Editing IPCC:AR6/SR15/Chapter-4 (section)

=== 4.3.3 Urban and Infrastructure System Transitions ===

<div id="section-4-3-3-block-1"></div>

There will be approximately 70 million additional urban residents every year through to the middle part of this century (UN DESA, 2014) <sup>[[#fn:r289|289]]</sup> . The majority of these new urban citizens will reside in small and medium-sized cities in low- and middle-income countries (Cross-Chapter Box 13 in Chapter 5). The combination of urbanization and economic and infrastructure development could account for an additional 226 GtCO <sub>2</sub> by 2050 (Bai et al. 2018). However, urban systems can harness the mega-trends of urbanization, digitalization, financialization and growing sub-national commitment to smart cities, green cities, resilient cities, sustainable cities and adaptive cities, for the type of transformative change required by 1.5°C-consistent pathways (SDSN, 2013; Parag and Sovacool, 2016; Roberts, 2016; Wachsmuth et al., 2016; Revi, 2017; Solecki et al., 2018) <sup>[[#fn:r290|290]]</sup> . There is a growing number of urban climate responses driven by cost-effectiveness, development, work creation and inclusivity considerations (Solecki et al., 2013; Ahern et al., 2014; Floater et al., 2014; Revi et al., 2014a; Villarroel Walker et al., 2014; Kennedy et al., 2015; Rodríguez, 2015; McGranahan et al., 2016; Dodman et al., 2017a; Newman et al., 2017; UN-Habitat, 2017; Westphal et al., 2017) <sup>[[#fn:r291|291]]</sup> .

In addition, low-carbon cities could reduce the need to deploy carbon dioxide removal (CDR) and solar radiation modification (SRM) (Fink, 2013; Thomson and Newman, 2016) <sup>[[#fn:r292|292]]</sup> .

Cities are also places in which the risks associated with warming of 1.5°C, such as heat stress, terrestrial and coastal flooding, new disease vectors, air pollution and water scarcity, will coalesce (see Chapter 3, Section 3.3) (Dodman et al., 2017a; Satterthwaite and Bartlett, 2017) <sup>[[#fn:r293|293]]</sup> . Unless adaptation and mitigation efforts are designed around the need to decarbonize urban societies in the developed world and provide low-carbon solutions to the needs of growing urban populations in developing countries, they will struggle to deliver the pace or scale of change required by 1.5°C-consistent pathways (Hallegatte et al., 2013; Villarroel Walker et al., 2014; Roberts, 2016; Solecki et al., 2018) <sup>[[#fn:r294|294]]</sup> . The pace and scale of urban climate responses can be enhanced by attention to social equity (including gender equity), urban ecology (Brown and McGranahan, 2016; Wachsmuth et al., 2016; Ziervogel et al., 2016a) <sup>[[#fn:r295|295]]</sup> and participation in sub-national networks for climate action (Cole, 2015; Jordan et al., 2015) <sup>[[#fn:r296|296]]</sup> .

The long-lived urban transport, water and energy systems that will be constructed in the next three decades to support urban populations in developing countries and to retrofit cities in developed countries will have to be different to those built in Europe and North America in the 20th century, if they are to support the required transitions (Freire et al., 2014; Cartwright, 2015; McPhearson et al., 2016; Roberts, 2016; Lwasa, 2017) <sup>[[#fn:r297|297]]</sup> . Recent literature identifies energy, infrastructure, appliances, urban planning, transport and adaptation options as capable of facilitating systemic change. It is these aspects of the urban system that are discussed below and from which options in Section 4.5 are selected.

<div id="section-4-3-3-1"></div>

<span id="urban-energy-systems"></span>
==== 4.3.3.1 Urban energy systems ====

<div id="section-4-3-3-1-block-1"></div>

Urban economies tend to be more energy intensive than national economies due to higher levels of per capita income, mobility and consumption (Kennedy et al., 2015; Broto, 2017; Gota et al., 2018) <sup>[[#fn:r298|298]]</sup> . However, some urban systems have begun decoupling development from the consumption of fossil fuel-powered energy through energy efficiency, renewable energy and locally managed smart grids (Dodman, 2009; Freire et al., 2014; Eyre et al., 2018; Glazebrook and Newman, 2018) <sup>[[#fn:r299|299]]</sup> .

The rapidly expanding cities of Africa and Asia, where energy poverty currently undermines adaptive capacity (Westphal et al., 2017; Satterthwaite et al., 2018) <sup>[[#fn:r300|300]]</sup> , have the opportunity to benefit from recent price changes in renewable energy technologies to enable clean energy access to citizens (SDG 7) (Cartwright, 2015; Watkins, 2015; Lwasa, 2017; Kennedy et al., 2018; Teferi and Newman, 2018) <sup>[[#fn:r301|301]]</sup> . This will require strengthened energy governance in these countries (Eberhard et al., 2017) <sup>[[#fn:r302|302]]</sup> . Where renewable energy displaces paraffin, wood fuel or charcoal feedstocks in informal urban settlements, it provides the co-benefits of improved indoor air quality, reduced fire risk and reduced deforestation, all of which can enhance adaptive capacity and strengthen demand for this energy (Newham and Conradie, 2013; Winkler, 2017; Kennedy et al., 2018; Teferi and Newman, 2018) <sup>[[#fn:r303|303]]</sup> .

<div id="section-4-3-3-2"></div>

<span id="urban-infrastructure-buildings-and-appliances"></span>
==== 4.3.3.2 Urban infrastructure, buildings and appliances ====

<div id="section-4-3-3-2-block-1"></div>

Buildings are responsible for 32% of global energy consumption (IEA, 2016c) <sup>[[#fn:r304|304]]</sup> and have a large energy saving potential with available and demonstrated technologies such as energy efficiency improvements in technical installations and in thermal insulation (Toleikyte et al., 2018) <sup>[[#fn:r305|305]]</sup> and energy sufficiency (Thomas et al., 2017) <sup>[[#fn:r306|306]]</sup> . Kuramochi et al. (2018) <sup>[[#fn:r307|307]]</sup> show that 1.5°C-consistent pathways require building emissions to be reduced by 80–90% by 2050, new construction to be fossil-free and near-zero energy by 2020, and an increased rate of energy refurbishment of existing buildings to 5% per annum in OECD (Organisation for Economic Co-operation and Development) countries (see also Section 4.2.1).

Based on the IEA-ETP (IEA, 2017g) <sup>[[#fn:r308|308]]</sup> , Chapter 2 identifies large saving potential in heating and cooling through improved building design, efficient equipment, lighting and appliances. Several examples of net zero energy in buildings are now available (Wells et al., 2018) <sup>[[#fn:r309|309]]</sup> . In existing buildings, refurbishment enables energy saving (Semprini et al., 2017; Brambilla et al., 2018; D’Agostino and Parker, 2018; Sun et al., 2018) <sup>[[#fn:r310|310]]</sup> and cost savings (Toleikyte et al., 2018; Zangheri et al., 2018) <sup>[[#fn:r311|311]]</sup> .

Reducing the energy embodied in building materials provides further energy and GHG savings (Cabeza et al., 2013; Oliver and Morecroft, 2014; Koezjakov et al., 2018) <sup>[[#fn:r312|312]]</sup> , in particular through increased use of bio-based materials (Lupíšek et al., 2015) <sup>[[#fn:r313|313]]</sup> and wood construction (Ramage et al., 2017) <sup>[[#fn:r314|314]]</sup> . The United Nations Environment Programme (UNEP3) <sup>[[#fn:3|3]]</sup> estimates that improving embodied energy, thermal performance, and direct energy use of buildings can reduce emissions by 1.9 GtCO <sub>2</sub> e yr <sup>−1</sup> (UNEP, 2017b) <sup>[[#fn:r315|315]]</sup> '','' with an additional reduction of 3 GtCO <sub>2</sub> e yr <sup>−1</sup> through energy efficient appliances and lighting (UNEP, 2017b) <sup>[[#fn:r316|316]]</sup> ''.'' Further increasing the energy efficiency of appliances and lighting, heating and cooling offers the potential for further savings (Parikh and Parikh, 2016; Garg et al., 2017) <sup>[[#fn:r317|317]]</sup> .

Smart technology, drawing on the internet of things (IoT) and building information modelling, offers opportunities to accelerate energy efficiency in buildings and cities (Moreno-Cruz and Keith, 2013; Hoy, 2016) <sup>[[#fn:r318|318]]</sup> (see also Section 4.4.4). Some cities in developing countries are drawing on these technologies to adopt ‘leapfrog’ infrastructure, buildings and appliances to pursue low-carbon development (Newman et al., 2017; Teferi and Newman, 2017) <sup>[[#fn:r319|319]]</sup> (Cross-Chapter Box 13 in Chapter 5).

<div id="section-4-3-3-3"></div>

<span id="urban-transport-and-urban-planning"></span>
==== 4.3.3.3 Urban transport and urban planning ====

<div id="section-4-3-3-3-block-1"></div>

Urban form impacts demand for energy (Sims et al., 2014) <sup>[[#fn:r320|320]]</sup> and other welfare related factors: a meta-analysis of 300 papers reported energy savings of 26 USD per person per year attributable to a 10% increase in urban population density (Ahlfeldt and Pietrostefani, 2017) <sup>[[#fn:r321|321]]</sup> . Significant reductions in car use are associated with dense, pedestrianized cities and towns and medium-density transit corridors (Newman and Kenworthy, 2015; Newman et al., 2017) <sup>[[#fn:r322|322]]</sup> relative to low-density cities in which car dependency is high (Schiller and Kenworthy, 2018) <sup>[[#fn:r323|323]]</sup> . Combined dense urban forms and new mass transit systems in Shanghai and Beijing have yielded less car use (Gao and Newman, 2018) <sup>[[#fn:r324|324]]</sup> (see Box 4.9). Compact cities also create the passenger density required to make public transport more financially viable (Rode et al., 2014; Ahlfeldt and Pietrostefani, 2017) <sup>[[#fn:r325|325]]</sup> and enable combinations of cleaner fuel feedstocks and urban smart grids, in which vehicles form part of the storage capacity (Oldenbroek et al., 2017) <sup>[[#fn:r326|326]]</sup> . Similarly, the spatial organization of urban energy influenced the trajectories of urban development in cities as diverse as Hong Kong, Bengaluru and Maputo (Broto, 2017) <sup>[[#fn:r327|327]]</sup> .

The informal settlements of middle- and low-income cities, where urban density is more typically associated with a range of water- and vector-borne health risks, may provide a notable exception to the adaptive advantages of urban density (Mitlin and Satterthwaite, 2013; Lilford et al., 2017) <sup>[[#fn:r328|328]]</sup> unless new approaches and technologies are harnessed to accelerate slum upgrading (Teferi and Newman, 2017) <sup>[[#fn:r329|329]]</sup> .

Scenarios consistent with 1.5°C depend on a roughly 15% reduction in final energy use by the transport sector by 2050 relative to 2015 (Chapter 2, Figure 2.12). In one analysis the phasing out of fossil fuel passenger vehicle sales by 2035–2050 was identified as a benchmark for aligning with 1.5°C-consistent pathways (Kuramochi et al., 2018) <sup>[[#fn:r330|330]]</sup> . Reducing emissions from transport has lagged the power sector (Sims et al., 2014; Creutzig et al., 2015a) <sup>[[#fn:r331|331]]</sup> , but evidence since AR5 suggests that cities are urbanizing and re-urbanizing in ways that coordinate transport sector adaptation and mitigation (Colenbrander et al., 2017; Newman et al., 2017; Salvo et al., 2017; Gota et al., 2018) <sup>[[#fn:r332|332]]</sup> . The global transport sector could reduce 4.7 GtCO2e yr <sup>−1</sup> (4.1–5.3) by 2030. This is significantly more than is predicted by integrated assessment models (UNEP, 2017b) <sup>[[#fn:r333|333]]</sup> . Such a transition depends on cities that enable modal shifts and avoided journeys and that provide incentives for uptake of improved fuel efficiency and changes in urban design that encourage walkable cities, non-motorized transport and shorter commuter distances (IEA, 2016a; Mittal et al., 2016; Zhang et al., 2016; Li and Loo, 2017) <sup>[[#fn:r334|334]]</sup> . In at least 4 African cities, 43 Asian cities and 54 Latin American cities, transit-oriented development (TOD), has emerged as an organizing principle for urban growth and spatial planning (Colenbrander et al., 2017; Lwasa, 2017; BRTData, 2018) <sup>[[#fn:r335|335]]</sup> . This trend is important to counter the rising demand for private cars in developing-country cities (AfDB/OECD/UNDP, 2016) <sup>[[#fn:r336|336]]</sup> . In India, TOD has been combined with localized solar PV installations and new ways of financing rail expansion (Sharma, 2018) <sup>[[#fn:r337|337]]</sup> .

Cities pursuing sustainable transport benefit from reduced air pollution, congestion and road fatalities and are able to harness the relationship between transport systems, urban form, urban energy intensity and social cohesion (Goodwin and Van Dender, 2013; Newman and Kenworthy, 2015; Wee, 2015) <sup>[[#fn:r338|338]]</sup> .

Technology and electrification trends since AR5 make carbon-efficient urban transport easier (Newman et al., 2016) <sup>[[#fn:r339|339]]</sup> , but realizing urban transport’s contribution to a 1.5°C-consistent pathways will require the type of governance that can overcome the financial, institutional, behavioural and legal barriers to change (Geels, 2014; Bakker et al., 2017) <sup>[[#fn:r340|340]]</sup> .

Adaptation to a 1.5°C world is enabled by urban design and spatial planning policies that consider extreme weather conditions and reduce displacement by climate related disasters (UNISDR, 2009; UN-Habitat, 2011; Mitlin and Satterthwaite, 2013) <sup>[[#fn:r341|341]]</sup> .

Building codes and technology standards for public lighting, including traffic lights (Beccali et al., 2015) <sup>[[#fn:r342|342]]</sup> , play a critical role in reducing carbon emissions, enhancing urban climate resilience and managing climate risk (Steenhof and Sparling, 2011; Parnell, 2015; Shapiro, 2016; Evans et al., 2017) <sup>[[#fn:r343|343]]</sup> . Building codes can support the convergence to zero emissions from buildings (Wells et al., 2018) <sup>[[#fn:r344|344]]</sup> and can be used retrofit the existing building stock for energy efficiency (Ruparathna et al., 2016) <sup>[[#fn:r345|345]]</sup> .

The application of building codes and standards for 1.5°C-consistent pathways will require improved enforcement, which can be a challenge in developing countries where inspection resources are often limited and codes are poorly tailored to local conditions (Ford et al., 2015c; Chandel et al., 2016; Eisenberg, 2016; Shapiro, 2016; Hess and Kelman, 2017; Mavhura et al., 2017) <sup>[[#fn:r346|346]]</sup> . In all countries, building codes can be undermined by industry interests and can be maladaptive if they prevent buildings or land use from evolving to reduce climate impacts (Eisenberg, 2016; Shapiro, 2016) <sup>[[#fn:r347|347]]</sup> .

The deficit in building codes and standards in middle-income and developing-country cities need not be a constraint to more energy-efficient and resilient buildings (Tait and Euston-Brown, 2017) <sup>[[#fn:r348|348]]</sup> . For example, the relatively high price that poor households pay for unreliable and at times dangerous household energy in African cities has driven the uptake of renewable energy and energy efficiency technologies in the absence of regulations or fiscal incentives (Eberhard et al., 2011, 2016; Cartwright, 2015; Watkins, 2015) <sup>[[#fn:r349|349]]</sup> . The Kuyasa Housing Project in Khayelitsha, one of Cape Town’s poorest suburbs, created significant mitigation and adaptation benefits by installing ceilings, solar water heaters and energy-efficient lightbulbs in houses independent of the formal housing or electrification programme (Winkler, 2017) <sup>[[#fn:r350|350]]</sup> .

<div id="section-4-3-3-4"></div>

<span id="electrification-of-cities-and-transport"></span>
==== 4.3.3.4 Electrification of cities and transport ====

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The electrification of urban systems, including transport, has shown global progress since AR5 (IEA, 2016a; Kennedy et al., 2018; Schiller and Kenworthy, 2018) <sup>[[#fn:r351|351]]</sup> . High growth rates are now appearing in electric vehicles (Figure 4.1), electric bikes and electric transit (IEA, 2018) <sup>[[#fn:r352|352]]</sup> , which would need to displace fossil fuel-powered passenger vehicles by 2035–2050 to remain in line with 1.5°C-consistent pathways. China’s 2017 Road Map calls for 20% of new vehicle sales to be electric. India is aiming for exclusively electric vehicles (EVs) by 2032 (NITI Aayog and RMI, 2017) <sup>[[#fn:r353|353]]</sup> . Globally, EV sales were up 42% in 2016 relative to 2015, and in the United States EV sales were up 36% over the same period (Johnson and Walker, 2016) <sup>[[#fn:r354|354]]</sup> .

<div id="section-4-3-3-4-block-2"></div>

<span id="figure-4.1"></span>
<!-- START IMG -->
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'''Figure 4.1'''

<span id="increase-of-the-global-electric-car-stock-by-country-20132017."></span>
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'''Increase of the global electric car stock by country (2013–2017).'''
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[[File:7a745c048d60a7c92d6bc6d3b4f1c107 fig-4.1-1024x588.jpg]]

The grey line is battery electric vehicles (BEV) only while the black line includes both BEV and plug-in hybrid vehicles (PHEV). Source: (IEA, 2018) <sup>[[#fn:r355|355]]</sup> . Based on IEA data from Global EV Outlook 2018 © OECD/IEA 2018, IEA Publishing.

<!-- END IMG -->
<div id="section-4-3-3-4-block-3"></div>

The extent of electric railways in and between cities has expanded since AR5 (IEA, 2016a; Mittal et al., 2016; Zhang et al., 2016; Li and Loo, 2017) <sup>[[#fn:r356|356]]</sup> . In high-income cities there is ''medium evidence'' for the decoupling of car use and wealth since AR5 (Newman, 2017) <sup>[[#fn:r357|357]]</sup> . In cities where private vehicle ownership is expected to increase, less carbon-intensive fuel sources and reduced car journeys will be necessary as well as electrification of all modes of transport (Mittal et al., 2016; van Vuuren et al., 2017) <sup>[[#fn:r358|358]]</sup> . Some recent urban data show a decoupling of urban growth and GHG emissions (Newman and Kenworthy, 2015) <sup>[[#fn:r359|359]]</sup> and that ‘peak car’ has been reached in Shanghai and Beijing (Gao and Kenworthy, 2017) <sup>[[#fn:r360|360]]</sup> and beyond (Manville et al., 2017) <sup>[[#fn:r361|361]]</sup> (also see Box 4.9).

An estimated 800 cities globally have operational bike-share schemes (E. Fishman et al., 2015) <sup>[[#fn:r362|362]]</sup> , and China had 250 million electric bicycles in 2017 (Newman et al., 2017) <sup>[[#fn:r363|363]]</sup> . Advances in information and communication technologies (ICT) offer cities the chance to reduce urban transport congestion and fuel consumption by making better use of the urban vehicle fleet through car sharing, driverless cars and coordinated public transport, especially when electrified (Wee, 2015; Glazebrook and Newman, 2018) <sup>[[#fn:r364|364]]</sup> . Advances in ‘big-data’ can assist in creating a better understanding of the connections between cities, green infrastructure, environmental services and health (Jennings et al., 2016) <sup>[[#fn:r365|365]]</sup> and improve decision-making in urban development (Lin et al., 2017) <sup>[[#fn:r366|366]]</sup> .

<div id="section-4-3-3-5"></div>

<span id="shipping-freight-and-aviation"></span>
==== 4.3.3.5 Shipping, freight and aviation ====

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International transport hubs, including airports and ports, and the associated mobility of people are major economic contributors to most large cities even while under the governance of national authorities and international legislation. Shipping, freight and aviation systems have grown rapidly, and little progress has been made since AR5 on replacing fossil fuels, though some trials are continuing (Zhang, 2016; Bouman et al., 2017; EEA, 2017) <sup>[[#fn:r367|367]]</sup> . Aviation emissions do not yet feature in IAMs (Bows-Larkin, 2015) <sup>[[#fn:r368|368]]</sup> , but could be reduced by between a third and two-thirds through energy efficiency measures and operational changes (Dahlmann et al., 2016) <sup>[[#fn:r369|369]]</sup> . On shorter intercity trips, aviation could be replaced by high-speed electric trains drawing on renewable energy (Åkerman, 2011) <sup>[[#fn:r370|370]]</sup> . Some progress has been made on the use of electricity in planes and shipping (Grewe et al., 2017) <sup>[[#fn:r371|371]]</sup> though no commercial applications have arisen. Studies indicate that biofuels are the most viable means of decarbonizing intercontinental travel, given their technical characteristics, energy content and affordability (Wise et al., 2017) <sup>[[#fn:r372|372]]</sup> . The lifecycle emissions of bio-based jet fuels and marine fuels can be considerable (Cox et al., 2014; IEA, 2017g) <sup>[[#fn:r373|373]]</sup> depending on their location (Elshout et al., 2014) <sup>[[#fn:r374|374]]</sup> , but can be reduced by feedstock and conversion technology choices (de Jong et al., 2017) <sup>[[#fn:r375|375]]</sup> .

In recent years the potential for transport to use synfuels, such as ethanol, methanol, methane, ammonia and hydrogen, created from renewable electricity and CO <sub>2</sub> , has gained momentum but has not yet demonstrated benefits on a scale consistent with 1.5°C pathways (Ezeji, 2017; Fasihi et al., 2017) <sup>[[#fn:r376|376]]</sup> . Decarbonizing the fuel used by the world’s 60,000 large ocean vessels faces governance barriers and the need for a global policy (Bows and Smith, 2012; IRENA, 2015; Rehmatulla and Smith, 2015) <sup>[[#fn:r377|377]]</sup> . Low-emission marine fuels could simultaneously address sulphur and black carbon issues in ports and around waterways and accelerate the electrification of all large ports (Bouman et al., 2017; IEA, 2017g) <sup>[[#fn:r378|378]]</sup> .

<div id="section-4-3-3-x"></div>

<span id="climate-resilient-land-use"></span>
==== 4.3.3.6 Climate-resilient land use ====

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Urban land use influences energy intensity, risk exposure and adaptive capacity (Carter et al., 2015; Araos et al., 2016a; Ewing et al., 2016; Newman et al., 2016; Broto, 2017) <sup>[[#fn:r379|379]]</sup> . Accordingly, urban land-use planning can contribute to climate mitigation and adaptation (Parnell, 2015; Francesch-Huidobro et al., 2017) <sup>[[#fn:r380|380]]</sup> and the growing number of urban climate adaptation plans provide instruments to do this (Carter et al., 2015; Dhar and Khirfan, 2017; Siders, 2017; Stults and Woodruff, 2017) <sup>[[#fn:r381|381]]</sup> . Adaptation plans can reduce exposure to urban flood risk (which, in a 1.5°C world, could double relative to 1976–2005; Alfieri et al., 2017) <sup>[[#fn:r382|382]]</sup> , heat stress (Chapter 3, Section 3.5.5.8), fire risk (Chapter 3, Section 3.4.3.4) and sea level rise (Chapter 3,

Section 3.4.5.1) (Schleussner et al., 2016) <sup>[[#fn:r383|383]]</sup> .

Cities can reduce their risk exposure by considering investment in infrastructure and buildings that are more resilient to warming of 1.5°C or beyond. Where adaptation planning and urban planning generate the type of local participation that enhances capacity to cope with risks, they can be mutually supportive processes  (Archer et al., 2014; Kettle et al., 2014; Campos et al., 2016; Chu et al., 2017; Siders, 2017; Underwood et al., 2017) <sup>[[#fn:r384|384]]</sup> . Not all adaptation plans are reported as effective (Measham et al., 2011; Hetz, 2016; Woodruff and Stults, 2016; Mahlkow and Donner, 2017) <sup>[[#fn:r385|385]]</sup> , especially in developing-country cities (Kiunsi, 2013) <sup>[[#fn:r386|386]]</sup> . In cases where adaptation planning may further marginalize poor citizens, either through limited local control over adaptation priorities or by displacing impacts onto poorer communities, successful urban risk management would need to consider factors such as justice, equity, and inclusive participation, as well as recognize the political economy of adaptation (Archer, 2016; Shi et al., 2016; Ziervogel et al., 2016a, 2017; Chu et al., 2017) <sup>[[#fn:r387|387]]</sup> .

<div id="section-4-3-3-7"></div>

<span id="green-urban-infrastructure-and-ecosystem-services"></span>
==== 4.3.3.7 Green urban infrastructure and ecosystem services ====

<div id="section-4-3-3-7-block-1"></div>

Integrating and promoting green urban infrastructure (including street trees, parks, green roofs and facades, and water features) into city planning can be difficult (Leck et al., 2015) <sup>[[#fn:r388|388]]</sup> but increases urban resilience to impacts of 1.5°C warming (Table 4.2) in ways that can be more cost-effective than conventional infrastructure (Cartwright et al., 2013; Culwick and Bobbins, 2016) <sup>[[#fn:r389|389]]</sup> .

<div id="section-4-3-3-7-block-2"></div>

<span id="table-4.2"></span>
<!-- START TABLE -->
'''Table 4.2'''

<span id="green-urban-infrastructure-and-benefits"></span>
'''Green urban infrastructure and benefits'''

<!-- TABLE -->
{| class="wikitable"
|-
! Green<br />
Infrastructure
! Adaptation<br />
Benefits
! Mitigation<br />
Benefits
! References
|-
| Urban tree planting,<br />
urban parks
| Reduced heat island effect, psychological benefits
| Less cement, reduced air-conditioning use
| Demuzere et al., 2014; Mullaney et al., 2015; Soderlund and Newman, 2015; Beaudoin and Gosselin, 2016; Green et al., 2016; Lin et al., 2017 <sup>[[#fn:r390|390]]</sup>
|-
| Permeable surfaces
| Water recharge
| Less cement in city, some bio-sequestration, less water pumping
| Liu et al., 2014; Lamond et al., 2015; Skougaard Kaspersen et al., 2015; Voskamp and Van de Ven, 2015; Costa et al., 2016; Mguni et al., 2016; Xie et al., 2017 <sup>[[#fn:r391|391]]</sup>
|-
| Forest retention, urban agricultural land
| Flood mediation, healthy lifestyles
| Reduced air pollution
| Nowak et al., 2006; Tallis et al., 2011; Elmqvist et al., 2013; Buckeridge, 2015; Culwick and Bobbins, 2016; Panagopoulos et al., 2016; Stevenson et al., 2016; R. White et al., 2017 <sup>[[#fn:r392|392]]</sup>
|-
| Wetland restoration, riparian buffer zones
| Reduced urban flooding, low-skilled local work, sense of place
| Some bio-sequestration,<br />
less energy spent on water treatment
| Cartwright et al., 2013; Elmqvist et al., 2015; Brown and McGranahan, 2016; Camps-Calvet et al., 2016; Culwick and Bobbins, 2016; McPhearson et al., 2016; Ziervogel et al., 2016b; Collas et al., 2017; F. Li et al., 2017 <sup>[[#fn:r393|393]]</sup>
|-
| Biodiverse urban habitat
| Psychological benefits, inner-city recreation
| Carbon sequestration
| Beatley, 2011; Elmqvist et al., 2015; Brown and McGranahan, 2016; Camps-Calvet et al., 2016; McPhearson et al., 2016; Collas et al., 2017; F. Li et al., 2017 <sup>[[#fn:r394|394]]</sup>
|}
<!-- END TABLE -->

<div id="section-4-3-3-7-block-3"></div>

Realizing climate benefits from urban green infrastructure sometimes requires a city-region perspective (Wachsmuth et al., 2016) <sup>[[#fn:r395|395]]</sup> . Where the urban impact on ecological systems in and beyond the city is appreciated, the potential for transformative change exists (Soderlund and Newman, 2015; Ziervogel et al., 2016a) <sup>[[#fn:r396|396]]</sup> , and a locally appropriate combination of green space, ecosystem goods and services and the built environment can increase the set of urban adaptation options (Puppim de Oliveira et al., 2013) <sup>[[#fn:r397|397]]</sup> .

Milan, Italy, a city with deliberate urban greening policies, planted 10,000 hectares of new forest and green areas over the last two decades (Sanesi et al., 2017) <sup>[[#fn:r398|398]]</sup> . The accelerated growth of urban trees, relative to rural trees, in several regions of the world is expected to decrease tree longevity (Pretzsch et al., 2017) <sup>[[#fn:r399|399]]</sup> , requiring monitoring and additional management of urban trees if their contribution to urban ecosystem-based adaptation and mitigation is to be maintained in a 1.5°C world (Buckeridge, 2015; Pretzsch et al., 2017) <sup>[[#fn:r400|400]]</sup> .

<div id="section-4-3-3-8-2"></div>

<span id="sustainable-urban-water-and-environmental-services"></span>
==== 4.3.3.8 Sustainable urban water and environmental services ====

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Urban water supply and wastewater treatment is energy intensive and currently accounts for significant GHG emissions (Nair et al., 2014) <sup>[[#fn:r401|401]]</sup> . Cities can integrate sustainable water resource management and the supply of water services in ways that support mitigation, adaptation and development through waste water recycling and storm water diversion (Xue et al., 2015; Poff et al., 2016) <sup>[[#fn:r402|402]]</sup> . Governance and finance challenges complicate balancing sustainable water supply and rising urban demand, particularly in low-income cities (Bettini et al., 2015; Deng and Zhao, 2015; Hill Clarvis and Engle, 2015; Lemos, 2015; Margerum and Robinson, 2015) <sup>[[#fn:r403|403]]</sup> .

Urban surface-sealing with impervious materials affects the volume and velocity of runoff and flooding during intense rainfall (Skougaard Kaspersen et al., 2015) <sup>[[#fn:r404|404]]</sup> , but urban design in many cities now seeks to mediate runoff, encourage groundwater recharge and enhance water quality (Liu et al., 2014; Lamond et al., 2015; Voskamp and Van de Ven, 2015; Costa et al., 2016; Mguni et al., 2016; Xie et al., 2017) <sup>[[#fn:r405|405]]</sup> . Challenges remain for managing intense rainfall events that are reported to be increasing in frequency and intensity in some locations (Ziervogel et al., 2016b) <sup>[[#fn:r406|406]]</sup> , and urban flooding is expected to increase at 1.5°C of warming (Alfieri et al., 2017) <sup>[[#fn:r407|407]]</sup> . This risk falls disproportionately on women and poor people in cities (Mitlin, 2005; Chu et al., 2016; Ziervogel et al., 2016b; Chant et al., 2017; Dodman et al., 2017a, b) <sup>[[#fn:r408|408]]</sup> .

Nexus approaches that highlight urban areas as socio-ecological systems can support policy coherence (Rasul and Sharma, 2016) <sup>[[#fn:r409|409]]</sup> and sustainable urban livelihoods (Biggs et al., 2015) <sup>[[#fn:r410|410]]</sup> . The water–energy–food (WEF) nexus is especially important to growing urban populations (Tacoli et al., 2013; Lwasa et al., 2014; Villarroel Walker et al., 2014) <sup>[[#fn:r411|411]]</sup> .

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