Editing IPCC:AR6/WGII/Chapter-10 (section)

===== 10.4.6.3.4 Sea level rise and coastal flooding =====

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Global assessments identify Asia as the most exposed region to SLR (see Section [https://www.ipcc.ch/chapter/10#CCP2.2 CCP2.2.1] ) in terms of the number of people living in low-elevation coastal zones and the number of people exposed to flooding from 1-in-100-years storm surge events ( [[#Neumann--2015|Neumann et al., 2015]] ; [[#Jevrejeva--2016|Jevrejeva et al., 2016]] ; [[#Kulp--2019|Kulp and Strauss, 2019]] ; [[#Abadie--2020|Abadie et al., 2020]] ; [[#Haasnoot--2021|Haasnoot, 2021]] ). Twelve of the top 20 countries exposed to SLR and associated flood events are in Asia, and of these, China, India, Bangladesh, Indonesia and Vietnam are estimated to have the highest total coastal population exposure ( [[#Neumann--2015|Neumann et al., 2015]] ; [[#Edmonds--2020|Edmonds et al., 2020]] ). Critically, regardless of the emissions scenario, 70% of the global population exposed to SLR and land subsidence are in eight Asian countries: China, Bangladesh, India, Vietnam, Indonesia, Thailand, the Philippines and Japan ( [[#Kulp--2019|Kulp and Strauss, 2019]] ). This is particularly worrisome since in highly populated low-lying coastal cities across Asia, it is estimated that land subsidence could be as influential as climate-induced SLR over the 21st century ( [[#Cao--2021|Cao et al., 2021]] ; [[#Nicholls--2021|Nicholls et al., 2021]] ). In East Asia and the Asia–Pacific in general (expected to see 0.2–0.5 m SLR), without adaptation, 1 million people (range of 0.3–2.2 million) are projected to be affected by submergence under RCP8.5 by 2095. Limiting warming will reduce this risk, and under RCP4.5, these numbers of people at risk will be reached by 2140. However, continuing on RCP8.5 increases risk exposure to 7 million (estimated range of 2–24 million people) ( [[#Haasnoot--2021|Haasnoot, 2021]] ). Notably, assuming present-day population and adaptation (in the form of existing protection standards), East and South Asia already have a large number of people at risk of a 1-in-100-years flooding event (63 million) because of relatively lower flood protection (except in China and Malaysia).

These global scenarios will have significant impacts on national and subnational populations. For example, in Bangladesh, under 0.44 and 2 m mean SLR, direct inundation is estimated to drive migration of 0.73–2.1 million people by 2100 ( [[#Davis--2018|Davis et al., 2018]] ). Such migration will have direct development implications: for example, destination locations could see additional demands on jobs (594,000), housing (197,000) and food (783 × 10 9 calories) by mid-century as a result of those displaced by SLR ( [[#Davis--2018|Davis et al., 2018]] ).

Among the 20 largest coastal cities with the highest flood losses by 2050, 13 are in Asia [[#footnote-008|5]] , with a regional concentration in South, Southeast and East Asia ( [[#Hallegatte--2013|Hallegatte et al., 2013]] ). Furthermore, 9 of these cities (Guangzhou, Kolkata, Tianjin, Ho Chi Minh City, Jakarta, Zhanjiang, Bangkok, Xiamen, Nagoya) also have an additional risk of subsidence due to SLR and flooding ( [[#Hallegatte--2013|Hallegatte et al., 2013]] ). Guangzhou, China, is estimated to be the most economically vulnerable city in the world to SLR by 2050, with estimated losses of 254 million USD yr –1 under 0.2 m SLR ( [[#Jevrejeva--2016|Jevrejeva et al., 2016]] ). With a 2°C warming, Guangzhou is expected to see SLR of 0.34 m; under 5°C warming, this number would rise to 1.93 m. A more recent estimate calculates expected damage in Guangzhou due to SLR under RCP8.5 to reach 331 billion USD by 2050 and 420 billion USD under the high-end scenario with figures doubling by 2070. By 2100, expected damage could reach 1.4 trillion USD under RCP8.5 and 1.8 trillion USD under the high-end scenario. Similarly, in Mumbai (India) SLR damages amount to US$ 112–162 billion by 2050 and could increase by a factor of 2.8–2.9 by 2070 ( [[#Abadie--2020|Abadie et al., 2020]] ). In coastal cities such as Bangkok and Ho Chi Minh City, projected land subsidence rates, mainly due to excessive groundwater extraction, are comparable to, or exceed, expected rates of SLR, resulting in an additional 0.2 m SLR by 2025 ( [[#Jevrejeva--2016|Jevrejeva et al., 2016]] ). In Shanghai, current annual damage by coastal inundation is estimated at 0.03% of local GDP; under RCP4.5, this increases to 0.8% by 2100 (uncertainty range of 0.4–1.4%) and is further exacerbated by land subsidence and socioeconomic development ( [[#Du--2020|Du et al., 2020]] ). It is important to note that these projections assume (a) no adaptation and (b) that damage repairs are undertaken and completed annually. Given these assumptions, while these estimates communicate the scale of projected impacts, they are indicators of possible damages in the absence of adaptation and ''not'' actual projections.

The SLR affects economic growth, its drivers and welfare outcomes ( [[#Hallegatte--2012|Hallegatte, 2012]] ; [[#Pycroft--2016|Pycroft et al., 2016]] ; [[#Lee--2020|Lee and Asuncion, 2020]] ) through (a) permanent loss of land and natural capital, (b) loss of infrastructure and physical capital, (c) loss of social capital and migration, (d) temporary floods, food insecurity and loss of livelihoods and (e) added expenditure for coastal protection. Without adaptation, direct damage to the GDP by 2080 due to SLR would be highest in Asia ( ''robust evidence, medium agreement'' ), with China losing between 64.2 billion USD (under A1B of 2.4°C by the 2050s and 3.8°C by the 2090s at 0.47 m), 95.8 billion USD (under the RAHM scenario of 1.4 m SLR by 2100 at 1.12 m) and 118.4 billion USD (at a high SLR of 2 m by 2100 at 1.75 m) in direct damages, and an additional 5.7, 4.5 and 4.5 billion USD, respectively, due to migration ( [[#Pycroft--2016|Pycroft et al., 2016]] ). Closely after China will be India, the Republic of Korea, Japan, Indonesia and Russia. Overall, Asia can experience direct losses of about 167.6 billion USD (at 0.47 m), 272.3 billion USD (at 1.12 m) or 338.1 billion USD (at 1.75 m), and an additional 8.5, 24 or 15 billion USD at the respective SLR projections, due to migration [[#footnote-007|6]] .

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