Editing IPCC:AR6/WGII/Chapter-6 (section)

=== 6.3.4 Adaptation Through Nature-Based Solutions ===

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Well-functioning ecosystems can play a significant role in buffering cities, settlements and infrastructure from climate hazards at multiple scales ( ''robust evidence'' , ''high agreement'' ). Nature-based solutions (NBS) are actions to protect, sustainably manage and restore natural or modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits (Cohen-Shacham et al., 2016). Widely recognised as low-regret measures for disaster risk reduction and climate change adaptation, green and blue infrastructure investments and natural area conservation in cities can provide NBS across scales to reduce temperature shocks and provide natural flood defences among other adaptation and resilience benefits (McPhearson et al., 2018; Andersson et al., 2019; Frantzeskaki et al., 2019). Blue infrastructure, for example, provides ecological and hydrological functions (e.g., evaporation, transpiration, drainage, infiltration, detention) critical to sustainable urban water management (Iojă et al., 2021). Public parks, urban forests, street trees and green roofs, as well as lakes, ponds and streams are widely documented for providing local cooling, grass and riparian buffers, forested watersheds can enhance flood and drought protection for cities and settlements, and mangrove stands and wetlands in coastal areas can reduce storm surges. Despite increasing knowledge about NBS (here encompassing literature on ecosystem services for climate change adaptation and resilience, ecosystem-based adaptation, and benefits of green and blue infrastructure for adaptation), recent studies indicate that nature-based approaches to adaptation and resilience are still under-recognised and under-invested in urban planning and development (Matthews, Lo and Byrne, 2015; [[#Geneletti--2016|Geneletti and Zardo, 2016]] ; Frantzeskaki et al., 2019), despite the potential scale of benefits, for example, a recent study covering 70 cities in Latin America calculated that 96 million people would benefit from improving main watersheds with green infrastructure (Tellman et al., 2018).

Grey infrastructure often damages or eliminates biophysical processes (e.g., through soil sealing, stream burial or altered hydrology) necessary to sustain ecosystems, habitats and livelihoods, where urban ecological infrastructure (Childers et al., 2019) can be more flexible and cost effective for providing flood risk reduction and other benefits (Palmer et al., 2015). Hybrid approaches are emerging that integrate ecological and grey (engineered) infrastructure in adaptation planning and hazard protection (Grimm et al., 2016; [[#Depietri--2017|Depietri and McPhearson, 2017]] ). Explicit policy uptake by city authorities is increasing (Hansen et al., 2015; Hölscher et al., 2019), such as in New York where in 2010 the city committed to a hybrid infrastructure plan for storm water management, investing USD 5.3 billion over 20 years, of which USD 2.4 billion was targeted for green infrastructure investments ( [[#NYC--2010|NYC, 2010]] ). A subset of services from urban ecosystems are being increasingly invested in as NBS for climate adaptation pathways (Keeler et al., 2019; Kabisch et al., 2016) and included as regulatory drivers through flood management, hazard mitigation and air pollution regulations that encourage or enforce the implementation of green infrastructure practices (Davis et al., 2020).

Development and climate mitigation co-benefits of NBS is an additional reason that NBS are being increasingly taken up by cities, including for improving health and livelihoods, particularly for poor, marginalised groups (Poulsen et al., 2015; Poulsen, Neff and Winch, 2017; Maughan, Laycock Pedersen and Pitt, 2018; [[#Simon-Rojo--2019|Simon-Rojo, 2019]] ; [[#Cederlöf--2016|Cederlöf, 2016]] ). Co-benefits include a wide range of social and environmental benefits (Brink et al., 2016; Alves et al., 2019) for human physical and mental health (Kabisch, van den Bosch and Lafortezza, 2017; Sarkar, Webster and Gallacher, 2018; Engemann et al., 2019; Rojas-Rueda et al., 2019), climate mitigation (De la Sota et al., 2019) and as habitat for local biodiversity ( [[#Ziter--2016|Ziter, 2016]] ; Knapp, Schmauck and Zehnsdorf, 2019). At the same time, concerns about the unintended consequences of investing in green infrastructure for NBS, such as how it may contribute to gentrification (Turkelboom et al., 2018; Anguelovski et al., 2018; Haase et al., 2017), create more public use, increase water demand (Nouri, Borujeni and Hoekstra, 2019) or contribute to criminal activity ( [[#Cilliers--2015|Cilliers and Cilliers, 2015]] ) underlines the challenges of investing in adaptation in complex urban systems (see [[#6.2.6|Section 6.2.6]] ). Additionally, more place-based analyses of the efficacy of NBS for reducing climate impacts across varying urban contexts and future climate scenarios are needed to better understand the cost effectiveness of investing in NBS to provide disaster risk reduction and deliver critical co-benefits for human well-being. Cooperation between scientists, decision-makers and Indigenous knowledge-holders can supplement current efforts and ensure that investments in NBS do not negatively impact indigenous communities (Ban et al., 2018; Seddon et al., 2021; Townsend, Moola and Craig, 2020).

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==== 6.3.4.1 Temperature Regulation ====

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Nature-based strategies, including street trees, green roofs, green walls and other urban vegetation, can reduce heat and extreme heat by cooling private and public spaces ( ''robust evidence'' , ''high agreement'' ). Shading and evapotranspiration are the primary mechanisms for vegetation-induced urban cooling (Coutts et al., 2016). Shading reduces mean radiant temperature, which is the dominant influence on outdoor human thermal comfort under warm, sunny conditions (Thorsson et al., 2014; Viguié et al., 2020). Outdoor green space and parks may also slightly reduce indoor heat hazard (Viguié et al., 2020). Apart from lowering temperature, NBS may also contribute to lower energy costs by reducing extra demand for conventional sources of cooling (e.g., air conditioning) (Viguié et al., 2020; Foustalieraki et al., 2017), especially during peak demand periods. Homes with shade trees that are located in cities where air conditioning systems are common can save over 30% of residential peak cooling demand (Zardo et al., 2017; Wang et al., 2015). Green roofs have been shown to significantly lower surface temperatures on buildings (Bevilacqua et al., 2017) and modelling suggests that green roofs, if employed widely throughout urban areas, have the potential to impact the regional heat profile of cities (Bevilacqua et al., 2017; Rosenzweig, Gaffin and Parshall, 2006). Community or allotment gardens, backyard greening and other types of low vegetation, as well as lakes, ponds, rivers and streams, can also provide local cooling benefits to nearby residents (Gunawardena, Wells and Kershaw, 2017; Larondelle et al., 2014; [[#Santamouris--2020|Santamouris, 2020]] ).

Urban climate models show that increased vegetation cover results in reducing both mean air temperatures and extreme temperatures during heatwaves (Heaviside, Cai and Vardoulakis, 2015; [[#Ferreira--2019|Ferreira and Duarte, 2019]] ; [[#Schubert--2013|Schubert and Grossman-Clarke, 2013]] ). Greater density and more canopy coverage relative to other built and paved surfaces increases shade provision and evapotranspiration (Hamstead et al., 2016; Grilo et al., 2020; Herath, Halwatura and Jayasinghe, 2018; Knight et al., 2021). However, local cooling by vegetation depends on regional climate context, geographic setting of the city, urban form, the density and placement of the trees, in addition to a variety of other ecological, technical, and social factors, such as local stewardship (Salmond et al., 2016). Green spaces less than 0.5–2.0 ha may have negligible cooling effects at regional scales, but impacts of shading can have microscale cooling benefits (Gunawardena, Wells and Kershaw, 2017; Zardo et al., 2017). Vegetation impacts on day versus night-time cooling varies (Imran et al., 2019) as does cooling potential in temperate versus tropical climates. The supply of cooler air from surrounding peri-urban and rural areas can impact cooling in the urban core suggesting that regional adaptation planning for NBS is important to maintain or extend ventilation paths from the urban fringe into the city centre (Schau-Noppel, Kossmann and Buchholz, 2020).

To maximize the adaptation benefits of NBS for regulating urban heat, it can be helpful to prioritise tree planting and other urban greening investments in areas where heat vulnerability and risk are the highest, especially communities that lack urban tree canopy or accessibility to parks to cool off during hot days or heatwaves (Ziter et al., 2019). Planting trees closely together or in partly permeable vegetated barriers along streets can improve local cooling benefits. Additionally, choosing tree species with leaves that have the greatest leaf area index or the largest leaves can improve cooling performance, as those trees have the greatest shading and evapotranspiration benefits that, in turn, provide the greatest cooling effects (Keeler et al., 2019). Drought-resistant trees, often native trees, are ideal to avoid high watering costs, though dry or water scarce areas may limit adoption of urban vegetation as an NBS strategy (Coutts et al., 2013). Native trees and permaculture can provide additional benefits for local biodiversity as shown in study in Melbourne, Australia which found that increasing vegetation from 10% to 30% increased occupancy of bats, birds, bees, beetles and bugs by up to 130% (Threlfall et al., 2017), with particularly high impact on native species.. Additionally, planting fruit or nut trees can provide co-benefits for local food production, and yet choice of species and placement is important to consider with respect to local cultural needs and norms ( [[#Adegun--2018|Adegun, 2018]] ; [[#Adegun--2017|Adegun, 2017]] ).

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==== 6.3.4.2 Air Quality Regulation ====

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NBS in cities can help regulate air quality by absorbing air pollutants ( ''medium evidence'' , ''medium agreement'' ). For example, planting trees or vegetated barriers along streets or in urban forests can reduce particulate matter, the ambient air pollutant with the largest global health burden ( [[#Janhäll--2015|Janhäll, 2015]] ; Tiwary, Reff and Colls, 2008; Matos et al., 2019; McDonald et al., 2016). However, findings show that trees can also positively affect ground-level ozone (Calfapietra et al., 2013; Kroeger et al., 2014), airborne pollen concentrations ( [[#Willis--2017|Willis and Petrokofsky, 2017]] ) and indirectly affect air quality through reduced emissions from energy production offset by shade provision (Keeler et al., 2019). Certain tree species however can also be detrimental to urban ozone formation by emitting significant amounts of reactive biogenic volatile organic compounds (VOCs). Decreasing urban emissions of VOCs is an increasingly important ozone mitigation strategy in urban areas (Fitzky et al., 2019).

Trees can also have negative effects by increasing pedestrian exposure to pollution if they are introduced in heavily travelled street canyons where air pollutants can be trapped (Vos et al., 2013; [[#Gromke--2015|Gromke and Blocken, 2015]] ). To maximise the adaptation benefits of NBS for improving air quality, planners and managers can target tree selection for species with low VOC emissions, low allergen emissions and high pollutant deposition potential (Keeler et al., 2019), and combine with low pollution transportation policies. Studies suggest sensitive planting of roadside tree canopies can have positive effects on air pollutants (Beckett, Freer Smith and Taylor, 2000; Yang, Chang and Yan, 2015). For example, [[#Xue--2021|Xue et al. (2021)]] found that the PM2.5 reduction between 2013 and 2017 in China was associated with a saving of approximately USD 111 billion yr -1 nationally. Tree planting near schools, nursing homes and hospitals can ensure that benefits provided by trees are delivered to the local populations that stand to benefit the most from improved air quality, but species need to be adapted to regional climate to provide benefits over time ( [[#Donovan--2017|Donovan, 2017]] ; Nowak et al., 2018).

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==== 6.3.4.3 Stormwater Regulation and Sanitation ====

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Urban parks and open spaces, forests, wetlands, green roofs and engineered stormwater treatment devices help manage stormwater and wastewater by reducing the volume of stormwater runoff, reducing surface flooding, and reducing contamination of runoff by pollutants ( ''robust evidence'' , ''high agreement'' ). Engineered devices include bioswales, rain gardens, and detention and retention ponds, and are becoming common and standard approaches to mitigate the negative effects of impervious surfaces on stormwater quality and surface flooding in cities ( [[#Zhou--2014|Zhou, 2014]] ; McPhillips et al., 2020). Allotment gardens, street trees, green roofs and urban forests may also help reduce runoff and provide a stormwater retention service (Pennino, McDonald and Jaffe, 2016; Berland et al., 2017; Gittleman et al., 2017). Modelling and empirical studies show that NBS at small spatial scales lead to improvements in water quality and reduction of peak flows (Moore et al., 2016; Keeler et al., 2019; Webber et al., 2020). Peak flow reductions are greatest for small rain events. For example, D-Ville et al. (2018) observed a 30–70% reduction in peak flow for the 1-in-30 year storm, but performance reduces for more intense rainfall or if saturated (Garofalo et al., 2016). Employing NBS to reduce flooding on roads can be an important adaptation mechanism for reducing the impact of flooding events on traffic flows (Pregnolato et al., 2016).

During periods with intense precipitation, low-lying urban parks and open space, engineered devices and wetlands can play an important role in reducing stormwater runoff volumes by providing places for water to be stored and infiltrate during heavy storms (Moore et al., 2016). However, the magnitude of the runoff reduction service will depend on the total area of green infrastructure, vegetation type and its position on the landscape. There is less evidence of the effectiveness of NBS at larger temporal and spatial scales (Pregnolato et al., 2017; Jefferson et al., 2017). The performance of NBS depends on the degree to which their extent and spatial configuration in the city are optimised to capture runoff ( [[#Fry--2017|Fry and Maxwell, 2017]] ). Investing in a diversity of NBS types may be important to maximise stormwater management and flood regulation, as different types of engineered NBS have different strengths and weaknesses.

Overall, NBS are attractive adaptation options for stormwater management and to reduce impacts of pluvial and fluvial flooding in cities (Rosenzweig et al., 2018a) compared, and in combination, with grey infrastructure. Cities with combined sewer infrastructure are ''likely'' to see benefits from NBS due to reductions in stormwater quantity and reduced sewage overflows. Cities where a large proportion of residents lack access to piped infrastructure and drink surface water may see large benefits, especially to human health, from NBS investments (Keeler et al., 2019). Where future large-scale upgrades or installation of grey infrastructure will be necessary, new and growing cities may have more opportunity to realise large net benefits from investments in NBS. Older cities, and new, rapidly urbanising areas that lack large-scale water infrastructure may see the greatest benefits from enhanced NBS, relative to cities where heavy investments infrastructure upgrades have already been made. Cities facing climate changes that include more frequent or extreme precipitation may also see large water quality benefits from investment in NBS (Keeler et al., 2019). Overall, there is increasing evidence that NBS for addressing stormwater is cost effective (Bixler et al., 2020; Kozak et al., 2020; Mguni, Herslund and Jensen, 2016), especially in cities facing a need to update current infrastructures.

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==== 6.3.4.4 Coastal Flood Protection ====

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Coastal ecosystems including coral and oyster reefs, coastal forests including mangroves and other tree species, salt marshes and other types of wetland habitat, seagrass, dunes and barrier islands can reduce impacts of coastal flooding and storms ( ''robust evidence'' , ''high agreement'' ) (Zhao, Roberts and Ludy, 2014; [[#Boutwell--2016|Boutwell and Westra, 2016]] ; Narayan et al., 2017; Yang, Kerger and Nepf, 2015; Bridges et al., 2015; [[#World%20Bank--2016|World Bank, 2016]] ) (see also Section CCP2 Cities and Settlements by the Sea). Recent literature highlights the value of nature-based approaches for coastal protection in terms of avoided damages and human well-being (Narayan et al., 2017; Silva et al., 2016a). NBS can protect coasts from flooding through reducing the wave energy by drag friction, reducing wave overtopping by eliminating vertical barriers, and absorbing floodwaters in soil (Arkema, Scyphers and Shepard, 2017; Dasgupta et al., 2019; Zhu et al., 2020). For example, coastal and marine vegetation and reefs can dissipate wave energy, attenuate wave heights and nearshore currents, decrease the extent of wave run-up on beaches, and trap sediments (Ferrario et al., 2014; Bridges et al., 2015). These effects result in lower water levels and reduce shoreline erosion, which in turn has potential to save lives and prevent expensive property damages (Narayan et al., 2017).

Researchers, practitioners and policy-makers are increasingly calling for the use of nature-based approaches to protect urban shorelines from coastal hazards ( [[#Cunniff--2015|Cunniff and Schwartz, 2015]] ; Bilkovic et al., 2017). The expectation is that coastal ecosystems can help stabilise shorelines, protect communities against storm surge and from tidal-influenced flooding, while providing other co-benefits for people and ecosystems. However, vegetation along protected coastlines with higher frequency, lower intensity coastal hazards ( [[#National%20Research%20Council--2014|National Research Council, 2014]] ) may be more effective for stabilising shorelines and reducing risk to coastal communities and properties, and benefits will depend on local hydrology of the coastal region. [[#Narayan--2017|Narayan et al. (2017)]] estimate that coastal wetlands alone reduced direct flood damages by USD 625 million during Hurricane Sandy in the USA in 2012. Similarly, researchers found that villages with wider mangroves between them and the coast experienced significantly fewer deaths than villages with narrow or no mangroves during a 1999 cyclone in India ( [[#World%20Bank--2016|World Bank, 2016]] ). Recently, Arkema et al. (2017) noted that the number of people, poor families, elderly and total value of residential property most exposed to hazards along the entire coast of the USA can be reduced by half if existing coastal habitats remain fully intact.

Coastal habitats also have limitations in their ability to protect coasts from extreme events. Some studies suggest reduced effectiveness of vegetation and reefs for coastal protection from large storm waves and surge (Möller et al., 2014; Guannel et al., 2016) and there is active debate in the literature about the ability of ecosystems to mitigate the impact of tsunamis (Gillis et al., 2017). Further research is needed to understand and quantify coastal protection services provided by these hybrid green-grey solutions, especially in urban areas (Bilkovic et al., 2017). Additionally, in some coastlines, water may be too deep or waves too high for some species such as mangroves to grow, thrive and provided needed NBS.

Maximising the adaptation benefits of NBS for improving coastal flood protection research requires that cities seek to restore and conserve the vegetation and reef types that are appropriate for the exposure setting and in sufficient abundance to be effective. In particular, planners and managers can use vegetation in protected bays as alternatives to hard infrastructure for shoreline stabilisation. However, the influence of ecosystems on flooding and erosion is variable and depends on a suite of social, ecological and infrastructural factors that vary within and among urban areas (Narayan et al., 2017; Ruckelshaus et al., 2016; Bridges et al., 2015). Additionally, long-term planning to restore or ensure resilience of individual species and ecosystems that may themselves be damaged or destroyed during extreme events is needed in order for urban green and blue infrastructure to continue providing NBS over the longer term.

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==== 6.3.4.5 Riverine Flood Impact Reduction ====

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NBS reduce both the volume of floodwater and the impact of floods ( ''medium evidence'' , ''medium agreement'' ). NBS reduce the volume of runoff by increasing infiltration and water storage (Shuster et al., 2005; Salvadore, Bronders and Batelaan, 2015), and affect the production and impact of flood waters through reducing river energy and flow speed through physical blockage, stabilising riverbanks during flood events, creating space for floodwaters to expand and combating land subsidence (Palmer, Filoso and Fanelli, 2014; Ahilan et al., 2018). Installing NBS to increase infiltration on low slopes and high-permeability soils can reduce the impacts of potential increases in urban flooding driven by climate change, especially for small- to medium-scale flood events (lower than 20% mean annual flood) (Moftakhari et al., 2018).

Source reduction strategies include creating permeable areas such as parks and open spaces, as well as engineered devices such as raingardens, bioswales and retention ponds that help retain stormwater runoff from impervious areas. River restoration can reduce flood peak flow and provide space for floodwaters to expand. Planting and maintaining vegetation along riverbanks, often in the form of parks or river restoration, maintains structural integrity during flood events. Wetland construction and improved connectivity to floodplains also reduces flood peaks. Efforts to restore floodplains are important to create space for floodwaters and reduce exposure by moving people out of the hazard zone. Floodplain restoration also provides access to the river that has multiple benefits including recreation, access to water for domestic use and other cultural ecosystem services. A key adaptation strategy is to reduce streambank erosion (a result of high peak flow) using riparian vegetation to stabilise riverbanks during flood events.

Cities manage flood risk using different types of adaptation and regulatory mechanisms ( [[#Naturally%20Resilient%20Communities--2017|Naturally Resilient Communities, 2017]] ). Built flood-control infrastructure, such as levees and stream channelisation, reduces the demand for nature-based flood impact reduction. Cities facing flood risk that do not currently have extensive grey flood-mitigation infrastructure may find NBS to be an appealing, lower cost solution (Keeler et al., 2019). In cities where flood-control grey infrastructure already exists, there is less demand for NBS of flood protection, but NBS may provide important back up, especially in a changing climate that may increase flood hazards ( [[#City%20of%20Los%20Angeles--2017|City of Los Angeles, 2017]] ; Elmqvist et al., 2019). Overall, city and basin-wide NBS for riverine flood impact reduction can reduce the generation of new hazards by making space for water which can reduce the potential for a false sense of security provided by traditional flood management approaches (Ruangpan et al., 2020; Turkelboom et al., 2021).

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==== 6.3.4.6 Water Provisioning and Management ====

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The role of NBS has been increasingly recognised for improving urban water management, emphasising it’s contribution for climate-adapted development and sustainable urbanisation ( ''robust evidence'' , ''high agreement'' ) ( [[#Wong--2009|Wong and Brown, 2009]] ). NBS that protect or restore the natural infiltration capacity of a watershed can increase the water supply service to various extents, improving drought protection and providing resilient water supply (Drosou et al., 2019; [[#Krauze--2019|Krauze and Wagner, 2019]] ), although different forms of NBS (e.g., street trees, parks and open space, community gardens, and engineered devices such as rain gardens, bioswales or retention ponds) contribute in different ways to increasing stormwater infiltration. Additional sources of water may be available to replace the water supplied by NBS, such as rainwater harvesting, inter-basin transfers or desalination plants. Reliance on naturally sourced, locally available surface water and groundwater is more energy efficient and economical than desalination or water reuse for potable use (Boelee et al., 2017), while rainwater harvesting is even more economical. Increasing the amount of green space in urban areas can secure and regulate water supplies, improving water security ( [[#Liu--2018|Liu and Jensen, 2018]] ; Bichai and Cabrera Flamini, 2018). However, [[#Bhaskar--2016|Bhaskar et al. (2016)]] reviewed the effect of urbanisation and NBS on baseflow and suggest that the confounded effects of infiltration and evapotranspiration losses, combined with the subsurface infrastructure (sewer systems) and geology, makes it difficult to predict the magnitude of baseflow enhancement resulting from the implementation of NBS in cities.

To maximise the adaptation benefits of NBS for urban water supply research suggests that managers and planners consider NBS as alternatives to traditional stormwater management techniques, where possible, since these solutions can promote groundwater recharge. As green infrastructure is increasingly being used for stormwater absorption in cities (McPhillips et al., 2020), rain gardens, wetlands, or engineered infiltration ponds and bioswales are the NBS most likely to promote recharge, reduce evapotranspiration and contribute to water provisioning.

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==== 6.3.4.7 Food Production and Security ====

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Urban agriculture can serve as a NBS for food security ( ''medium evidence'' , ''medium agreement'' ) across a range of urban contexts ( [[#Lwasa--2015|Lwasa and Dubbeling, 2015]] ; Nogeire-McRae et al., 2018; Pourias, Aubry and Duchemin, 2016) by contributing to food provisioning as well as providing co-benefits including for recreation, place making and mental health (Petrovic et al., 2019; Soga, Gaston and Yamaura, 2017; Goldstein et al., 2016b).

Urban agriculture among poorer communities in lower income areas is already an important source of food supply for those communities, contributing to food security and health (Orsini et al., 2013). However, potential for expanding open air urban food production may be practically constrained by land availability ( [[#Badami--2015|Badami and Ramankutty, 2015]] ; Martellozzo et al., 2014). This is particularly true in some lower-income countries where rapid urbanisation is occurring, which compounds existing food insecurity (Satterthwaite, McGranahan and Tacoli, 2010; Vermeiren et al., 2013). Land availability and suitability for gardens can be further constrained by land use history, including past industrial uses that can contaminate soils with pollutants such as lead.

At the same time, investments in vertical agriculture continue to expand, such as in Singapore where private investment in food production is occurring in high rise buildings (Wong, Wood and Paturi, 2020). Not all cities can benefit similarly from vertical agriculture since higher heating costs to produce vegetables indoors during northern winters consumes considerable amounts of energy and may generate fossil fuel emissions depending on the energy source (Goldstein et al., 2016a; Mohareb et al., 2017). Some regions can benefit from more traditional outdoor urban farming, such as in South and Southeast Asia, which can support multiple growing cycles per year for some crops, particularly in tropical areas where irrigation is available. Light availability, soil health and water availability will impact food production in urban areas. For example, a study conducted in Vancouver, Canada, demonstrated that light attenuation from buildings and trees can reduce both crop yield and water demand for crop growth (Johnson et al., 2015).

Climate change may have important impacts on urban food production and food security. While urban agriculture may provide benefits in terms of stability of food access in low-income households in some regions of the Global South where the climate is warmer, the shorter growing seasons in colder climates will reduce the role of outdoor urban agriculture in year-round food supply and diets. Though urban agriculture constitutes a small fraction of total food consumption in some urban areas, several studies have attempted to estimate the extent to which urban agriculture could theoretically meet urban total food or vegetable demand ( [[#Badami--2015|Badami and Ramankutty, 2015]] ; [[#McClintock--2014|McClintock, 2014]] ; Hara et al., 2018). Maximising the adaptation and resilience benefits of NBS for food production and security suggests the need to embrace the multi-functionality of urban agriculture, rather than viewing it as solely concerning food production (Barthel, Parker and Ernstson, 2015).

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