Editing IPCC:AR6/WGII/Chapter-2 (section)

=== 2.6.3 Ecosystem-Based Adaptation ===

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A study published in 2020 found that, out of 162 intended nationally determined contributions (covering 189 countries) submitted to the United Nations Framework Convention on Climate Change (UNFCCC), as commitments to action under the Paris Agreement, 109 indicated ‘ecosystem-orientated visions’ for adaptation, but only 23 used the term ‘ecosystem-based adaptation’ ( [[#Seddon--2020b|Seddon et al., 2020b]] ).

EbA includes a range of different approaches. Examples include restoring coastal and river systems to reduce flood risk and improve water quality, and the creation of natural areas within urban areas to reduce temperatures through shading and evaporative cooling. EbA is closely linked with a variety of other concepts such as ecosystem services, natural capital and disaster risk reduction (DRR). EbA was becoming a well-recognised concept at the time of AR5 but implementation was still at an early stage in many cases. Since then, pilot studies have been assessed and EbA projects have been initiated around the world. The evidence base continues to grow (Table 2.7), and this has led to increasing confidence in approaches which have been shown to work leading to further expansion in some countries (Table 2.7). However, this is not uniform and there is relatively little synthesis across disciplines and regions ( [[#Seddon--2020a|Seddon et al., 2020a]] ). [[#Chausson--2020|Chausson et al. (2020)]] used a systematic mapping methodology to characterise 386 published studies. They found that interventions in natural or semi-natural ecosystems ameliorated adverse climate change impacts in 66% of cases, with fewer trade-offs than for more artificial systems such as plantation forest. However, the evidence base has substantial gaps. Most of the evidence has been collected in the Global North, and there is a lack of robust, site-specific investigations into the effectiveness of interventions compared to alternatives and more holistic appraisals that account for broader social and ecological outcomes.

Restoring coasts, rivers and wetlands to reduce flood risk have probably seen the largest investment in EbA and it is becoming an increasingly accepted approach in some places (e.g., case studies in Sections 2.6.5.2, 2.6.5.7), although significant social, economic and technical barriers remain ( [[#Wells--2020|Wells et al., 2020]] ; [[#Bark--2021|Bark et al., 2021]] ; [[#Hagedoorn--2021|Hagedoorn et al., 2021]] ). Natural flood management (NFM) encompasses a wide range of techniques in river systems and at the coast and has been used in varied locations around the world. In tropical and subtropical areas, the restoration of mangroves to reduce the risk of coastal flooding is a widely advocated, evidence-based approach (e.g., ( [[#Høye--2013|Høye et al., 2013]] ; [[#Sierra-Correa--2015|Sierra-Correa and Kintz, 2015]] ; [[#Powell--2019|Powell et al., 2019]] )). In temperate regions, salt marsh is a similarly important habitat ( [[#Spalding--2014|Spalding et al., 2014]] ). Both provide buffering against SLR and storm surges. Managed realignment of the coast, by creating new habitats, can lead to a loss of terrestrial and freshwater ecosystems, but it can protect them and the services they provide by reducing the risks of catastrophic failure from hard-engineered sea defences.

'''Table 2.7 |''' Examples of key EbA measures with assessments of confidence. Note only adaptation-related services are shown; many measures also provide a range of other benefits to people. All also provide benefits for biodiversity.

{| class="wikitable"
|-
! '''EbA measures'''

! '''Confidence assessment'''

! '''Ecosystem services for climate change adaptation'''

! '''Climate change impact addressed'''

! '''Social benefits from adaptation'''

! '''Relevant ecosystems and contexts'''

! '''Selected references'''

|-
| '''''Natural flood risk management in river systems: restoring natural river courses (removing canalisation), restoring and protecting wetlands and riparian vegetation'''''

| ''medium evidence,''

''medium agreement''

| Flood regulation; sediment retention; water storage; water purification

| Increased rainfall intensity

| Reduction of flood damage

Increased water security (quality and supply)

| Multiple

| ( [[#Iacob--2014|Iacob et al., 2014]] ; [[#Meli--2014|Meli et al., 2014]] ; [[#Dadson--2017|Dadson et al., 2017]] ; [[#Rowiński--2018|Rowiński et al., 2018]] ; [[#Burgess-Gamble--2021|Burgess-Gamble et al., 2021]] )

|-
| '''''Shade rivers and streams by restoration of riparian vegetation or trees.'''''

| ''medium evidence,''

''high agreement''

| Provision of fish stocks

| Warmer water temperatures

| Food security;

income benefits

| Multiple

| ( [[#Broadmeadow--2011|Broadmeadow et al., 2011]] ; [[#Isaak--2015|Isaak et al., 2015]] ; [[#Williams--2015b|Williams et al., 2015b]] ; [[#Thomas--2016|Thomas et al., 2016]] )

|-
| '''''Managed realignment of coastlines; re-establishing and protecting coastal habitats including mangroves, saltmarshes, coral reefs and oyster reefs'''''

| ''robust evidence,''

''high agreement''

| Coastal storm and flood protection;

coastal erosion control;

prevention of intrusion of salt water

| SLR;

increasing storm energy

| Protection of life, property and livelihoods;

water security

| Coastal

| ( [[#Høye--2013|Høye et al., 2013]] ; [[#Spalding--2014|Spalding et al., 2014]] ; [[#Narayan--2016|Narayan et al., 2016]] ; [[#Morris--2018|Morris et al., 2018]] ; [[#Chowdhury--2019|Chowdhury et al., 2019]] ; [[#Powell--2019|Powell et al., 2019]] )

|-
| '''''Agro-forestry and other agro-ecological/conservation practices on agricultural land'''''

| ''medium evidence,''

''medium agreement''

| Local climate regulation; soil conservation; soil nutrient regulation; water conservation; pest control; food provisioning

| High temperature or changing temperature regimes;

changing precipitation regimes

| Food security;

income benefits

| Multiple

| ( [[#Vignola--2015|Vignola et al., 2015]] ; [[#Torralba--2016|Torralba et al., 2016]] ; [[#Paul--2017|Paul et al., 2017]] ; [[#Blaser--2018|Blaser et al., 2018]] ; [[#Nesper--2019|Nesper et al., 2019]] ; [[#Verburg--2019|Verburg et al., 2019]] ; [[#Aguilera--2020|Aguilera et al., 2020]] ; [[#Tamburini--2020|Tamburini et al., 2020]] )

|-
| '''''Restore and maintain urban and peri-urban green space: trees, parks, local nature reserves, created wetlands'''''

| ''robust evidence,''

''high agreement''

| Local climate regulation;

flood regulation;

water purification;

water storage;

erosion control

| Higher temperatures and heat waves;

increased or reduced rainfall intensity

| Cooler micro-climate;

reduced flood damage;

water security

| Urban areas

| ( [[#Norton--2015|Norton et al., 2015]] ; [[#Liquete--2016|Liquete et al., 2016]] ; [[#Liu--2016|Liu, 2016]] ; [[#Bowler--2017|Bowler et al., 2017]] ; [[#Aram--2019|Aram et al., 2019]] ; [[#Stefanakis--2019|Stefanakis, 2019]] ; [[#Ziter--2019|Ziter et al., 2019]] )

|-
| '''''Ecological restoration for reducing fire risk by restoring natural vegetation and herbivory and reinstating natural fire regimes'''''

| ''medium evidence,''

''high agreement''

| Regulation of wildfires

| Mega-fires from increases in drought and heat

| Reduce deaths and infrastructure damage from fires

| Fire-adapted ecosystems

| ( [[#Waldram--2008|Waldram et al., 2008]] ; [[#Stephens--2010|Stephens et al., 2010]] ; [[#van%20Mantgem--2016|van Mantgem et al., 2016]] ; [[#Boisramé--2017|Boisramé et al., 2017]] ; [[#Johnson--2018|Johnson et al., 2018]] ; [[#Parisien--2020a|Parisien et al., 2020a]] ; [[#Parisien--2020b|Parisien et al., 2020b]] ; [[#Stephens--2020|Stephens et al., 2020]] )

|-
| '''''Invasive non-native aquatic plant control to improve water security'''''

| ''robust evidence,''

''high agreement''

| Water provision

| Increasing droughts

| Water security

| Water-scarce regions prone to an increase in droughts

| ( [[#van%20Wilgen--2016|van Wilgen and Wannenburgh, 2016]] )

|-
| '''''Woody plant control (of encroaching biomass) in open grassy ecosystems to restore and maintain grassy vegetation (see 2.4.3.5)'''''

| ''medium evidence,''

''medium agreement''

| Fodder biomass production

| Elevated CO 2 and increased rainfall promoting tree growth

| Income through bush clearing, fuelwood supplies, restore grazing

| Savanna and grasslands

| ( [[#Haussmann--2016|Haussmann et al., 2016]] )

|-
| '''''Rangeland rehabilitation and management e.g. introducing livestock enclosures, appropriate grazing management, reintroducing native grassland species'''''

| ''medium evidence,''

''medium agreement''

| Fodder biomass production; soil erosion control; soil formation; nutrient cycling; water retention

| Changing precipitation and temperature regimes including prolonged dry seasons and increased drought frequency

| Food security Water security, income benefits

| Rangelands

| ( [[#Descheemaeker--2010|Descheemaeker et al., 2010]] ; [[#Wairore--2016|Wairore et al., 2016]] ; [[#Kimiti--2017|Kimiti et al., 2017]] )

|-
| '''''Sustainable forestry of biodiverse managed forests, maintaining forest cover and protecting soils'''''

| ''medium evidence,''

''medium agreement''

| Timber production

| Increased frequency and severity of storms;

higher temperatures;

changing precipitation regimes (more intensive wet and dry periods);

increased incidents of wildfire, pest and disease outbreaks

| Livelihood and income benefits

| Boreal, temperate, subtropical, tropical forests

| ( [[#Gyenge--2011|Gyenge et al., 2011]] ; [[#Barsoum--2016|Barsoum et al., 2016]] ; [[#Jactel--2017|Jactel et al., 2017]] ; [[#Cabon--2018|Cabon et al., 2018]] )

|-
| '''''Watershed reforestation and conservation for hydrological services'''''

| ''medium evidence,''

''medium agreement''

| Flood control; erosion control; water provisioning; water purification

| Changing precipitation regimes

| Food security; Water security; Flood Protection

| Boreal, temperate, subtropical, tropical forests

| ( [[#Filoso--2017|Filoso et al., 2017]] ; [[#Bonnesoeur--2019|Bonnesoeur et al., 2019]] )

|-
| '''''Multi-functional forest management and conservation to provide climate-resilient sources of food and livelihoods and protect water sources'''''

| ''medium evidence,''

''medium agreement''

| Timber and non-timber forest production; fuel wood production; water provisioning; water purification

| Multiple

| Food security; Water security; income benefits

| Boreal, temperate, subtropical, tropical forests

| ( [[#Lunga--2016|Lunga and Musarurwa, 2016]] ; [[#Strauch--2016|Strauch et al., 2016]] ; [[#Adhikari--2018|Adhikari et al., 2018]] )

|-
| '''''Slope re-vegetation for landslide prevention and erosion control'''''

| ''robust evidence,''

''high agreement''

| Soil retention; slope stabilisation

| Increased rain frequency

| Reduced landslide damage; prevention of loss of life

| Montane and other steep-sloped regions

| ( [[#Fox--2011a|Fox et al., 2011a]] ; [[#Krautzer--2011|Krautzer et al., 2011]] ; [[#Osano--2013|Osano et al., 2013]] ; [[#Bedelian--2017|Bedelian and Ogutu, 2017]] ; [[#Getzner--2017|Getzner et al., 2017]] ; [[#de%20Jesús%20Arce-Mojica--2019|de Jesús Arce-Mojica et al., 2019]] )

|}

In river systems ( [[#Iacob--2014|Iacob et al., 2014]] ), management of both the catchments and the channel itself is important: restoring natural meanders in canalised watercourses and allowing the build-up of woody debris can slow flows rates; restoring upstream wetlands or creating them in urban and peri-urban situations can store water during flood events if they are in the right place in a catchment ( [[#Acreman--2013|Acreman and Holden, 2013]] ; [[#Ameli--2019|Ameli and Creed, 2019]] ; [[#Wu--2020|Wu et al., 2020]] ). There is less data on the potential for NFM in tropical compared to temperate catchments. However, ( [[#Ogden--2013|Ogden et al., 2013]] ) showed that flooding was reduced from a secondary forested catchment area compared to those which were pasture or a mosaic of forest, pasture and subsistence agriculture. EbA approaches to reduce flooding can be applied within urban areas as well as in rural catchments, as in Durban, South Africa ( [[#2.6.5.7|Section 2.6.5.7]] ), but effectiveness will depend on EbA being implemented at a sufficient scale and in the right locations ( [[#Hobbie--2020|Hobbie and Grimm, 2020]] ; [[#Costa--2021|Costa et al., 2021]] ). This may, in turn, provide protection to downstream urban communities.

Protecting and restoring natural river systems and natural vegetation cover within catchments as well as integrating agro-ecological techniques into agricultural systems can also help to maintain and manage water supplies for human use, under climate change, including during periods of drought, by storing water in catchments and improving water quality ( [[#Taffarello--2018|Taffarello et al., 2018]] ; [[#Agol--2021|Agol et al., 2021]] ; [[#Khaniya--2021|Khaniya et al., 2021]] ). [[#Lara--2021|Lara et al. (2021)]] showed that replacing a non-native ''Eucalyptus'' plantation in Chile with native forest caused base flow to increase by 28–87% during the restoration period compared to pre-treatment, and found that it remained during periods with low summer precipitation.

EbA can operate on a range of different scales, from local to catchment to region. On the local scale, there is a variety of circumstances in which microclimates can be managed and local temperatures lowered by the presence of vegetation (Table 2.7), and these EbA techniques are now being used more widely. In both urban and agricultural situations, shade trees are a traditional technique which can be applied to contemporary climate change adaptation. As reported in [[#2.6.2|Section 2.6.2]] above, shading of watercourses can lower temperatures, which can allow species to survive locally; as well as supporting diversity, it can help to maintain important fisheries, including those of salmonid fish ( [[#O’Briain--2020|O’Briain et al., 2020]] ). Within cities, green spaces, including parks, local nature reserves and green roofs and walls can also provide cooling as a result of evapotranspiration ( [[#Bowler--2010a|Bowler et al., 2010a]] ; [[#Aram--2019|Aram et al., 2019]] ; [[#Hobbie--2020|Hobbie and Grimm, 2020]] ), although this may be reduced in drought conditions.

Wildfire is an increasing risk for people as well as to ecosystems in many parts of the world. As discussed in [[#2.4.4.2|Section 2.4.4.2]] , this is the result not just of climate change but also past management practices, including fire suppression. Better fire management including reinstating more natural fire regimes can reduce risks.

EbA is usually a place-specific approach and a number of studies have documented how attempts to implement it without an understanding of local circumstances and the full engagement of local communities have been unsuccessful ( [[#Nalau--2018|Nalau et al., 2018]] ). Since AR5, a number of studies have considered the factors that are important for environment adaptation programmes and projects ( [[#UNFCCC--2015|UNFCCC, 2015]] ; [[#Nalau--2018|Nalau et al., 2018]] ; [[#Duncan--2020|Duncan et al., 2020]] ; [[#EPA%20Network%20and%20ENCA--2020|EPA Network and ENCA, 2020]] ; [[#Townsend--2020|Townsend et al., 2020]] ). Considering these sources, others described above and the case studies presented in [[#2.6.5|Section 2.6.5]] , a number of requirements for effective implementation of EbA can be identified, including the following:

* Targeting of the right EbA measure in the right location
* Decision-making at the appropriate level of governance with participation from all affected communities
* Integration of IKLK and capacity into decision-making and the management of projects
* Involvement of government and non-government stakeholders
* Full integration of EbA with other policy areas including agriculture, water resources and protection of natural resources
* Protection and, if possible, improvement of incomes of local people
* Effective institutional support to manage finances and the implementation of projects and programmes
* Time—many EbA interventions take time to establish, for example, for trees to grow and wetlands to recover
* Monitoring of intended outcomes and other impacts and the communication of results

Whilst it is essential to develop place-specific EbA measures with the full engagement of local communities, it is worth noting that new opportunities may emerge that would not have been possible in the past. As the climate changes, novel ecosystems may emerge (with no present day analogue) which have the potential to provide different adaptation benefits, and societies may be more willing to adopt transformative approaches ( [[#Colloff--2017|Colloff et al., 2017]] ; [[#Lavorel--2020|Lavorel et al., 2020]] ).

Increasingly, it is essential to integrate adaptation and the protection of biodiversity with land-based initiatives to mitigate climate change; this is discussed in more detail in Cross-Chapter Box NATURAL in this chapter. The new IUCN standard ( [[#IUCN--2020|IUCN, 2020]] ) offers a basis for assessing whether actions are true NbS and take into account the wider factors necessary for success.

Whilst policy interest is growing and there is an increasing deployment of EbA, there is still a long way to go in delivering its full potential ( [[#Huq--2015|Huq and Stubbings, 2015]] ) and significant institutional and cultural barriers remain ( [[#Huq--2017|Huq et al., 2017]] ; [[#Nalau--2018|Nalau et al., 2018]] ). Nevertheless, it is increasingly clear that EbA can offer a portfolio of effective measures to reduce the risks for people of climate change at the same time as benefitting biodiversity ( ''robust evidence'' , ''high agreement'' ), providing that such measures are deployed with careful planning in a way that is appropriate for local ecological and societal contexts ( ''robust evidence'' , ''high agreement'' ). This chapter has identified risks to species, communities, ecosystems and ecosystem services from climate change, all of which increase with each increment of Global Warming Level (2.5.1, 2.5.2, 2.5.3, 2.5.4). There is therefore a risk to Ecosystem-based Adaptation measures in some circumstances and this risk increases progressively above 1.5°C of warming.

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