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

=== 4.6.7 Adaptation Responses for Water-Related Conflicts ===

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AR5 concluded with ''high confidence'' that challenges for adaptation actions (though not water) are particularly high in regions affected by conflicts ( [[#Field--2014a|Field et al., 2014a]] ). Although climate–conflict linkages are disputed ( [[#4.3.6|Section 4.3.6]] ), the potential for synergies between conflict risk reduction and adaptation to climate change exists ( [[#Mach--2019|Mach et al., 2019]] ). For example, discourses around climate–conflict inter-linkages can present opportunities for peace building and cooperation ( [[#Matthew--2014|Matthew, 2014]] ; [[#Abrahams--2020|Abrahams, 2020]] ). Indeed, adaptation efforts are needed in the context of conflict, where the pre-existing vulnerability undermines the capacity to manage climatic stresses. In addition, adaptive capacity depends on contextual factors such as power relations and historical, ethnic tensions ( [[#Petersen-Perlman--2017|Petersen-Perlman et al., 2017]] ; [[#Eriksen--2021|Eriksen et al., 2021]] ), which need to be adequately considered in the design of adaptation strategies.

Some adaptation options, such as water conservation, storage and infrastructure, voluntary migration, planned relocation due to flood risk/sea level rise, and international water treaties, can reduce vulnerability to climate change and conflicts. However, on the other hand, these adaptation options sometimes may have unintended consequences by increasing existing tensions ( [[#Milman--2014|Milman and Arsano, 2014]] ); displacing climate hazards to more vulnerable and marginalised groups ( [[#Milman--2014|Milman and Arsano, 2014]] ; [[#Mach--2019|Mach et al., 2019]] ), for example, pastoralists ( [[#Zografos--2014|Zografos et al., 2014]] ); and favouring some over others, such as industry over agriculture (Iglesias and Garrote, 2015)¸ upstream countries over downstream countries ( [[#Veldkamp--2017|Veldkamp et al., 2017]] ), and men over women ( [[#Chandra--2017|Chandra et al., 2017]] ). Such unintended consequences may happen when adaptation measures intended to reduce vulnerability produce maladaptive outcomes by rebounding or shifting vulnerability to other actors ( [[#Juhola--2016|Juhola et al., 2016]] ). For example, in the Mekong River basin, the construction of dams and water reservoirs contributes to the adaptation efforts of the upstream Southeast Asia countries while increasing current/future vulnerability to floods and droughts in downstream countries and can emerge as a cause of conflict ( [[#Earle--2015|Earle et al., 2015]] ; [[#Ngô--2016|Ngô et al., 2016]] ).

Furthermore, adaptation in the context of water-related conflicts is also constrained by economic, institutional and political factors, competition for development ( [[#Anguelovski--2014|Anguelovski et al., 2014]] ) and gender considerations ( [[#Sultana--2014|Sultana, 2014]] ; [[#Chandra--2017|Chandra et al., 2017]] ), which need to be taken into account when designing adaptation plans/measures.

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'''Box 4.5 | Reduce, Remove, Reuse and Recycle (4Rs): Wastewater Reuse and Desalination as an Adaptation Response'''
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Circular economies can increase the available sustainable adaptation space by moving away from a linear mode of production of ‘extract-produce-use-discard’ to a ‘4Rs’ closed loop to reduce pollution at the source, remove contaminants from wastewater, reuse treated wastewater and recover valuable by-products ( [[#UN%20Water--2017|UN Water, 2017]] ; see WGIII 11.3.3).

It is estimated that 380 billion m 3 of wastewater is produced annually worldwide, which equals about 15% of agricultural water withdrawals. The recovery of nitrogen, phosphorus and potassium from wastewater can offset 13.4% of the global agriculture demand for these nutrients ( [[#Jiménez--2008|Jiménez and Asano, 2008]] ; [[#Fernández-Arévalo--2017|Fernández-Arévalo et al., 2017]] ). Recycling human waste worldwide could satisfy an estimated 22% of the global demand for phosphorus ( [[#UN%20Water--2017|UN Water, 2017]] ). It has been estimated that some 36 million ha worldwide (some 12% of all irrigated land) reuse urban wastewater, mainly for irrigation. However, only around 15% is adequately treated ( [[#Thebo--2017|Thebo et al., 2017]] ), thus the need to invest in sustainable, low-cost wastewater treatment to protect public health. The irrigation potential of this volume of wastewater stands at 42 million ha. Wastewater production is expected to increase globally to 574 billion m 3 by 2050, a 51% increase compared to 2015, mainly due to a growing urban population ( [[#Qadir--2020|Qadir et al., 2020]] ). Water reuse with treated wastewater for potable and non-potable purposes can be practised in a manner that is protective of public health and the environment ( [[#WHO--2006|WHO, 2006]] ; [[#WHO--2017|WHO, 2017]] ). For example, when implemented with sufficient treatment standards, the use of recycled water for the irrigation of crops is protective of public health ( [[#Blaine--2013|Blaine et al., 2013]] ; [[#Paltiel--2016|Paltiel et al., 2016]] ), as was determined by an appointed panel of experts in the state of California ( [[#Cooper--2012|Cooper et al., 2012]] ). However, there are several barriers to the adoption of wastewater reuse; these include technical barriers and public health aspects related to microbiological and pharmaceuticals risks ( [[#Jiménez--2008|Jiménez and Asano, 2008]] ; [[#Jaramillo--2017|Jaramillo and Restrepo, 2017]] ; [[#Saurí--2019|Saurí and Arahuetes, 2019]] ). These are currently being addressed by strengthening regulatory standards, with, for example, 11 out of 22 Arab States adopting legislation permitting the use of treated wastewater ( [[#WHO--2006|WHO, 2006]] ; [[#US%20EPA--2017|US EPA, 2017]] ; [[#WHO--2017|WHO, 2017]] ; [[#EC--2020|EC, 2020]] ). Benefits of wastewater reuse usually outweigh the costs ( [[#Stacklin--2012|Stacklin, 2012]] ; [[#Hernández-Sancho--2015|Hernández-Sancho et al., 2015]] ; [[#UN%20Water--2017|UN Water, 2017]] ).

Desalination is particularly important in arid and semiarid climates, coastal cities and small island states (Box 4.2). There were 16,000 operational desalination plants globally in 2017, with a daily desalinated water production of 95 million m 3 d -1 ( [[#IDA--2020|IDA, 2020]] ). In 2012, desalinated water was equivalent to 0.6% of the global water supply, and 75.2 TWh of energy per year was used to generate desalinated water; in other words, about 0.4% of the worldwide electricity consumption ( [[#IRENA--2012|IRENA, 2012]] ). Unfortunately, only 1% of total desalinated water uses renewable sources ( [[#IRENA--2012|IRENA, 2012]] ; [[#Amy--2017|Amy et al., 2017]] ; [[#Balaban--2017|Balaban, 2017]] ; [[#Martínez-Alvarez--2018a|Martínez-Alvarez et al., 2018a]] ; [[#Jones--2019|Jones et al., 2019]] ) ( [[#4.7.6|Section 4.7.6]] ). Desalination has already helped to meet urban and peri-urban water supply, particularly during annual or seasonal drought events, with half of the world’s desalination capacity in the Arab region ( [[#UN%20Environment--2019|UN Environment, 2019]] ; [[#UN%20Water--2021|UN Water, 2021]] ). In addition, seawater desalination could help address water scarcity in 146 (50%) large cities (including 12 (63.2%) megacities) ( [[#He--2021|He et al., 2021]] ). Desalination is also being adopted for irrigation. For example, in the island of Gran Canary (Spain), 30% of the agricultural surface area is irrigated with desalinated water to irrigate high-value crops ( [[#Burn--2015|Burn et al., 2015]] ; [[#Martínez-Alvarez--2018a|Martínez-Alvarez et al., 2018a]] ; [[#Monterrey-Viña--2020|Monterrey-Viña et al., 2020]] ). The expected growth of desalination, if not coupled with renewable energy (RE), causes a projected 180% increase in carbon emissions by 2040 ( [[#GCWDA--2015|GCWDA, 2015]] ; [[#Pistocchi--2020|Pistocchi et al., 2020]] ). There have been advances in large-scale and on-farm renewable desalination ( [[#Abdelkareem--2018|Abdelkareem et al., 2018]] ). Using renewable energy to decarbonise desalination has meant that the projected global average levelled cost of water could decrease from €2.4 m –3 (2015) to approximately €1.05 m –3 by 2050, considering unsubsidised fossil fuel costs ( [[#Caldera--2020|Caldera and Breyer, 2020]] ). Desalination will be maladaptive if fossil fuel is used ( [[#Tubi--2021|Tubi and Williams, 2021]] ).

In summary, a resilient circular economy is central to deliver access to water and sanitation, with, wastewater treatment, desalination and water reuse as viable adaptation options compatible with the Paris Agreement, while safeguarding ecological flows according to the SDG6 targets for climate resilient development ( ''medium evidence, high agreement'' ).

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'''Box 4.6 | Nature-based Solutions for Water-Related Adaptation'''
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In the context of climate change-induced water insecurity, nature-based solutions (NbS) are an adaptation response that relies on natural processes to enhance water availability and water quality and mitigate risks associated with water-related disasters while contributing to biodiversity ( [[#IUCN--2020|IUCN, 2020]] ).

Until recently, NbS have been considered mainly for mitigation ( [[#Kapos--2020|Kapos et al., 2020]] ; [[#Seddon--2020|Seddon et al., 2020]] ). Yet, NbS increase the low-cost adaptation options that expand the adaptation space due to their multiple co-benefits (Cross-Chapter Box NATURAL in Chapter 2). Furthermore, a meta-review of 928 NbS measures globally shows that NbS largely addresses water-related hazards like heavy precipitation (37%) and drought (28%) ( [[#Kapos--2020|Kapos et al., 2020]] ).

Natural infrastructure (green and blue) uses natural or semi-natural systems, for example, wetlands, healthy freshwater ecosystems, etc., to supply clean water, regulate flooding, enhance water quality and control erosion (6.3.3.1 to 6.3.3.6.). Grey infrastructure can damage biophysical and hydrological processes, seal soils and bury streams. Compared with grey physical infrastructure, natural infrastructure is often more flexible, cost-effective and can provide multiple societal and environmental benefits simultaneously ( [[#McVittie--2018|McVittie et al., 2018]] ; [[#UN%20Water--2018|UN Water, 2018]] ; [[#IPBES--2019|IPBES, 2019]] ). There is increasing evidence and assessment methods on the role of NbS for climate change adaptation and disaster risk reduction at different scales ( [[#Chausson--2020|Chausson et al., 2020]] ; [[#Seddon--2020|Seddon et al., 2020]] ; [[#Cassin--2021|Cassin and Matthews, 2021]] ) ( [[#4.6.5|Section 4.6.5]] ).

At the landscape scale, there is evidence that impacts from fluvial and coastal floods can be mitigated through water-based NbS like detention/retention basins, river restoration and wetlands ( [[#Thorslund--2017|Thorslund et al., 2017]] ; [[#Debele--2019|Debele et al., 2019]] ; [[#Huang--2020|Huang et al., 2020]] ). Several examples show the effectiveness of floodplain restoration, natural flood management and making room for the river measures (see FAQ2.5, [[#Hartmann--2019|Hartmann et al., 2019]] ; [[#Mansourian--2019|Mansourian et al., 2019]] ; [[#Wilkinson--2019|Wilkinson et al., 2019]] ) ( ''medium evidence, high agreement'' ). Likewise, the use of managed aquifer recharge (MAR) in both urban and rural settings will be crucial for groundwater-related adaptation ( [[#Zhang--2020|Zhang et al., 2020]] a).

At the urban and peri-urban scale, the use and effectiveness of NbS is a crucial feature to build resilience in cities for urban stormwater management and heat mitigation ( [[#Depietri--2017|Depietri and McPhearson, 2017]] ; [[#Carter--2018|Carter et al., 2018]] ; [[#Huang--2020|Huang et al., 2020]] ; [[#Babí%20Almenar--2021|Babí Almenar et al., 2021]] ) ( ''high confidence'' ). NbS have been used for stormwater management by combining water purification and retention functions ( [[#Prudencio--2018|Prudencio and Null, 2018]] ; [[#Oral--2020|Oral et al., 2020]] ). NbS have also been used to mitigate impacts from high-impact extreme precipitation events by integrating large-scale NbS investment plans into urban planning in cities like New York and Copenhagen, highlighting the importance of blended finance and investment (including insurance) to mainstream NbS investments ( [[#Liu--2017|Liu and Jensen, 2017]] ; [[#Rosenzweig--2019|Rosenzweig et al., 2019]] ; [[#Lopez-Gunn--2021|Lopez-Gunn et al., 2021]] ). According to the CDP database, one in three cities use NbS to address climate hazards, and this trend is growing ( [[#Kapos--2020|Kapos et al., 2020]] ).

NbS are cost-effective and can complement or replace grey solutions (Cross-Chapter Box FEASIB in Chapter 18, 3.2.3) ( [[#Chausson--2020|Chausson et al., 2020]] ). Moreover, estimates of NbS are increasingly based on integrated economic valuations that incorporate co-design with stakeholders to incorporate LK ( [[#Pagano--2019|Pagano et al., 2019]] ; [[#Giordano--2020|Giordano et al., 2020]] ; [[#Hérivaux--2021|Hérivaux and Le Coent, 2021]] ; [[#Palomo--2021|Palomo et al., 2021]] ) ( ''medium evidence, high agreement'' ). Yet, the performance of NbS themselves may be limited at higher GWLs ( [[#Calliari--2019|Calliari et al., 2019]] ; [[#Morecroft--2019|Morecroft et al., 2019]] ).

More knowledge is needed on the long-term benefits of NbS, particularly to hydro-meteorological hazards ( [[#Debele--2019|Debele et al., 2019]] ). There is still ''low evidence'' for slow-onset events, including the applicability of NbS to manage highly vulnerable ecosystems and in agriculture (Sonneveld, 2018),

In summary, there is growing evidence on NbS effectiveness as an adaptation measure and its critical role for transformative adaptation to address climate change water-related hazards and water security ( ''medium evidence, high agreement'' ). Moreover, several NbS– —for example, natural (blue and green) and grey infrastructure—can help address water-related hazards such as coastal hazards, heavy precipitation, drought, erosion and low water quality ( ''high confidence'' ).

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