Coastal critical infrastructures

Climate-related hazards are projected to increase marine heatwaves, rising sea levels and extreme precipitation events that have high impacts in coastal zones (Collins et al., Reference Collins, Sutherland, Bouwer, Cheong, Frolicher, Jacot Des Combes, Koll Roxy, Losada, McInnes, Ratter, Rivera-Arriaga, Susanto, Swingedouw, Tibig, Pörtner, Roberts, Masson-Delmotte and Weyer2019). Coastal urban centres are agglomerations of dense settlements, high-value assets and real estate, as well as critical infrastructure that are highly exposed to coastal erosion, storm surges and pluvial flooding (Glavovic et al., Reference Glavovic, Dawson, Chow, Garschagen, Haasnoot, Singh, Thomas, Pörtner, Roberts, Tignor and Rama2022). Human security dimensions here deal, for example, with climate-related hazards and extreme events on coastal energy, transport and water infrastructures, as well as the associated effects on social infrastructures and systems, which are highly interconnected (Pal et al., Reference Pal, Kumar and Mukhopadhyay2023). While current research still focuses on physical infrastructure (Huddleston et al., Reference Huddleston, Smith, White and Elrick-Barr2022), there is an increasing understanding of the importance of analysing human security impacts through cascading events, including direct and indirect effects on social systems (Barquet et al., Reference Barquet, Englund, Inga, André and Segnestam2023) and compound risks that result from the combination of multiple climate hazards and interplay with anthropogenic drivers of coastal exposure and vulnerability (Cutter, Reference Cutter2018; Collins et al., Reference Collins, Sutherland, Bouwer, Cheong, Frolicher, Jacot Des Combes, Koll Roxy, Losada, McInnes, Ratter, Rivera-Arriaga, Susanto, Swingedouw, Tibig, Pörtner, Roberts, Masson-Delmotte and Weyer2019).

Water, food and fisheries

The nexus of water, food and human security is sensitive to environmental and climate change, including saltwater penetration by sea level rise, storms, floods and subsidence by groundwater loss. Risks to coastal ecosystem services affect freshwater provision, storage and regulation; groundwater flows; aquifer recharge and wetland flooding (Hérivaux et al., Reference Hérivaux, Rey-Valette, Rulleau, Agenais, Grisel, Kuhfuss, Maton and Vinchon2018).

Coastal waters can be overloaded with terrestrial nutrients and chemical, biological and physical pollutants, toxins and pathogens (Cooley et al., Reference Cooley, Schoeman, Bopp, Boyd, Donner, Ito, Kiessling, Martinetto, Ojea, Racault, Rost, Skern-Mauritze, Ghebrehiwet, Pörtner, Roberts, Tignor and Rama2022). While the salinities of many estuaries, deltas, aquifers and soils are increasing, decreasing water quality is endangering human health, agricultural yields (Rakib et al., Reference Rakib, Sasaki, Matsuda, Quraishi, Mahmud, Bodrud-Doza, Ullah, Fatema, Newaz and Bhuiyan2020; Mastrocicco and Colombani, Reference Mastrocicco and Colombani2021) and drinking water availability (Sithara et al., Reference Sithara, Pramada and Thampi2020; Wang and Hong, Reference Wang and Hong2021) which depend heavily on regional variations in environment and human behaviour (Paldor and Michael, Reference Paldor and Michael2021). Water security is also threatened by various direct anthropogenic interventions that degrade coastal ecosystems, such as cutting mangroves, overexploitation of groundwater and pollution, resulting in poverty, tensions and instability (Babuna et al., Reference Babuna, Yang, Tulcan, Dehui, Takase, Guba, Han, Awudi and Li2023). With climate change, coastal water security is becoming intractable, requiring empowerment to avoid vicious circles (Powell et al., Reference Powell, Kløcker Larsen, De Bruin, Powell and Elrick-Barr2017).

Climate and environmental stress reduce coastal food security through decreasing crops, livestock and fishery, soil fertility and agricultural productivity, cultivable land and safe water, affecting livelihoods, especially for marginalised smallholder farmers (Shams and Shohel, Reference Shams and Shohel2016) with low investments in resilient infrastructure (Ismail et al., Reference Ismail, Singh, Sarangi, Srivastava, Bhowmick, Lama, Burman, Mandal, Sarangi and Sen2022). Regional studies show the effect of land fragmentation on farm efficiency and diversification in household food security in Vietnam (Tran and Van Vu, Reference Tran and Van Vu2021) and climate challenges on Arctic food security, weakening food sovereignty and destabilising indigenous practices (Zimmermann et al., Reference Zimmermann, Dermody, Theunissen, Wassen, Divine, Padula, von Wehrden and Dorresteijn2023). Coastal households of Bangladesh had a significantly lower Food Consumption Score than other areas (Rahman et al., Reference Rahman, Zulfiqar, Ullah, Himanshu and Datta2023). Perceptions of small-scale fishers in Bangladesh show that wellbeing is more associated with fish yield than climatic stress (Alam and Mallick, Reference Alam and Mallick2022).

Linking ocean and land food supply chains across coasts, marine fisheries and aquaculture provide a significant fraction of human animal protein (Costello et al., Reference Costello, Cao, Gelcich, Cisneros-Mata, Free, Froehlich, Golden, Ishimura, Maier, Macadam-Somer, Mangin, Melnychuk, Miyahara, de Moor, Naylor, Nøstbakken, Ojea, O’Reilly, Parma, Plantinga, Thilsted and Lubchenco2020), dietary micronutrients (Vianna et al., Reference Vianna, Zeller and Pauly2020), livelihoods and income (Harper et al., Reference Harper, Adshade, Lam, Pauly and Sumaila2020), in particular in Small Island Developing States and Indigenous Peoples (Cisneros-Montemayor et al., Reference Cisneros-Montemayor, Pauly, Weatherdon and Ota2016). Temperature is a major driver of fishery changes, with other factors like acidification, deoxygenation and sea ice loss, placing many fisheries at risk of collapse, affecting fishery biomass, food web, catch and value (Olsen et al., Reference Olsen, Kaplan, Ainsworth, Fay, Gaichas, Gamble, Girardin, Eide, Ihde, Morzaria-Luna, Johnson, Savina-Rolland, Townsend, Weijerman, Fulton and Link2018). Declining fish stocks are expected to have detrimental effects on marine life, ecosystems and services, harming dependent human communities, including Arctic Indigenous Peoples (Steiner et al., Reference Steiner, Cheung, Cisneros-Montemayor, Drost, Hayashida, Hoover, Lam, Sou, Sumaila, Suprenand, Tai and VanderZwaag2019). Global warming drives ocean and coastal fauna towards higher latitudes, challenging fishers to change habits and management (Smith et al., Reference Smith, Dowling and Brown2019).

Human wellbeing and health

Health security is closely linked to climate-related disasters and impacts on water, food and fishing. On the one hand, physical health concerns in coastal regions refer to malnutrition due to climate-related impacts, such as ocean warming and acidification, on fisheries, as well as direct and indirect health impacts from ocean warming, sea level rise and storm surges, including injuries and increasing exposure to waterborne diseases (Weatherdon et al., Reference Weatherdon, Magnan, Rogers, Sumaila and Cheung2016; Banwell et al., Reference Banwell, Rutherford, Mackey, Street and Chu2018; Bindoff et al., Reference Bindoff, Cheung, Kairo, Aristegui, Guinder, Hallberg, Hilmi, Jiao, Karim, Levin, O’Donoghue, Purca Cuicapusa, Rinkevich, Suga, Tagliabue, Williamson, Pörtner, Roberts, Masson-Delmotte and Weyer2019; Pugatch, Reference Pugatch2019). On the other hand, there is increasing evidence and research attention to mental health impacts on coastal communities due to increased stress caused by climate-related hazards and pressure to adapt, as well as loss of local livelihoods and cultural heritage due to the impacts of climate change (i.e., ecological grief, solastalgia) (Cunsolo and Ellis, Reference Cunsolo and Ellis2018; Kelman et al., Reference Kelman, Ayeb-Karlsson, Rose-Clarke, Prost, Ronneberg, Wheeler and Watts2021; Phillips and Murphy, Reference Phillips and Murphy2021). Such impacts are especially critical and documented in indigenous coastal communities with strong ties to their local environment (Donatuto et al., Reference Donatuto, Grossman, Konovsky, Grossman and Campbell2014; Ford et al., Reference Ford, Willox, Chatwood, Furgal, Harper, Mauro and Pearce2014).

Human mobility and displacement

Several types of human mobility in coastal zones are related to climate change impacts, especially sea level rise, such as migration, displacement, relocation, retreat or resettlement (Oppenheimer et al., Reference Oppenheimer, Glavovic, Hinkel, Van de Wal, Magnan, Abd-Elgawad, Cai, Cifuentes-Jara, Ghosh, DeConto, Hay, Isla, Marzeion, Meyssignac, Sebesvari, Pörtner, Roberts, Masson-Delmotte and Rama2019). Migration towards coasts can be a driver of vulnerability and exposure, especially in urban areas (Reimann et al., Reference Reimann, Vafeidis and Honsel2023b, Reference Reimann, Jones, Bieker, Wolff, Aerts and Vafeidis2023a), where it increases population numbers and densities and often also includes people with higher vulnerability, such as migrant workers without social security (Hari et al., Reference Hari, Dharmasthala, Koppa, Karmakar and Kumar2021). Migration away from the coast due to climate change impacts has been discussed prominently and controversially in the context of displacement and climate refugees (Boas et al., Reference Boas, Farbotko, Adams, Sterly, Bush, van der Geest, Wiegel, Ashraf, Baldwin, Bettini, Blondin, de Bruijn, Durand-Delacre, Fröhlich, Gioli, Guaita, Hut, Jarawura, Lamers, Lietaer, Nash, Piguet, Rothe, Sakdapolrak, Smith, Tripathy Furlong, Turhan, Warner, Zickgraf, Black and Hulme2019; Lincke and Hinkel, Reference Lincke and Hinkel2021; Farbotko and Campbell, Reference Farbotko and Campbell2022). Planned relocation in the form of resettlement programmes or managed retreat is a type of adaptation, especially to sea level rise (Ferris and Weerasinghe, Reference Ferris and Weerasinghe2020). However, there is uncertainty regarding the precise number of people exposed to increasing sea level as well as its implications for potential climate-related migration. On the one hand, there are several model-based studies with a wide range of assumed population numbers exposed to inundation related to different sea level rise and population projections, but without considering potential adaptation (Hauer et al., Reference Hauer, Fussell, Mueller, Burkett, Call, Abel, McLeman and Wrathall2019; McMichael et al., Reference McMichael, Dasgupta, Ayeb-Karlsson and Kelman2020). On the other hand, studies including assumptions on coastal protection and autonomous adaptation as well as evidence from local case studies demonstrate that exposed populations may have rather higher threshold for out-migration (Esteban et al., Reference Esteban, Takagi, Jamero, Chadwick, Avelino, Mikami, Fatma, Yamamoto, Thao, Onuki, Woodbury, Valenzuela, Crichton and Shibayama2020; Bachner et al., Reference Bachner, Lincke and Hinkel2022).

Besides the potential to reduce risks, all these forms of human mobility can have significant human security impacts since they may involve losses of livelihoods, homes, place attachment, identities, social networks and the potential for conflict between individuals and communities (Black et al., Reference Black, Arnell, Adger, Thomas and Geddes2013). Hence, they are discussed from an environmental justice perspective (Siders, Reference Siders2019; Ajibade et al., Reference Ajibade, Sullivan and Haeffner2020) but also as necessary responses and opportunities in the face of projected climate change impacts in coastal areas (Haasnoot et al., Reference Haasnoot, Lawrence and Magnan2021; Bower et al., Reference Bower, Badamikar, Wong-Parodi and Field2023). At the same time, immobility is increasingly discussed, that is, people or communities who cannot or do not want to move despite climate change impacts (Farbotko et al., Reference Farbotko, Dun, Thornton, McNamara and McMichael2020; McMichael et al., Reference McMichael, Schwerdtle and Ayeb-Karlsson2023).

Societal stability and conflict

There are many conflicts in coastal regions (Dahlet et al., Reference Dahlet, Selim and Van Putten2023), from war and civil war to tensions over the impacts and consequences of weather extremes or disputes over coastal protection and who pays. Populated coastal regions are particularly sensitive to conflict and multiple environmental hazards (Stepanova and Bruckmeier, Reference Stepanova and Bruckmeier2013). Climate-conflict links may affect human security, where climate change is a driver of conflict risk, while conflict can drive climate risk (Mach et al., Reference Mach, Adger, Buhaug, Burke, Fearon, Field, Hendrix, Kraan, Maystadt, O’Loughlin, Roessler, Scheffran, Schultz and von Uexkull2020; Scheffran, Reference Scheffran and Kurtz2022). Coastal storms, floods and sea level rise can undermine the conditions for stability and peace in vulnerable and fragile populations. At the same time, conflict can weaken protective and adaptive capacities against climate impacts. Combined effects of conflict and climate change can destroy dams and dikes and undermine aid and cooperative arrangements for climate protection. Multiple compound risks can trigger a vicious circle of mutually enforcing crises (Buhaug and Von Uexkull, Reference Buhaug and Von Uexkull2021).

Inland and coastal climate-conflict risks can be connected, for example, when people move to the coast where they participate in violent conflict, end up in urban slums or are exposed to coastal risks. Failure to secure the lives and assets of coastal populations can lead to social disruption, tension, instability and displacement. Coastal infrastructures are vulnerable to both climate and conflict impacts, including energy systems and military facilities (Howland, Reference Howland2022). Other forms of coastal conflict involve interest groups, notably those threatening or conserving marine ecology and biodiversity. In the world’s “oceans of conflict” (Nyman, Reference Nyman2013), climate change is one of multiple stressors in fishery conflict, particularly in the North-East Atlantic, East China Sea, West African coast and the Arctic (Spijkers et al., Reference Spijkers, Merrie, Wabnitz, Osborne, Mobjörk, Bodin, Selig, le Billon, Hendrix, Singh, Keys and Morrison2021).

Islands

The literature on human security concerns on small islands often focuses on questions of habitability of low-lying islands due to sea level rise (Farbotko, Reference Farbotko2010; Kelman, Reference Kelman2018; Spencer et al., Reference Spencer, Magnan, Donner, Garschagen, Ford, Duvat and Wabnitz2024). While there is increasing evidence that large shares of island populations will be faced with inundations by 2050 (Mycoo et al., Reference Mycoo, Wairiu, Campbell, Duvat, Golbuu, Maharaj, Nalau, Nunn, Pinnegar, Warrick, Pörtner, Roberts, Tignor and Rama2022), there are also studies demonstrating how reef islands can adjust to sea level change, offering alternative opportunities of adaptation beyond relocation (Masselink et al., Reference Masselink, Beetham and Kench2020; Kench et al., Reference Kench, Liang, Ford, Owen, Aslam, Ryan, Turner, Beetham, Dickson, Stephenson, Vila-Concejo and McLean2023). Moreover, the question of what such evidence, together with other observed climate impacts, means for habitability remains debated due to multiple and diverging perspectives on when experiences of inundation become unbearable (Moftakhari et al., Reference Moftakhari, AghaKouchak, Sanders, Allaire and Matthew2018; Spencer et al., Reference Spencer, Magnan, Donner, Garschagen, Ford, Duvat and Wabnitz2024) or an island becomes effectively uninhabitable (Farbotko and Campbell, Reference Farbotko and Campbell2022). Besides potential inundation due to sea level rise, also the other dimensions of human security are highly relevant and with increasing evidence in the scientific literature, especially regarding Small Island Developing States (SIDS), but also other island geographies (Petzold and Magnan, Reference Petzold and Magnan2019; Duvat et al., Reference Duvat, Magnan, Perry, Spencer, Bell, Wabnitz, Webb, White, McInnes, Gattuso, Graham, Nunn and le Cozannet2021; Mycoo et al., Reference Mycoo, Wairiu, Campbell, Duvat, Golbuu, Maharaj, Nalau, Nunn, Pinnegar, Warrick, Pörtner, Roberts, Tignor and Rama2022; Ortiz et al., Reference Ortiz, Jamero, Crespin, Smith Ramirez, Matias, Reyes, Pauchard and la Viña2023b).

Especially in low-lying atoll or barrier islands, basically all housing and infrastructure are located on or close to the coast. In these cases, hurricanes or tropical cyclones can devastate whole islands and their infrastructure. The island of Barbuda, for example, was devastated and had to be evacuated entirely after Hurricane Irma in 2017 (Burn et al., Reference Burn, Boger, Holmes, Bain, Perdikaris and Boger2022). Apart from extreme events and impacts on critical infrastructure, there is a strong focus in the literature on climate-related impacts on the tourism sector since they make up a significant share of many economies of SIDS and other island types (Posen et al., Reference Posen, Beraud, Harper Jones, Tyllianakis, Joseph-Witzig and St. Louis2023). Depending on the island context and the specific kind of tourism, slow-onset hazards, such as sea level rise, ocean warming, or shifting seasons, as well as fast onset events, such as flooding, can affect individual tourism activities, sites and periods as well as whole tourism economics (Wolf et al., Reference Wolf, Filho, Singh, Scherle, Reiser, Telesford, Miljković, Havea, Li, Surroop and Kovaleva2021; Carrillo et al., Reference Carrillo, González, Pérez, Expósito and Díaz2022).

Food and water insecurity on small islands result from cyclones, droughts, saline intrusion and ocean warming that directly impact agriculture and fisheries. Food security is threatened, especially by the observed decline in fisheries, which affects the main diet in many small island communities (Mycoo et al., Reference Mycoo, Wairiu, Campbell, Duvat, Golbuu, Maharaj, Nalau, Nunn, Pinnegar, Warrick, Pörtner, Roberts, Tignor and Rama2022). Hence, climate change impacts island communities’ ability to produce, import or purchase food (Barnett, Reference Barnett, Connell and Lowitt2020). Accordingly, there is increasing attention to the social dimensions of food security in small islands, with poor population groups particularly affected (Lincoln Lenderking et al., Reference Lincoln Lenderking, Robinson and Carlson2021).

Climate impact on the wellbeing of island communities is closely linked to food insecurity due to potential undernutrition. Other prominent health impacts result from the increasing and shifting range of vector-borne diseases (Thomas et al., Reference Thomas, Baptiste, Martyr-Koller, Pringle and Rhiney2020). Relatively little but increasing attention in the literature is being paid to mental health impacts on islands, for example, anxiety and stress due to changing weather patterns and depression due to the inability to adapt livelihoods to climate-induced environmental changes and degradation (Kelman et al., Reference Kelman, Ayeb-Karlsson, Rose-Clarke, Prost, Ronneberg, Wheeler and Watts2021). Related concepts that are gaining prominence and with relevance to islands are those around non-economic loss and damage (Thomas and Benjamin, Reference Thomas and Benjamin2020; McNamara et al., Reference McNamara, Westoby, Clissold and Chandra2021), ecological grief (Cunsolo and Ellis, Reference Cunsolo and Ellis2018) and solastalgia (McNamara and Westoby, Reference McNamara and Westoby2011) due to climate change-induced degradation and loss of habitats and landscapes. Going beyond the traditional concept of health, there are attempts to widen our understanding of wellbeing, which is especially important for climate-affected indigenous communities such as those on Pacific islands, who consider, for example, people-place connections and traditional knowledge systems central parts of wellbeing (Sterling et al., Reference Sterling, Pascua, Sigouin, Gazit, Mandle, Betley, Aini, Albert, Caillon, Caselle, Cheng, Claudet, Dacks, Darling, Filardi, Jupiter, Mawyer, Mejia, Morishige, Nainoca, Parks, Tanguay, Ticktin, Vave, Wase, Wongbusarakum and McCarter2020).

Human mobility in the context of climate change has different dimensions and human security implications on small islands. In many island and archipelagic communities, such as in the Pacific, migration is part of people’s livelihood strategy and, therefore, an important aspect contributing to the security of these populations (Connell, Reference Connell2016). On the other hand, forced displacement or migration due to climate risk is considered a last resort, if at all (Thomas et al., Reference Thomas, Baptiste, Martyr-Koller, Pringle and Rhiney2020; Piggott-McKellar and McMichael, Reference Piggott-McKellar and McMichael2021). Nonetheless, due to the potential loss of habitability of islands due to climate impacts, relocation of communities is increasingly discussed as necessary and important part of risk reduction in response to climate change (Magnan et al., Reference Magnan, Oppenheimer, Garschagen, Buchanan, Duvat, Forbes, Ford, Lambert, Petzold, Renaud, Sebesvari, van de Wal, Hinkel and Pörtner2022). Human security concerns around climate-induced migration, displacement or retreat on small islands relate to the resulting loss of place attachment, livelihoods, financial resources, community cohesion and social networks (Dannenberg et al., Reference Dannenberg, Frumkin, Hess and Ebi2019). Moreover, climate-induced migration and relocation can lead to conflicts between migrants and host communities and within migrant communities, for example, due to power struggles, ethnical conflicts and competition for land (Donner, Reference Donner2015). However, there is little evidence for such conflicts (Weir and Virani, Reference Weir and Virani2011; Kelman, Reference Kelman2015).

Coastal settlements and megacities

A great deal of literature on climate change impacts on coastal settlements deals with coastal megacities and impacts on critical urban infrastructure and livelihoods (Pelling and Blackburn, Reference Pelling and Blackburn2013). Many of the most vulnerable coastal cities lie in the tropics, including megacities such as Mumbai and Guangzhou and other major agglomerations such as Abidjan or Guayaquil (Hallegatte et al., Reference Hallegatte, Green, Nicholls and Corfee-Morlot2013). Impacts on critical infrastructure such as roads and harbours do not only directly affect cities and their populations but also trade networks and supply chains and are therefore felt far beyond the city context (Glavovic et al., Reference Glavovic, Dawson, Chow, Garschagen, Haasnoot, Singh, Thomas, Pörtner, Roberts, Tignor and Rama2022). Most affected by environmental pressures and hazards related to climate change in urban areas are low-income populations in the Global South (Adelekan et al., Reference Adelekan, Cartwright, Chow, Colenbrander, Dawson, Garschagen, Haasnoot, Hashizume, Klaus, Krishnaswamy, Fernanda Lemos, Ley, McPhearson, Pelling, Portner, Revi, Sara, Simpson, Singh, Solecki, Thomas and Trisos2022) and underprivileged ethnicities (Gran Castro and Ramos De Robles, Reference Gran Castro and Ramos De Robles2019) who suffer from social or ethnic exclusion, low-quality or non‑existent infrastructure, little tenure security and restricted access to resources and services.

The literature on food insecurity due to climate change focuses rather on rural or smaller coastal settlements than on megacities, with a higher degree of resource-dependent and subsistence populations, for example, in coastal Bangladesh, where increased salinity impacts the agricultural harvests and fisheries (Hanazaki et al., Reference Hanazaki, Berkes, Seixas and Peroni2013; Lam et al., Reference Lam, Winch, Nizame, Broaddus-Shea, Harun and Surkan2022). Nonetheless, especially the fishing sector is still an important economic element in many larger coastal cities, such as Jakarta, on which many livelihoods depend (Padawangi, Reference Padawangi and Holt2012). Water insecurity in coastal cities is caused by a growing demand of increasing urban populations and changing water availability due to climate change (Flörke et al., Reference Flörke, Schneider and McDonald2018). Desalination of sea water as a response to water scarcity in coastal cities may reduce water stress but can negatively impact coastal and marine ecosystems (Roberts et al., Reference Roberts, Johnston and Knott2010).

Health security in coastal cities is affected by extreme events, such as tropical cyclones, hurricanes and flooding. Flooding can result in the spread of waterborne diseases, to which especially populations in informal settlements are vulnerable, who lack adequate flood protection and suffer from insufficient sanitary infrastructure (Dawson et al., Reference Dawson, Khan, Gornitz, Lemos, Atkinson, Pullen, Osorio, Usher, Rosenzweig, Solecki, Romero-Lankao, Mehrotra, Dhakal and Ibrahim2018). In the coastal megacities of Mumbai, for example, a large share of the population lives in slums, which experience inundations regularly due to pluvial flooding (Romero-Lankao et al., Reference Romero-Lankao, Gnatz and Sperling2016). Other coastal cities that suffer from subsidence also experience coastal flooding, with marginalised communities most affected (Nurhidayah and McIlgorm, Reference Nurhidayah and McIlgorm2019; Cao et al., Reference Cao, Esteban, Valenzuela, Onuki, Takagi, Thao and Tsuchiya2021).

Sea level rise is expected to trigger displacement from coastal settlements, differing between geographic and socioeconomic contexts. Forced displacement is expected to be less relevant in larger coastal cities of the Global North (Magnan et al., Reference Magnan, Oppenheimer, Garschagen, Buchanan, Duvat, Forbes, Ford, Lambert, Petzold, Renaud, Sebesvari, van de Wal, Hinkel and Pörtner2022) where high investments are made to protect valuable assets, real estate and infrastructure. Smaller towns and rural areas already deal with managed retreat (Dannenberg et al., Reference Dannenberg, Frumkin, Hess and Ebi2019). Moreover, in several megacities of the Global South, especially the informal settlements face forced evictions due to their vulnerability to flooding, which can result in conflicts and unsustainable outcomes for the affected populations (Ahmed and Meenar, Reference Ahmed and Meenar2018; Ajibade, Reference Ajibade2019). While impacts on mental health are documented mainly in smaller coastal settlements and resource-dependent communities, the stress of worsening urban flood events for low-income communities and potential forced displacement has mental health implications, especially for the poor and marginalised ones (Neria and Shultz, Reference Neria and Shultz2012; Lane et al., Reference Lane, Charles-Guzman, Wheeler, Abid, Graber and Matte2013; Garrett et al., Reference Garrett, Clitherow, White, Wheeler and Fleming2019).

River deltas and estuaries

River delta regions benefit from the combination of abundant water, agriculturally fertile floodplains, ports, economic production and trade, contributing to human wealth and wellbeing. Many of the largest port cities are located in delta formations (Campanella, Reference Campanella2010), and more than 300 million people live in 40 deltas, including all the major megadeltas (Ericson et al., Reference Ericson, Vorosmarty, Dingman, Ward and Meybeck2006). A large number of people live in the river deltas of the Ganges-Brahmaputra, Pearl River and Nile. Populations face human security risks when river deltas and estuaries are vulnerable to the combined effects of climate change and intensive human use, both from the land and ocean sides, which interact in complex ways (Nicholls et al., Reference Nicholls, Adger, Hutton and Hanson2020). The ecological sensitivity in transition zones makes them predestined to become hot spots for climate change impacts. Physical variables (temperature, salinity, flow direction and velocity) and societal parameters (e.g., resource use, sediment input or removal, water quality impairment and sediment discharge) interact with secondary effects in delta regions of flooding, water shortages or droughts.

Rising sea levels in river deltas can lead to flooding, subsidence, saltwater intrusion, loss of coastal wetlands or declining quality of agricultural land. Since the beginning of the 21st century, 85% of the world’s largest river deltas have experienced severe flooding, at least temporarily submerging some 260,000 km² of land area (Syvitski et al., Reference Syvitski, Kettner, Overeem, Hutton, Hannon, Brakenridge, Day, Vörösmarty, Saito, Giosan and Nicholls2009). Considering the predicted changes in rainfall variability, extreme weather events and rising sea levels, highly vulnerable areas in coastal or deltaic regions will be increasingly challenged (Tessler et al., Reference Tessler, Vörösmarty, Grossberg, Gladkova, Aizenman, Syvitski and Foufoula-Georgiou2015) by large‑scale damages and loss of life (Brondizio et al., Reference Brondizio, Vogt, Mansur, Anthony, Costa and Hetrick2016). Climate-related hazards affect exposed infrastructures and resources and, in the long term, may lead to societal impacts on life and health, eventually resulting in migration, resettlement and displacement from delta regions. Cities in urban deltas of developing countries face compounding effects of high exposure and low adaptive capacities (Bangalore et al., Reference Bangalore, Smith and Veldkamp2019). In many delta regions, the most affected are the urban poor, for instance, the Black poor during Hurricane Katrina 2005 (Kates et al., Reference Kates, Colten, Laska and Leatherman2006) or informal settlers in the 2015 flood in the Jacuí River delta (Pereira Santos et al., Reference Pereira Santos, Rodriguez-Lopez, Chiarel and Scheffran2022).

These challenges affect all major river deltas, to different degrees depending on geographic location (Scheffran and Link, Reference Scheffran, Link, Lozan, Breckle, Grassl, Kuttler and Matzarakis2019). The most vulnerable urban deltas in 2050, measured as a share of gross domestic product (GDP) losses, would be Guangzhou, Mumbai, Kolkata, Guayaquil, Shenzen, Miami, Tianjin, New York, Ho Chi Minh City and New Orleans (Ovink, Reference Ovink2015). Without fundamental changes, about 2 billion people could be affected by 2050 and 4 billion by 2080. Key problem factors in selected river deltas are spatial pressure, flood vulnerability, drinking water shortages, ageing or inadequate infrastructure, coastal erosion and loss of environmental quality and biodiversity (Ovink, Reference Ovink2015).

While the Mediterranean Basin is largely rocky, river deltas face increased erosion patterns, decreased sediment discharge, intensification of floods, saltwater intrusion and loss of biodiversity, multiplied by climate change. Besides the Italian Po Delta, these issues concern the Spanish Ebro Delta, where human management has had a higher impact than climate change (Fatorić and Chelleri, Reference Fatorić and Chelleri2012). The heavy urban use of Nile water in the Cairo region also has a negative impact on water quality in the delta. Therefore, (mostly fossil) groundwater is regularly used to irrigate agricultural land. This results in saltwater inflows into groundwater or land subsidence when groundwater aquifers are drained (Mabrouk et al., Reference Mabrouk, Jonoski, H. P. Oude Essink and Uhlenbrook2018), increasing the relative effect of rising sea levels. The Nile Delta cannot be easily protected by hard coastal protection measures (Link et al., Reference Link, Kominek and Scheffran2013; Mabrouk et al., Reference Mabrouk, Jonoski, H. P. Oude Essink and Uhlenbrook2018).

The Pearl River Delta (PRD) is sensitive and variable due to the strong monsoon, dense river network and significant effects of erosion and sedimentation. The combination of rapid economic development, population growth and climate change makes the PRD vulnerable to flooding and other disasters (Yang et al., Reference Yang, Scheffran, Qin and You2015). Even small-scale sea level rise increases storm surge risk and post-storm reconstruction costs. Damage is high in low-lying urban areas with high levels of prosperity and vital infrastructure. In large cities such as Hong Kong, Shenzhen and Guangzhou, the population is particularly vulnerable to flood hazards.

In other parts of the world, delta vulnerability to climate change also combines with local factors, such as agricultural livelihoods in Bangladesh sensitive to salinity intrusion (Khanom, Reference Khanom2016), or civil conflict and violent skirmishes between herders and farmers in Kenya’s Tana River Delta (Kirchner, Reference Kirchner2013).

Coastal governance

Overall, there is increasing evidence of adaptation in coastal areas around the globe, especially in urban areas, which, however, is still far behind the adaptation potential and need, and lacking of long-term pathways approaches based on early warning and anticipative governance (Magnan et al., Reference Magnan, Bell, Duvat, Ford, Garschagen, Haasnoot, Lacambra, Losada, Mach, Noblet, Parthasaranthy, Sano, Vincent, Anisimov, Hanson, Malmström, Nicholls and Winter2023a). Political ecology approaches in coastal governance include issues of power and politics, knowledge and narratives, scale and history, justice and fairness (Zou et al., Reference Zou, Zhang, Lee and Tsai2023). Facing human security risks in coastal regions, effective and integrative governance is needed to shape coastal futures through institutions, norms, rules, laws and procedures that manage, implement and monitor policies at local to global scales. Governance can be adaptive to maintain a desired state under changing conditions, polycentric with multiple decision-making bodies and multi-level, including local to global scales (Jordan et al., Reference Jordan, Huitema, Van Asselt and Forster2018; Carlisle and Gruby, Reference Carlisle and Gruby2019). Multi-level governance, coordination and knowledge co-production across societal actors are required also for more transformational adaptation (Ratter and Leyshon, Reference Ratter, Leyshon and Storch2021; Rölfer et al., Reference Rölfer, Celliers and Abson2022; Niamir and Pachauri, Reference Niamir and Pachauri2023), although there is limited evidence of implemented governance concepts for transformational coastal adaptation (Bouwer et al., Reference Bouwer, Cheong, Jacot Des Combes, Frölicher, McInnes, Ratter and Rivera-Arriaga2022).

Climate and ocean governance can use the power of governments, nature and communities utilising different forms of governance capacity that need to be coordinated to resolve conflicts (Kullenberg, Reference Kullenberg2010). For example, in terms of coastal critical infrastructure, this implies building early warning systems and adaptive capacity across different levels of organisation, especially where it comes to the task of effectively implementing local adaptation actions (Huddleston et al., Reference Huddleston, Smith, White and Elrick-Barr2023). However, the current academic evidence base is strongly biased towards assessing risk, planning and monitoring rather than implementing coastal adaptation, and lacks an integration of existing coastal management and governance instruments with climate change adaptation frameworks (Cabana et al., Reference Cabana, Rölfer, Evadzi and Celliers2023). A synthesis to understand and manage cross-sectoral governance conflicts highlights conceptual differences and commonalities across disciplines to develop problem-solving frameworks of coastal and marine governance, including ecosystem-based management, adaptive co-management, integrated management, collaborative governance and marine spatial planning, and others (Bellanger et al., Reference Bellanger, Speir, Blanchard, Brooks, Butler, Crosson, Fonner, Gourguet, Holland, Kuikka, le Gallic, Lent, Libecap, Lipton, Nayak, Reid, Scemama, Stephenson, Thébaud and Young2020).

Coastal management and protection

Coastal protection against human security risks of climate change is a societal task that relies on government measures and resources to prevent coastline retreat and defend settlements and infrastructure at the shore and hinterland from storm- or sea level-related flooding and erosion. Engineering-based hard structures (such as breakwaters, dikes or seawalls) (Sorensen, Reference Sorensen2006) are complemented by soft measures embedded into social and ecological systems, involving the participation of stakeholders and social-science perspectives (Magnan et al., Reference Magnan, Oppenheimer, Garschagen, Buchanan, Duvat, Forbes, Ford, Lambert, Petzold, Renaud, Sebesvari, van de Wal, Hinkel and Pörtner2022; Philippenko and Le Cozannet, Reference Philippenko and Le Cozannet2023). These measures are coordinated in coastal management, which increasingly is integrated, ecosystem-based and climate-resilient, including risk assessment, watershed management and catchment rehabilitation, sustainable land and water management, coastline protection, adapted to the specific conditions of coastal cities, islands, deltas and marine habitats (Hinkel et al., Reference Hinkel, Aerts, Brown, Jiménez, Lincke, Nicholls, Scussolini, Sanchez-Arcilla, Vafeidis and Addo2018; Bouwer et al., Reference Bouwer, Cheong, Jacot Des Combes, Frölicher, McInnes, Ratter and Rivera-Arriaga2022; Petzold et al., Reference Petzold, Joe, Kelman, Magnan, Mirbach, Nagle Alverio, Nunn and Ratter2023).

Coastal management strategies group around adapting, defending and armouring a coastal area or abandoning or relocating part of it, depending on benefit, cost and risk assessments (Gopalakrishnan et al., Reference Gopalakrishnan, Landry, Smith and Whitehead2016; Kovalevsky and Scheffran, Reference Kovalevsky and Scheffran2022; NOAA, 2023; Sengupta et al., Reference Sengupta, Kovalevsky, Bouwer and Scheffran2023). Several studies focus on coastal adaptation to climate change and sea level (Bongarts Lebbe et al., Reference Bongarts Lebbe, Rey-Valette, Chaumillon, Camus, Almar, Cazenave, Claudet, Rocle, Meur-Férec, Viard, Mercier, Dupuy, Ménard, Rossel, Mullineaux, Sicre, Zivian, Gaill and Euzen2021; Griggs and Reguero, Reference Griggs and Reguero2021) and the institutional adaptive capacity building of Swedish coastal zone management (Storbjörk and Hedrén, Reference Storbjörk and Hedrén2011), others address path dependency in coastal cities of the Asia-Pacific (Nunn et al., Reference Nunn, Smith and Elrick-Barr2021b) and proactive adaptation of rapidly changing coasts (Brown et al., Reference Brown, Naylor and Quinn2017). Some highlight maladaptation of seawalls along island coasts (Nunn et al., Reference Nunn, Klöck and Duvat2021a) and the diffusion of hard protection to coastal erosion and flooding along island coasts in the Pacific and Indian Oceans (Klöck et al., Reference Klöck, Duvat and Nunn2022). In specific small and low-lying island contexts, also land reclamation and island raising are being implemented (Brown et al., Reference Brown, Nicholls, Bloodworth, Bragg, Clauss, Field, Gibbons, Pladaitė, Szuplewski, Watling, Shareef and Khaleel2023).

The diversity of approaches in coastal areas includes internal relocation as an adaptation strategy in Rangiroa Atoll, French Polynesia (Duvat et al., Reference Duvat, Magnan, Goeldner-Gianella, Grancher, Costa, Maquaire, le Cozannet, Stahl, Volto and Pignon-Mussaud2022) and contestation of coastal restoration and risk reduction in Louisiana (Gotham, Reference Gotham2016). To regulate ocean grabbing, a large-scale marine protected area for the sea of Rapa Nui is suggested by Aburto et al. (Reference Aburto, Gaymer and Govan2020). Economically efficient flood protection standards for the Netherlands are considered by Kind (Reference Kind2014). The contribution of Earth observation in coastal climate services for small islands is discussed by Rölfer et al. (Reference Rölfer, Winter, Máñez Costa and Celliers2020). Coastal adaptation planning can use scenario-based stakeholder engagement and preferences in coastal planning (Tompkins et al., Reference Tompkins, Few and Brown2008), stakeholder perception of climate vulnerability detection using Fuzzy Cognitive Mapping (Gray et al., Reference Gray, Gagnon, Gray, O’Dwyer, O’Mahony, Muir, Devoy, Falaleeva and Gault2014) and stakeholder analysis of climate change and water management in the Dongjiang River basin in South China (Yang et al., Reference Yang, Chan and Scheffran2018).

Nature-based solutions

According to the World Conservation Union (IUCN), nature-based solutions (NbS) are defined as “actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human wellbeing and biodiversity benefits” (Cohen-Shacham et al., Reference Cohen-Shacham, Walters, Janzen and Maginnis2016, p. 5). The IPCC focuses on NbS contributions to climate adaptation and mitigation benefits for coastal regions, including synergies with biodiversity protection and ecosystem services. While the carbon-sequestering mitigation role has dominated much of the earlier discussions, NbS contributions to climate adaptation are increasingly emphasised.

Many studies demonstrate that coastal and marine ecosystems, including wetlands and mangroves, have considerable value as carbon sinks in ‘blue carbon’ sequestration and other ecosystem services such as hydrological regulation, coastal protection, biodiversity and contributing to human livelihoods, especially of pastoralists and fishermen (Conant et al., Reference Conant, Cerri, Osborne and Paustian2017; Leifeld and Menichetti, Reference Leifeld and Menichetti2018; Seddon et al., Reference Seddon, Turner, Berry, Chausson and Girardin2019). Mangrove restoration can promote local and national adaptation, depending on the extent and nature of coastlines (Taillardat et al., Reference Taillardat, Thompson, Garneau, Trottier and Friess2020). The global value of coastal wetlands for storm protection is demonstrated by Costanza et al. (Reference Costanza, Anderson, Sutton, Mulder, Mulder, Kubiszewski, Wang, Liu, Pérez-Maqueo, Luisa Martinez, Jarvis and Dee2021), while Schueler (Reference Schueler2017) presents NbS to enhance coastal resilience, and Landry (Reference Landry2011) discusses coastal erosion as a natural resource management problem from an economic perspective. Challenges of NbS in coastal research for coastal engineers are addressed by Scheres and Schüttrumpf (Reference Scheres, Schüttrumpf, Viet, Xiping and Tung2020) and socioecological impacts of coastal flood mitigation by Inácio et al. (Reference Inácio, Karnauskaitė, Mikša, Gomes, Kalinauskas, Pereira, Ferreira, Kalantari, Hartmann and Pereira2020).

Examples of regional perspectives address flood risk management using NbS in Nouakchott, Mauritania (Senhoury et al., Reference Senhoury, Niang, Diouf, Thomas, Renaud, Sudmeier-Rieux, Estrella and Nehren2016), coastal protection on the Islands of Amrum and Föhr in the North Frisian Wadden Sea (Jordan et al., Reference Jordan, Döring, Fröhle and Ratter2023), and ecosystem-based urban climate change adaptation and wellbeing in Kiribati, Samoa and Vanuatu (Kiddle et al., Reference Kiddle, Bakineti, Latai-Niusulu, Missack, Pedersen Zari, Kiddle, Chanse, Blaschke and Loubser2021). Capacity building on ecosystem-based adaptation helps to cope with extreme events and sea level rise. It increases coastal resilience to extreme weather events and sea level rise on the Uruguayan coast (Carro et al., Reference Carro, Seijo, Nagy, Lagos and Gutiérrez2018). Here, a participatory process involved the community and institutional stakeholders in selecting and prioritising adaptation measures, including soft measures (green infrastructure) such as revegetation with native species, dune regeneration, sustainable drainage systems and reducing use pressures.

Community-based adaptation

Adaptation to climate risk can also build on and promote community resilience. For example, many coastal and small island communities are place-based communities – that is, depending on the local environment to secure their livelihoods – and have traditional and local knowledge that makes them adaptable to environmental changes (Kelman, Reference Kelman2010; Hiwasaki et al., Reference Hiwasaki, Luna and Marçal2015). Dense social networks and strong place attachment in such communities may also contribute to their adaptability to environmental change (Petzold and Ratter, Reference Petzold and Ratter2015; Carmen et al., Reference Carmen, Fazey, Ross, Bedinger, Smith, Prager, McClymont and Morrison2022). Accordingly, there is a move from top-down approaches to community-based adaptation (CbA) approaches, for example, in SIDS (McNamara et al., Reference McNamara, Clissold, Westoby, Piggott-McKellar, Kumar, Clarke, Namoumou, Areki, Joseph, Warrick and Nunn2020).

Examples of CbA in coastal areas are collective coastal afforestation in Bangladesh (Rawlani and Sovacool, Reference Rawlani and Sovacool2011) or communal water resource management, agricultural management and disaster risk community action plans in Vanuatu (Clarke et al., Reference Clarke, McNamara, Clissold and Nunn2019). However, besides the suggested advantages of CbA as a locally led and context-specific form of adaptation, there have always been concerns in the literature regarding responsibilities and representation, effectiveness regarding larger-scale issues, and barriers to long-term success (Forsyth, Reference Forsyth2013; Piggott-McKellar et al., Reference Piggott-McKellar, McNamara, Nunn and Watson2019; Westoby et al., Reference Westoby, McNamara, Kumar and Nunn2020).