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

===== 10.4.6.3.2 Extreme temperatures and heatwaves =====

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Urbanisation and climate change interact to drive an urban heat island (UHI) effect across Asian cities ( [[#Hauck--2016|Hauck et al., 2016]] ; [[#Chapman--2017|Chapman et al., 2017]] ; also see Figure 6.4 in Chapter 6). Three regions which are expected to see higher maximum wet-bulb temperature than global averages are southwest Asia around the Persian Gulf and Red Sea, South Asia in the Indus and Ganges river valleys, and eastern China ( [[#Im--2017|Im et al., 2017]] ; Perkins-Kirkpatrick et al., 2020).

Impacts of heatwaves at 1.5°C and 2°C in cities are substantially larger than under the present climate ( [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ). In South Asia particularly, more intense heatwaves of longer durations and occurring at a higher frequency are projected with ''medium confidence'' over India ( [[#Murari--2015|Murari et al., 2015]] ) and Pakistan (IPCC AR6, WGI, Table 11.5; [[#Ali--2018|Ali et al., 2018]] ; [[#Nasim--2018|Nasim et al., 2018]] ; [[#Ali--2020|Ali et al., 2020]] ; [[#IPCC--2021|IPCC, 2021]] ). At the city level, these projections could translate into significant impacts: at 1.5°C, on average, every year Kolkata will experience heat equivalent to the 2015 record heatwaves; Karachi about once every 3.6 years; and under 2°C warming, both regions could expect such heat annually ( [[#Matthews--2017|Matthews et al., 2017]] ). In Pakistan, Hyderabad is ''likely'' to be the hottest city by 2100 with the highest average temperature reaching 29.9°C (RCP4.5) to 32°C (RCP8.5) followed by Jacobabad, Bahawalnagar and Bahawalpur cities ( [[#Ali--2020|Ali et al., 2020]] ). The frequency of heatwave days (HWF) will increase by 22.8, 22.3 and 26.5 d yr –1 in northern, eastern and western Japan, respectively, with megacities such as Tokyo, Osaka and Nagoya seeing large increases in HWF and related deaths ( [[#Nakano--2013|Nakano et al., 2013]] ).

In China’s urban agglomerations, an increase in the global warming from 1.5°C to 2°C is ''likely'' to exacerbate the intensity of extreme maximum temperature 4.1 times ( [[#Yu--2018d|Yu et al., 2018d]] ). From 1995 to 2014 China’s urban agglomerations (Beijing–Tianjin–Hebei, Yangtze River Delta, Middle Yangtze River, Chongqing–Chengdu and Pearl River Delta) experienced no more than three heat danger d yr –1 , which is projected to increase to 3–13 d by 2041–2060 and 8–67 d by 2081–2100 under high-emissions shared socioeconomic pathways SSP3-7.0 and SSP5-8.5, resulting in approximately 260 million people (19% of the total population of China) and 310 million people (39% of the total population), respectively, facing more than three heat-danger days annually ( [[#Zhang--2021|Zhang et al., 2021]] ). This projected risk exposure is reduced under low-emissions pathways (SSP1-2.6 and SSP2-4.5), where annual heat-danger days will remain similar to current levels or increase slightly ( [[#Zhang--2021|Zhang et al., 2021]] ).

Critically, these projections of higher temperatures will have a significant impact on heat-related morbidity and mortality, labour productivity, mental health, and health and well-being outcomes across all sub-regions of Asia ( ''medium evidence, high confidence'' ) ( [[#Pal--2016|Pal and Eltahir, 2016]] ; [[#Im--2017|Im et al., 2017]] ; [[#Arifwidodo--2019|Arifwidodo et al., 2019]] ; [[#Arshad--2020|Arshad et al., 2020]] ). In West Asia and the North China Plain especially, extreme wet-bulb temperatures are expected to approach, and possibly exceed, the physiological threshold for human adaptability (35°C) ( [[#Pal--2016|Pal and Eltahir, 2016]] ; [[#Kang--2018|Kang and Eltahir, 2018]] ). By the end of the century, under higher projections (RCP8.5), the daily maximum wet-bulb temperature is expected to exceed the survivability threshold across most of South Asia ( [[#Im--2017|Im et al., 2017]] ). City-specific studies articulate what these regional projections will mean for urban populations. For example, at 1.5°C warming, without adaptation, annual heat-related mortality in 27 major cities across China is projected to increase from 32.1 per million inhabitants annually in 1986–2005 to 48.8–67.1 per million. This number increases to 59.2–81.3 per million for 2°C warming ( [[#Wang--2019a|Wang et al., 2019a]] ). In the Republic of Korea, deaths from heat disorders are expected to increase approximately fivefold under the RCP4.5 and 7.2-fold under RCP8.5 by 2060 compared with the current baseline value of ~23 people per summer ( [[#Kim--2016a|Kim et al., 2016a]] ). Importantly, heat exposure is differentiated within cities: it disproportionally affects the poorest populations (Lohrey et al., 2021) and those with lesser access to green spaces ( [[#Arifwidodo--2020|Arifwidodo and Chandrasiri, 2020]] ).

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