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

==== 10.4.4.5 Climate Vulnerability and Adaptation: Interfaces and Interventions ====

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In Asia and its diverse sub-regions, the challenge of adaptation to climate change at diverse sectors, sites and scales of vulnerability in the domain of freshwater resources is compounded by the nexus between long-standing non-climatic vulnerabilities and climatic impacts, both observed and projected. Water insecurities in Asia are increasing due to excessive freshwater withdrawals ( [[#Satoh--2017|Satoh et al., 2017]] ), economic and population growth ( [[#Gleick--2018|Gleick and Iceland, 2018]] ), urbanisation and peri-urbanisation ( [[#Roth--2019|Roth et al., 2019]] ), food insecurity ( [[#Demin--2014|Demin, 2014]] ) and lack of access to clean and safe drinking water ( [[#Cullet--2016|Cullet, 2016]] ), which mostly affects the health of the most vulnerable members of society.

Significantly, climate change will add to already existing vulnerabilities. In the case of the Yellow River basin in China, underlining the interface between future water scarcity and hydroclimatic and anthropogenic drivers, a recent study expects moderate-to-severe water scarcity over six Yellow River sub-catchments under the RCP4.5 scenario, and anticipates that human influences on water scarcity will be worse than that of climate change, with water availability in the downstream being impacted by concurrent changes in land use and high temperature ( [[#Omer--2020|Omer et al., 2020]] ). Nearly 8% of internationally shared or transboundary aquifers (TBAs), ensuring livelihood security for millions of people through sustaining drinking water supply and food production, are currently overstressed due to human overexploitation ( [[#Wada--2013|Wada and Heinrich, 2013]] ). The Asia Pacific region has the highest annual water withdrawal due to its geographic size, growing population and irrigation practices, and water for agriculture continues to consume 80% of the region’s resources ( [[#Taniguchi--2017b|Taniguchi et al., 2017b]] ; [[#Visvanathan--2018|Visvanathan, 2018]] ).

In South Asia, surface water and groundwater resources are already under stress (both in terms of quality and quantity) due to population growth, economic development, poor governance and management, and poor efficiency of use in economic production. In the past 40 years, there has been an increasing reliance on groundwater in South Asia for irrigation ( [[#Rodell--2009|Rodell et al., 2009]] ; [[#Tiwari--2009|Tiwari et al., 2009]] ; [[#Surie--2015|Surie and Prasai, 2015]] ; [[#Bhanja--2016|Bhanja et al., 2016]] ; [[#Shrestha--2016|Shrestha et al., 2016]] ; [[#Mukherjee--2018|Mukherjee, 2018]] ; [[#Shah--2018|Shah et al., 2018]] ). It is noteworthy that India, Bangladesh, Pakistan and China together account for more than 50% of the world’s groundwater withdrawals ( [[#Scott--2019|Scott et al., 2019]] ). A study conducted in the Shahpur and Maner districts of Bihar, India, in which drinking water sourced from the groundwater of 388 households was tested, showed that 70–90% of the sampled household’s drinking water contained either arsenic or iron, or both ( [[#Thakur--2019|Thakur and Gupta, 2019]] ). Given the nexus between CIDs and non-climate drivers, an effective adaptation to the impacts of climate change would also demand sustainable development and management of shared aquifer resources, which in turn require reliable TBA inventories and improved knowledge production and knowledge sharing on the shared groundwater systems ( [[#Lee--2018a|Lee et al., 2018a]] ).

A study of peri-urban spaces involving four South Asian cities, Khulna (Bangladesh) ( [[#Pervin--2020|Pervin et al., 2020]] ), Gurugram and Hyderabad (India), and Kathmandu (Nepal), has shown the nexus between intensifying use and deteriorating quality of water and the impact of climate change, resulting in peri-urban water insecurity and conflict ( [[#Roth--2019|Roth et al., 2019]] ). The challenge of ensuring access to water resources and their (re)allocation and prioritisation for marginalised communities remains on the agenda of policy-oriented interdisciplinary research and demands effective implementation of its findings at the grassroots level by the administrative agencies. Taking water security as a key CCA goal at the urban-city scale of Bangkok, a study ( [[#Babel--2020|Babel et al., 2020]] ) has shown the usefulness of a generic framework with 5 dimensions, 12 indicators and a set of potential variables to support national-level initiatives and plans in diverse climatic and socioeconomic conditions across various sub-regions of Asia.

In the Kathmandu valley in Nepal, where groundwater resources are under immense pressure from multiple stresses, including overextraction and climate change, mapping groundwater resilience to climate change has been demonstrated as a useful tool to understand the dynamics of groundwater systems, and thereby facilitate the development of strategies for sustainable groundwater management ( [[#Shrestha--2020|Shrestha et al., 2020]] ).

In the Mekong Delta, the groundwater storage is projected to decline by more than 120 and 160 million m 3 under RCP4.5 and RCP8.5 scenarios, respectively, by the end of the 21st century, in conjunction with land subsidence and SLR. This in turn calls for proactive planning and implementation of adaptation strategies that address multiple stresses in order to ensure sustainable utilisation of groundwater resources in the Mekong Delta in the context of future climatic conditions and associated uncertainties ( [[#Wang--2021a|Wang et al., 2021a]] ). Proposed CCA strategies for the Mekong River basin include a better understanding of the complex linkages between climate change, technological interventions, land-use change, water-use change and socioeconomic developments both in the upstream and downstream riparian countries ( [[#Evers--2018|Evers and Pathirana, 2018]] ).

While South Asian countries have done well in attaining Goal 6 of Sustaining Development Goals, access to safe and clean drinking water remains a challenge. Taking Indian rivers as an example, it is suggested that participatory river protection and rehabilitation, based on comprehensive knowledge of the river-system dynamics, and local awareness at the community level, may act as a multiplier for river conservation measures ( [[#Nandi--2016|Nandi et al., 2016]] ).

Hydroclimatic extremes in the HKH region could adversely impact the Ganga, Brahmaputra and Meghna basins ( [[#Wijngaard--2017|Wijngaard et al., 2017]] ; [[#Acharya--2019|Acharya and Prakash, 2019]] ). Studies have recommended watershed or basin analysis to address the challenge of adaptation in urban spaces ( [[#Lele--2018|Lele et al., 2018]] ). A study of northern Bangladesh that focused on encouraging traditional ways of cultivation suggests that rural women have Indigenous knowledge and their participation can play a useful role ( [[#Kanak%20Pervez--2015|Kanak Pervez et al., 2015]] ). The knowledge pertains to agriculture, soil conservation, fish and animal production, irrigation and water conservation. There has also been a focus on gendered construction of local flood-forecasting knowledge in rural communities in India living in the Gandak River basin ( [[#Acharya--2019|Acharya and Prakash, 2019]] ). While designing the adaptation options, understanding the water–energy–food (WEF) nexus among different water-use sectors is crucial ( [[#10.5.3|Section 10.5.3]] ). Understanding of the WEF nexus could be beneficial for achieving water security in developing countries in Asia ( [[#Nepal--2019|Nepal et al., 2019]] ).

AR5 identified a number of adaptation challenges and options facing the stakeholders in the wake of climate-change-induced vulnerabilities, uncertainties and risks in the freshwater sector, and underlined the importance of an integrated management approach as well as acknowledging diverse socioeconomic contexts, differentiated capacities and the uneven pace of impacts. Further validated by recent research in terms of their usefulness, these adaptation options include building and improving capital-intensive physical water infrastructure such as irrigation channels, flood-control dams and water storage ( [[#Nüsser--2017|Nüsser and Schmidt, 2017]] ). Drawing upon customary institutions and combining Indigenous knowledge systems with scientific knowledge, innovative structures, including artificial glaciers, ice stupas and snow barrier bands, have been built by local communities in Ladakh, Zanskar and Himachal Pradesh in India ( [[#Hock--2019|Hock et al., 2019]] ; [[#Nüsser--2019|Nüsser et al., 2019]] ). Communities in Solukhumbu, Nepal, in response to depleting water flow in snow-fed rivers, have chosen adaptation through changing practices by collecting water from distant sources for domestic consumption ( [[#McDowell--2013|McDowell et al., 2013]] ). Taking the IPCC concept of climate risk as a basis for adaptation planning, a pilot study of flood risk in Himachal Pradesh, India ( [[#Allen--2018|Allen et al., 2018]] ), integrating assessment of hazard, vulnerability and exposure in the complementary domains of CCA and DRR, has identified stakeholder consultation, knowledge exchange and institutional capacity building as key steps in adaptation planning. Aquifer storage and recovery has been proposed as an ‘alternative climate-proof freshwater source’ for deltaic regions in Asia, particularly those with a history of saline groundwater aquifers ( [[#Hoque--2016|Hoque et al., 2016]] ). It is further argued ( [[#Hadwen--2015|Hadwen et al., 2015]] ) that water, sanitation and hygiene objectives would need to be addressed as a component of a wider integrated water resource management (IWRM) framework.

Ensuring sustainability of the rivers and ecosystems requires coordinated and collaborative action on the part of all countries, with the long-term goal of synergising political, social, cultural and ecological facets associated with the riverine system. Daunting as this challenge is, evidence suggests that a long-term view of transboundary basins is not very optimistic as big rivers of Asia contribute heavily towards urban and agricultural activities, and are experiencing challenges of increasing sedimentation, large-scale damming and pollution, among others ( [[#Best--2018|Best, 2018]] ). In the case of China, [[#Sun--2016|Sun et al. (2016)]] have shown that the localised vulnerabilities within the Yangtze River basin prompt an ‘integrated basin-wide approach’ that is able to account for the specific needs of each of its sub-basins.

In HMA, factors that undermine effective adaptation to climate change include both sudden-onset and slow-paced disasters along with the knowledge deficit regarding cryospheric change and its adverse impacts on water resources and also the agriculture and hydropower sectors. Other key barriers include a sectoral approach, overemphasis on structural approaches and the lack of context-sensitive, community-centric understanding of how these changes influence perceptions, options and decisions about migration, relocation and resettlement ( [[#Rasul--2020|Rasul et al., 2020]] ; [[#Hock--2019|Hock et al., 2019]] ). More interdisciplinary research is needed on highly precarious future pathways and the intersection between CIDs and non-climate drivers in order to anticipate and mitigate diverging and uncertain outcomes.

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'''Box 10.4 | Case Study on Climate Vulnerability and Cross-Boundary Adaptation in Central Asia'''
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In Central Asia, water scarcity has been ranked in the top five global risks ( [[#Gleick--1993|Gleick, 1993]] ; [[#Zhupankhan--2018|Zhupankhan et al., 2018]] ). Cross-boundary adaptation remains critically important in this region with abundant glaciers in the Pamir Plateau of Tajikistan ( [[#Hu--2017|Hu et al., 2017]] ) and areas with severe glacier retreat in the Tianshan Mountains ( [[#Liu--2015|Liu and Liu, 2015]] ). The spatial variations of glacier and other climate variables have added to uncertainty related to the dynamic of the water cycle. The headwater regions, such as Pamir area, would be significantly affected by the climate parameters, such as the stronger rainfall intensity, more frequent rainfall and higher temperature ( [[#Luo--2019|Luo et al., 2019]] ). The water resources in the Pamir Plateau will range from −0.48 to 5.6% ( [[#Gulakhmadov--2020|Gulakhmadov et al., 2020]] ), and the crop phenological period in Tajikistan and Kyrgyzstan will be about 1–2 weeks earlier. The threat of agricultural water stress is increasing as well. The oasis in downstream areas will face more complex water resource fluctuations, water crisis and desertification. In particular, rain-fed agriculture in northern Kazakhstan, Uzbekistan and western Turkmenistan is particularly dependent on water resources. Under the RCP2.6 and RCP4.5 scenarios, considering CO 2 fertilisation effects and land-use projections, the increase in CO 2 atmospheric concentration and accumulated temperature can contribute to a 23% increase in cotton yield in Central Asia ( [[#Tian--2019|Tian and Zhang, 2019]] ), but extreme climate, such as drought, heatwaves and rainstorms, will have a 10% negative impact on agricultural production and the ecological environment ( [[#Zhang--2017|Zhang and Ren, 2017]] ). High-efficiency water-saving technology will help the upstream and downstream water resource management in Central Asian countries to adapt to the variation in water resources quantity, frequency and spatial pattern.

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