fn:r1372|1372]]</sup> ). Consideration of social values offers an opportunity to address a wider perspective on impacts on human systems, for example, complementary to quantitative assessments of health impacts (e.g., loss of source of calories and food insecurity; Keim, 2010 <sup>[[#fn:r1374|1374]]</sup> ). This also encompasses immaterial dimensions, such as threats to cultural heritage (Marzeion and Levermann, 2014 <sup>[[#fn:r1374|1374]]</sup> ; Fatorić and Seekamp, 2017a <sup>[[#fn:r1375|1375]]</sup> ), socialising activities (Karlsson et al., 2015 <sup>[[#fn:r1376|1376]]</sup> ), integration of marginalised groups (Maldonado, 2015 <sup>[[#fn:r1377|1377]]</sup> ) and cultural ecosystem services (Fish et al., 2016), and provides an opportunity to better reflect context-specificities in valuing the physical/ecological/human/cultural impacts’ importance for and distribution within a given society (Fatorić and Seekamp, 2017b <sup>[[#fn:r1379|1379]]</sup> ). This field of research (no detailed mention found in AR5) is just emerging due to the transdisciplinary and qualitative nature of the topic. Graham et al. (2013) <sup>[[#fn:r1380|1380]]</sup> advance a 5-category framing of social values specifically at risk from SLR: health (i.e., the social determinants of survival such as environmental and housing quality and healthy lifestyles), feeling of safety (e.g., financial and job security), belongingness (i.e., attachment to places and people), self-esteem (e.g., social status or pride that can be affected by coastal retreat), and self-actualisation (i.e., people’s efforts to define their own identity). Another emerging issue relates to social values at risk due to land submergence in low-lying islands (Yamamoto and Esteban, 2014 <sup>[[#fn:r1381|1381]]</sup> ) and parts of countries and individual properties (Marino, 2012 <sup>[[#fn:r1382|1382]]</sup> ; Maldonado et al., 2013 <sup>[[#fn:r1383|1383]]</sup> ; Aerts, 2017 <sup>[[#fn:r1384|1384]]</sup> ; Allgood and McNamara, 2017 <sup>[[#fn:r1385|1385]]</sup> ). Recent studies also highlight the potential additional risks to social values in areas where displaced people relocate (Davis et al., 2018 <sup>[[#fn:r1386|1386]]</sup> ).

<span id="conclusion-on-coastal-risk-reasons-for-concern-and-future-risks"></span>