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

=== 4.6.2 Adaptation in the Agricultural Sector ===

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AR5 reported a range of available hard and soft adaptation options for water-related adaptation in the agricultural sector. However, the evidence on the effectiveness of these adaptation responses, now and in the future, was not assessed ( [[#Noble--2014|Noble et al., 2014]] ; [[#Porter--2014|Porter et al., 2014]] ). Assessing the feasibility of different irrigation measures as adaptation, SR1.5 ( [[#de%20Coninck--2018|de Coninck et al., 2018]] ) found mixed evidence, depending on the applied methodology.

There is ''high confidence'' that water-related adaptation is occurring in the agricultural sector ( [[#Acevedo--2020|Acevedo et al., 2020]] ; [[#Ricciardi--2020|Ricciardi et al., 2020]] ), and water-related adaptation in the agricultural sector makes up the majority of documented local, regional and global evidence of implemented adaptation ( ''high confidence'' ) ( [[#4.7.1|Section 4.7.1]] , Figure 4.23 and Figure 4.24, Table 4.8). However, while there is increasing evidence of adaptation and its benefits across multiple dimensions, the link between adaptation benefits and climate risk reduction is unclear due to methodological challenges ( ''medium confidence'' ) ( [[#4.7.1|Section 4.7.1]] ). On the other hand, while it is methodologically possible to measure the effectiveness of future adaptation in reducing climate risks, the main limitation here is that not all possible ranges of future adaptations can be modelled given the limitations of climate and impact models ( ''high confidence'' ) ( [[#4.7.2|Section 4.7.2]] ). Furthermore, findings on current adaptation are constrained by what is documented in peer-reviewed articles. At the same time, there may be a range of options implemented on the ground by local governments or as a part of corporate social responsibility that is not published in peer-reviewed publications.

Water and soil conservation measures (e.g., reduced tillage, contour ridges or mulching) are frequently documented as adaptation responses to reduce water-related climate impacts ( [[#Kimaro--2016|Kimaro et al., 2016]] ; [[#Traore--2017|Traore et al., 2017]] ). This measure features in all continents’ top four adaptation responses except Australasia (Figure 4.27). Especially for rain-fed farming, which currently is the norm in most of Africa, large parts of Central and South America and Europe, water and soil conservation measures and various components of conservation agriculture are some of the most frequently used adaptation responses ( [[#Jat--2019|Jat et al., 2019]] ). This measure is deemed to have economic benefits and benefits for vulnerable communities who adopt this measure ( ''high confidence'' ) and benefits in terms of water saving and positive ecological and sociocultural benefits ( ''medium confidence'' ). However, this measure can be sometimes maladaptive ( ''low evidence, medium agreement'' ) and can have mitigation co-benefits ( ''low evidence, high agreement'' ) (Figure 4.29). Furthermore, water- and soil management-related measures show high potential efficacy in reducing impacts in a 1.5°C world, with declining effectiveness at higher levels of warming (Figure 4.28 and Figure 4.29)

Changes in cropping patterns, the timing of sowing and harvesting, crop diversification towards cash crops and the adoption of improved crop cultivars that can better withstand hazards like floods and drought are among the most used adaptation responses by farmers. This is among the top two measures in Asia and Africa (Figure 4.27). Extra income allows households to re-invest in improved agricultural techniques and improved cultivars ( [[#Taboada--2017|Taboada et al., 2017]] ; [[#Khanal--2018b|Khanal et al., 2018b]] ). Beneficial outcomes are documented in terms of increases in incomes and yields and water-related outcomes ( ''medium confidence'' , from ''robust evidence, but medium agreement'' ), but benefits to vulnerable communities are not always apparent on the whole (Figure FAQ4.4.1). Changes in cropping patterns and systems are also among those adaptation options assessed for their potential to reduce future climate impacts, though effectiveness is shown to be limited ( [[#Brouziyne--2018|Brouziyne et al., 2018]] ; [[#Paymard--2018|Paymard et al., 2018]] ). Assessments of the future effectiveness of crop rotation systems for adaptation show a continued reduction in required irrigation water use, though studies of effectiveness beyond 2°C global mean temperature increase are not available ( [[#Kothari--2019|Kothari et al., 2019]] ; [[#Yang--2019b|Yang et al., 2019b]] ) (Figure 4.28 and Figure 4.29).

Conservation agriculture and climate-smart agriculture (includes improved cultivars and agronomic practices) have proven to increase soil carbon, yields and technical efficiency ( [[#Penot--2018|Penot et al., 2018]] ; [[#Salat--2018|Salat and Swallow, 2018]] ; [[#Ho--2019|Ho and Shimada, 2019]] ; [[#Makate--2019|Makate and Makate, 2019]] ; [[#Okunlola--2019|Okunlola et al., 2019]] ). Some water-related measures in conservation agriculture include allowing for shading and soil moisture retention, with the co-benefit of reducing pest attacks ( [[#Thierfelder--2015|Thierfelder et al., 2015]] ; [[#Raghavendra--2018|Raghavendra and Suresh, 2018]] ; [[#Islam--2019a|Islam et al., 2019a]] ). Especially for traditional food grains in small-holder agriculture, improved practices such as modern varieties or integrated nutrient management can play an important role in making production more resilient to climate stress ( [[#Handschuch--2016|Handschuch and Wollni, 2016]] ). This measure is also among the top four most frequent adaptation measures in all continents except Australia and North America (Figure 4.27). In addition, this measure is shown to have positive economic benefits ( ''high confidence'' ) and also benefits on other parameters ( ''medium confidence'' ) (Figure FAQ4.4.1). Such approaches are also among those most frequently assessed for their effectiveness in addressing future climate change, but show limited effectiveness across warming levels (Figure 4.28 and Figure 4.29).

The use of non-conventional water sources, that is, desalinated and treated waste water, is emerging as an important component of increasing water availability for agriculture ( [[#DeNicola--2015|DeNicola et al., 2015]] ; [[#Martínez-Alvarez--2018b|Martínez-Alvarez et al., 2018b]] ; [[#Morote--2019|Morote et al., 2019]] ). While desalination has a high potential in alleviating agricultural water stress in arid coastal regions, proper management and water quality standards for desalinated irrigation water are essential to ensure continued or increased crop productivity. In addition to the energy intensity ( [[#4.7.6|Section 4.7.6]] ), risks of desalinated water include lower mineral content, higher salinity, crop toxicity and soil sodicity ( [[#Martínez-Alvarez--2018b|Martínez-Alvarez et al., 2018b]] ). Similarly, waste-water reuse can be an important contribution to buffer against the increasing variability of water resources. However, waste-water guidelines that ensure the adequate treatment to reduce adverse health and environmental outcomes due to pathogens or other chemical and organic contaminants will be essential ( [[#Angelakis--2015|Angelakis and Snyder, 2015]] ; [[#Dickin--2016|Dickin et al., 2016]] ) (Box 4.5; 4.6.4).

IKLK are crucial determinants of adaptation in agriculture for many communities globally. Indigenous Peoples have intimate knowledge about their surrounding environment and are attentive observers of climate changes. As a result, they are often best placed to enact successful adaptation measures, including shifting to different crops, changing cropping times or returning to traditional varieties ( [[#Mugambiwa--2018|Mugambiwa, 2018]] ; [[#Kamara--2019|Kamara et al., 2019]] ; [[#Nelson--2019|Nelson et al., 2019]] ) ( [[#4.8.4|Section 4.8.4]] ).

Migration and livelihood diversification is often an adaptation response to water-related hazards and involves securing income sources away from agriculture, including off-farm employment and temporary or permanent migration, and these are particularly important in Asia and Africa (Figure 4.27). Income and remittances are sometimes re-invested, for instance, for crop diversification ( [[#Rodriguez-Solorzano--2014|Rodriguez-Solorzano, 2014]] ; [[#Musah-Surugu--2018|Musah-Surugu et al., 2018]] ; [[#Mashizha--2019|Mashizha, 2019]] ). While there is extensive documentation on the benefits of migration, the quality of studies is such that links between migration and subsequent benefits are not clear, making our conclusion of benefits from this measure as having ''medium confidence'' . On the other hand, there is more rigorous evidence on the maladaptive nature of migration as an adaptation measure (Figure FAQ4.4.1). However, adverse climatic conditions, especially droughts, have been found to reduce international migration, as resources are unavailable to consider this option ( [[#Nawrotzki--2017|Nawrotzki and Bakhtsiyarava, 2017]] ), resulting in limits to adaptation ( [[#Ayeb-Karlsson--2016|Ayeb-Karlsson et al., 2016]] ; [[#Brottem--2018|Brottem and Brooks, 2018]] ; [[#Ferdous--2019|Ferdous et al., 2019]] ). In addition, it is difficult to model this option in future climate adaptation models.

Policies, institutions and capacity building are important adaptation measures in agriculture and often have beneficial outcomes, but the quality of studies precludes a high degree of certainty about those impacts (Figure FAQ4.4.1). Access to credits, subsidies or insurance builds an important portfolio of reducing reliance on agricultural income alone ( [[#Rahut--2017|Rahut and Ali, 2017]] ; [[#Wossen--2018|Wossen et al., 2018]] ). Training and capacity building are essential tools to ensure effective adaptation in agriculture, increasing food security ( [[#Chesterman--2019|Chesterman et al., 2019]] ; [[#Makate--2019|Makate and Makate, 2019]] ). Through better understanding, the implementation of available responses reduces exposure to climate impacts. In addition, public regulations, including water policies and allocations and incentive instruments, and availability of appropriate finance play an essential role in shaping and enabling (Sections 4.8.5, 4.8.6, 4.8.7), but also limiting ( [[#4.8.2|Section 4.8.2]] ), water-related adaptation for agriculture (see also Chapter 17).

Water-stressed regions already rely on importing agricultural resources, thus importing water embedded in these commodities ( [[#D’Odorico--2014|D’Odorico et al., 2014]] ). Virtual water trade will continue to play a role in reducing water-related food insecurity (Cross-Chapter Box INTERREG in Chapter 16) ( [[#Pastor--2014|Pastor et al., 2014]] ; [[#Graham--2020b|Graham et al., 2020b]] ).

While an increasing body of literature documents water-related adaptation in the agricultural sector, both in reducing current climate impacts and addressing future climate risk, knowledge gaps remain about assessing the effectiveness of such measures to reduce impacts and risks. Additional considerations on co-benefits of trade-offs for overall sustainable development are not always sufficiently considered in the available literature.

In sum, water-related adaptation in the agricultural sector is widely documented, with irrigation, agricultural water management, crop diversification and improved agronomic practices among the most common adaptation measures adopted ( ''high confidence'' ). However, the projected future effectiveness of available water-related adaptation for agriculture decreases with increasing warming ( ''medium evidence, high agreement'' ).

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'''Box 4.2 | Observed Risks, Projected Impacts and Adaptation Responses to Water Security in Small Island States'''
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AR5 and SR1.5 recognised the exceptional vulnerability of islands, especially concerning water security and potential limits to adaptation that may be reached due to freshwater resources ( [[#Klein--2014|Klein et al., 2014]] ; [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ; [[#Roy--2018|Roy et al., 2018]] ).

Small islands are already regularly experiencing droughts and freshwater shortages ( ''high confidence'' ) ( [[#Holding--2016|Holding et al., 2016]] ; [[#Pearce--2018|Pearce et al., 2018]] ; [[#Gheuens--2019|Gheuens et al., 2019]] ; [[#MacDonald--2020|MacDonald et al., 2020]] ). Freshwater supply systems vary from household or small community systems such as rainwater harvesting systems and private wells to large public water supply systems using surface, groundwater and, in some cases, desalinated water ( [[#Alsumaiei--2018b|Alsumaiei and Bailey, 2018b]] ; [[#Falkland--2020|Falkland and White, 2020]] ). In many cases, communities rely on more than one water source, including a strong reliance on rainwater and groundwater ( [[#Elliott--2017|Elliott et al., 2017]] ; [[#MacDonald--2020|MacDonald et al., 2020]] ). Groundwater resources in freshwater lenses (FWLs) are essential in providing access to freshwater resources, especially during droughts when the collected rainwater is insufficient ( [[#Barkey--2017|Barkey and Bailey, 2017]] ; [[#Bailey--2018|Bailey et al., 2018]] ), leading to greater risks of water-borne diseases, with significant effects on nutrition ( [[#Elliott--2017|Elliott et al., 2017]] ; [[#Savage--2020|Savage et al., 2020]] ), and improper sanitation poses additional risks to the limited groundwater resources ( [[#MacDonald--2017|MacDonald et al., 2017]] ). Drought events have also severely affected FWL recharge ( [[#Barkey--2017|Barkey and Bailey, 2017]] ), with extraction rates further threatening available groundwater volumes ( [[#Post--2018|Post et al., 2018]] ). In conjunction with sea level rise, this poses serious risks to groundwater salinisation ( [[#Alsumaiei--2018b|Alsumaiei and Bailey, 2018b]] ; [[#Storlazzi--2018|Storlazzi et al., 2018]] ; [[#Deng--2019|Deng and Bailey, 2019]] ). In addition, FWLs are threatened by climate change due to changes in rainfall patterns, extended droughts and wash-over events caused by storm surges and sea level rise ( ''high confidence'' ) (see Chapter 15) ( [[#Chui--2015|Chui and Terry, 2015]] ; [[#Alsumaiei--2018a|Alsumaiei and Bailey, 2018a]] ; [[#Alsumaiei--2018b|Alsumaiei and Bailey, 2018b]] ; [[#Post--2018|Post et al., 2018]] ; [[#Storlazzi--2018|Storlazzi et al., 2018]] ; [[#Deng--2019|Deng and Bailey, 2019]] ). After small-scale wash over events, the FWLs have been shown to recover to pre-wash over salinity levels within a month ( [[#Oberle--2017|Oberle et al., 2017]] ).

Due to wash-over events exacerbated by sea level rise and lens thinning due to pumping, recovery time for FWLs is projected to take substantially longer ( [[#Oberle--2017|Oberle et al., 2017]] ; [[#Alsumaiei--2018a|Alsumaiei and Bailey, 2018a]] ; [[#Storlazzi--2018|Storlazzi et al., 2018]] ). Projections indicate that atolls may be unable to provide domestic freshwater resources due to the lack of potable groundwater by 2030 (RCP8.5+ ice-sheet collapse), 2040 (RCP8.5) or the 2060s (RCP4.5) ( [[#Storlazzi--2018|Storlazzi et al., 2018]] ). Projections of future freshwater availability in small islands further underline these substantial risks to island water security ( [[#Karnauskas--2016|Karnauskas et al., 2016]] ; [[#Karnauskas--2018|Karnauskas et al., 2018]] ). Population growth, changes in rainfall patterns and agricultural demand are projected to increase water stress in small islands ( [[#Gohar--2019|Gohar et al., 2019]] ; [[#Townsend--2020|Townsend et al., 2020]] ). While some islands are projected to experience an increase in rainfall patterns, this may refer to shorter intense rainfall events, thereby increasing the risk of flooding during the wet season, while not decreasing their risk of droughts during dry periods ( [[#Aladenola--2016|Aladenola et al., 2016]] ; [[#Gheuens--2019|Gheuens et al., 2019]] ). In addition, projected shifts in the timing of the rainfall season might pose an additional risk for water supply systems ( [[#Townsend--2020|Townsend et al., 2020]] ).

Observed adaptation during drought events includes community water sharing ( [[#Bailey--2018|Bailey et al., 2018]] ; [[#Pearce--2018|Pearce et al., 2018]] ) as well as using alternative water resources such as water purchased from private companies ( [[#Aladenola--2016|Aladenola et al., 2016]] ), desalination units ( [[#Cashman--2019|Cashman and Yawson, 2019]] ; [[#MacDonald--2020|MacDonald et al., 2020]] ) or accessing deeper or new groundwater resources ( [[#Pearce--2018|Pearce et al., 2018]] ). Rainwater harvesting to adapt the water supply system in the Kingston Basin in Jamaica was able to significantly alleviate water stress, for example. Still, it would not fill the total supply gap caused by climate change ( [[#Townsend--2020|Townsend et al., 2020]] ). Likewise, groundwater sustainability with increasing climate change in Barbados cannot be ensured without aquifer protection, leading to higher optimised food prices if no additional adaptation measures are implemented ( [[#Gohar--2019|Gohar et al., 2019]] ). The potential of using multiple water sources is rarely assessed in future water supply projections in small islands ( [[#Elliott--2017|Elliott et al., 2017]] ). In the Republic of Marshall Islands, more than half of all interviewed households have already had to migrate once due to a water shortage ( [[#MacDonald--2020|MacDonald et al., 2020]] ). In Cariacou, Grenada, increases in migration rates have been observed following drought events ( [[#Cashman--2019|Cashman and Yawson, 2019]] ). with long-term cross border and internal migration shown to be having significant impacts on well-being, community-cohesion, livelihoods and people-land relationships ( [[#Yates--2021|Yates et al., 2021]] ).

In sum, small islands are already regularly experiencing droughts and freshwater shortages ( ''high confidence'' ). For atoll islands, freshwater availability may be severely limited as early as 2030 ( ''low confidence'' ). The effects of temperature increase, changing rainfall patterns, sea level rise and population pressure combined with limited options available for water-related adaptation leave small islands partially water-insecure currently, with increasing risks in the near-term and at warming above 1.5°C ( ''high confidence'' ).

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