Editing IPCC:AR6/WGIII/Chapter-8 (section)

=== 8.4.2 Spatial Planning, Urban Form, and Infrastructure ===

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Urban form is the resultant pattern and spatial layout of land use, transportation networks, and urban design elements, including the physical urban extent, configuration of streets and building orientation, and the spatial figuration within and throughout cities and towns ( [[#Lynch--1981|Lynch 1981]] ; [[#Handy--1996|Handy 1996]] ). Infrastructure describes the physical structures, social and ecological systems, and corresponding institutional arrangements that provide services and enable urban activity ( [[#Dawson--2018|Dawson et al. 2018]] ; [[#Chester--2019|Chester 2019]] ) and comprises services and built-up structures that support urban functioning, including transportation infrastructure, water and wastewater systems, solid waste systems, telecommunications, and power generation and distribution (Seto et al. 2014).

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==== 8.4.2.1 Urban Form ====

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The AR5 concluded that infrastructure and four dimensions of urban form are especially important for driving urban energy use: density, land-use mix, connectivity, and accessibility. Specifically, low-carbon cities have the following characteristics: (i) co-located medium to high densities of housing, jobs, and commerce; (ii) high mix of land uses; (iii) high connectivity of streets; and (iv) high levels of accessibility, distinguished by relatively low travel distances and travel times that are enabled by multiple modes of transportation. Urban areas with these features tend to have smaller dwelling units, smaller parcel sizes, walking opportunities, high density of intersections, and are highly accessible to shopping. For brevity, we will refer to these characteristics collectively as ‘compact and walkable urban form’ (Figure 8.16). Compact and walkable urban form has many co-benefits, including mental and physical health, lower resource demand, and saving land for AFOLU. In contrast, dispersed and auto-centric urban form is correlated with higher GHG emissions, and characterised by separated land uses, low population and job densities, large block size, and low intersection density.

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'''Figure 8.16: Urban form and implications for GHG emissions.''' Compact and walkable urban form is strongly correlated with low GHG emissions and characterised by co-located medium to high densities of housing and jobs, high street density, small block size, and mixed land use (Seto et al. 2014). Higher population densities at places of origin (e.g., home) and destination (e.g., employment, shopping) concentrate demand and are necessary for achieving the Avoid-Shift-Improve (ASI) approach for sustainable mobility (Chapters 5 and 10). Dispersed and auto-centric urban form is strongly correlated with high GHG emissions, and characterised by separated land uses, especially of housing and jobs, low street density, large block sizes, and low urban densities. Separated and low densities of employment, retail, and housing increase average travel distances for both work and leisure, and make active transport and modal shift a challenge. Since cities are systems, urban form has interacting implications across energy, buildings, transport, land use, and individual behaviour. Compact and walkable urban form enables effective mitigation while dispersed and auto-centric urban form locks-in higher levels of energy use. The colours represent different land uses and indicate varying levels of co-location and mobility options.

Since AR5, a range of studies have been published on the relationships between urban spatial structures, urban form, and GHG emissions. Multiple lines of evidence reaffirm the key findings from AR5, especially regarding the mitigation benefits associated with reducing vehicle miles or kilometres travelled (VMT/VKT) through spatial planning. There are important cascading effects not only for transport but also other key sectors and consumption patterns, such as in buildings, households, and energy. However, these benefits can be attained only when the existing spatial structure of an urban area does not limit locational and mobility options, thereby avoiding carbon lock-in through the interaction of infrastructure and the resulting socio-behavioural aspects.

Modifying the layout of emerging urbanisation to be more compact, walkable, and co-located can reduce future urban energy use by 20–25% in 2050 while providing a corresponding mitigation potential of 23–26% ( [[#Creutzig--2015|Creutzig et al. 2015]] , 2016b; [[#Sethi--2020|Sethi et al. 2020]] ), forming the basis for other urban mitigation options. Cross-Chapter Box 7 in [[IPCC:Wg3:Chapter:Chapter-10|Chapter 10]] provides perspectives on simultaneously reducing urban transport emissions, avoiding infrastructure lock-in, and providing accessible services. The systemic nature of compact urban form and integrated spatial planning influences ‘Avoid-Shift-Improve’ (ASI, see Glossary) options across several sectors simultaneously, including for mobility and shelter (for an in-depth discussion on the integration of service provision solutions within the ASI framework, see [[IPCC:Wg3:Chapter:Chapter-5#5.3|Section 5.3]] ).

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==== 8.4.2.2 Co-located Housing and Jobs, Mixed Land Use, and High Street Connectivity ====

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Integrated spatial planning, co-location of higher residential and job densities, and systemic approaches are widely identified with development that is characterised by the 5Ds of transit-oriented development (TOD) based on density, diversity (mixed land uses), design (street connectivity), destination accessibility, and distance to transit. Spatial strategies that integrate the 5Ds are shown to reduce VMT/VKT, and thereby transport-related GHG emissions through energy savings. The effect of urban form and built environment strategies on VMT per capita varies by a number of factors ( [[#Ewing--2010|Ewing and Cervero 2010]] ; [[#Stevens--2017|Stevens 2017]] ; [[#Blanco--2018|Blanco and Wikstrom 2018]] ). Density and destination accessibility have the highest elasticities, followed by design ( [[#Stevens--2017|Stevens 2017]] ). Population-weighted densities for 121 metropolitan areas have further found that the concentration of population and jobs along mass transit corridors decreases VMT/VKT significantly when compared to more dispersed metropolitan areas. In this sample, elasticity rates were twice as high for dense metropolitan areas located along mass transit lines ( [[#Lee--2020|Lee and Lee 2020]] ).

Meta-analyses of the reduction in VMT and the resulting GHG emissions consider the existing and still dominant use of emitting transportation technology, transportation fleets, and urban form characteristics. Varied historical legacies of transportation and the built environment, which can be utilised to develop more sustainable cities ( [[#Newman--2016|Newman et al. 2016]] , 2017), are often not taken into account directly. Metropolitan policies and spatial planning, as evident in Copenhagen’s Finger Plan, as well as strategic spatial planning in Stockholm and Seoul, have been major tools to restructure urban regions and energy patterns ( [[#Sung--2017|Sung and Choi 2017]] ). Road prices and congestion charges can provide the conditions for urban inhabitants to shift mobility demands and reduce vehicle use ( [[IPCC:Wg3:Chapter:Chapter-5#5.6.2|Section 5.6.2]] ). Surprisingly, even cities with higher population densities and a greater range of land uses can show declines in these important attributes, which can lead to emissions increases, such as found in a study of 323 East and South East Asian cities ( [[#Chen--2020c|Chen et al. 2020c]] ). Conversely, the annual CO 2 emissions reduction of passenger cars in compact versus dispersed urban form scenarios can include at least a 10% reduction by 2030 ( [[#Matsuhashi--2016|Matsuhashi and Ariga 2016]] ). When combined with advances in transport technology, this share increases to 64–70% in 2050 based on compact urban form scenarios for 1727 municipalities ( [[#Kii--2020|Kii 2020]] ).

As a reaffirmation of AR5, population density reduces emissions per capita in the transport, building, and energy sectors ( [[#Baur--2015|Baur et al. 2015]] ; [[#Gudipudi--2016|Gudipudi et al. 2016]] ; [[#Wang--2017|Wang et al. 2017]] ; [[#Yi--2017|Yi et al. 2017]] ) (see also Sections 8.3.1 and 8.3.4 on past trends and forecasts of urban population density and land expansion). Urban compactness tends to reduce emissions per capita in the transport sector, especially for commuting ( [[#Matsuhashi--2016|Matsuhashi and Ariga 2016]] ; [[#Lee--2018|Lee and Lim 2018]] ; [[#Lee--2020|Lee and Lee 2020]] ). The relative accessibility of neighbourhoods to the rest of the region, in addition to the density of individual neighbourhoods, is important ( [[#Ewing--2018|Ewing et al. 2018]] ). Creating higher residential and employment densities, developing smaller block sizes, and increasing housing opportunities in an employment area can significantly reduce household car ownership and car driving, and increase the share of transit, walk, and bicycle commuting ( [[#Ding--2018|Ding et al. 2018]] ). In addition to population density, land-use mix, rail transit accessibility, and street design reduce emissions from transport ( [[#Dou--2016|Dou et al. 2016]] ; [[#Cao--2017|Cao and Yang 2017]] ; [[#Choi--2018|Choi 2018]] ). The impact of population density and urban compactness on emissions per capita in the household or energy sector is also associated with socioeconomic characteristics or lifestyle preferences ( [[#Baiocchi--2015|Baiocchi et al. 2015]] ; [[#Miao--2017|Miao 2017]] ). Changes in the attributes of urban form and spatial structure have influences on overall energy demand across spatial scales, particularly street, block, neighbourhood, and city scales, as well as across the building (housing) and transport (mobility) sectors ( [[#Silva--2017|Silva et al. 2017]] ). Understanding the existing trade-offs (or synergetic links) between urban form variables across major emissions source sectors, and how they impact the size of energy flows within the urban system, is key to prioritising action for energy-efficient spatial planning strategies, which are likely to vary across urban areas.

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==== 8.4.2.3 Urban Form, Growth, and Sustainable Development ====

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Spatial planning for compact urban form is a system-wide intervention ( [[#Sethi--2020|Sethi et al. 2020]] ) and has potential to be combined with sustainable development objectives while pursuing climate mitigation for urban systems ( [[#Große--2016|Große et al. 2016]] ; [[#Cheshmehzangi--2017|Cheshmehzangi and Butters 2017]] ; [[#Facchini--2017|Facchini et al. 2017]] ; [[#Lwasa--2017|Lwasa 2017]] ; [[#Stokes--2019|Stokes and Seto 2019]] ). Compact urban form can enable positive impacts on employment and green growth given that the local economy is decoupled from GHG emissions and related parameters while the concentration of people and activity can increase productivity based on both proximity and efficiency ( [[#Lee--2017|Lee and Erickson 2017]] ; [[#Salat--2017|Salat et al. 2017]] ; [[#Gao--2018|Gao and Newman 2018]] ; [[#Han--2018|Han et al. 2018]] ; [[#Li--2018|Li and Liu 2018]] ; [[#Lall--2021|Lall et al. 2021]] ).

Public acceptance can have a positive impact on integrated spatial planning especially when there is a process of co-design ( [[#Grandin--2018|Grandin et al. 2018]] ; [[#Webb--2018|Webb et al. 2018]] ). The quality of spatial planning can also increase co-benefits for health and well-being, including decisions to balance urban green areas with density ( [[#Li--2016|Li et al. 2016]] ; [[#Sorkin--2018|Sorkin 2018]] ; [[#Pierer--2019|Pierer and Creutzig 2019]] ). The distributional effects of spatial planning can depend on the policy tools that shape the influence of urban densification on affordable housing while evidence for transit-induced gentrification is found to be partial and inconclusive ( [[#Chava--2016|Chava and Newman 2016]] ; [[#Jagarnath--2018|Jagarnath and Thambiran 2018]] ; [[#Padeiro--2019|Padeiro et al. 2019]] ; [[#Debrunner--2020|Debrunner and Hartmann 2020]] ) (Sections 8.2 and 8.4.4).

Reducing GHG emissions across different urban growth typologies (Figure 8.20) depends in part on the ability to integrate opportunities for climate mitigation with co-benefits for health and well-being ( [[#Grandin--2018|Grandin et al. 2018]] ). At the same time, requirements for institutional capacity and governance for cross-sector coordination for integrated urban planning is high given the complex relations between urban mobility, buildings, energy systems, water systems, ecosystem services, other urban sectors, and climate adaptation ( [[#Große--2016|Große et al. 2016]] ; [[#Castán%20Broto--2017a|Castán Broto 2017a]] ; [[#Endo--2017|Endo et al. 2017]] ; [[#Geneletti--2017|Geneletti et al. 2017]] ). The capacity for implementing land-use zoning and regulations in a way that is consistent with supporting spatial planning for compact urban form is not equal across urban areas and depends on different contexts as well as institutional capacities ( [[#Bakır--2018|Bakır et al. 2018]] ; [[#Deng--2018|Deng et al. 2018]] ; [[#Shen--2019|Shen et al. 2019]] ).

Currently, integrating spatial planning, urban form, and infrastructure in urban mitigation strategies remains limited in mainstream practices, including in urban areas targeting an emissions reduction of 36–80% in the next decades ( [[#Asarpota--2020|Asarpota and Nadin 2020]] ). Capacity building for integrated spatial planning for urban mitigation includes increasing collaboration among city departments and with civil society to develop robust mitigation strategies, bringing together civil engineers, architects, urban designers, public policy and spatial planners, and enhancing the education of urban professionals ( [[#Asarpota--2020|Asarpota and Nadin 2020]] ) ( [[#8.5|Section 8.5]] ).

Spatial planning for compact urban form is a prerequisite for efficient urban infrastructure, including district heating and/or cooling networks ( [[#Swilling--2018|Swilling et al. 2018]] ; [[#Möller--2019|Möller et al. 2019]] ; [[#Persson--2019|Persson et al. 2019]] ; [[#UNEP%20IRP--2020|UNEP IRP 2020]] ). District heating and cooling networks benefit from urban design parameters, including density, block area, and elongation that represent the influence of urban density on energy density ( [[#Fonseca--2015|Fonseca and Schlueter 2015]] ; [[#Shi--2020|Shi et al. 2020]] ). Heat- demand density is a function of both population density and heat demand per capita and can be equally present in urban areas with high population density or high heat demand per capita ( [[#Möller--2019|Möller et al. 2019]] ; [[#Persson--2019|Persson et al. 2019]] ). Low-temperature networks that utilise waste heat or renewable energy can provide an option to avoid carbon lock-in to fossil fuels while layout and eco-design principles can further optimise such networks ( [[#Gang--2016|Gang et al. 2016]] ; [[#Buffa--2019|Buffa et al. 2019]] ; [[#Dominković--2019|Dominković and Krajačić 2019]] ). Replacing gas-based heating and cooling with electrified district heating and cooling networks, for instance, provides 65% emissions reductions also involving carbon-aware scheduling for grid power ( [[#De%20Chalendar--2019|De Chalendar et al. 2019]] ). The environmental and ecological benefits increase through the interaction of urban energy and spatial planning ( [[#Tuomisto--2015|Tuomisto et al. 2015]] ; [[#Bartolozzi--2017|Bartolozzi et al. 2017]] ; [[#Dénarié--2018|Dénarié et al. 2018]] ; [[#Zhai--2020|Zhai et al. 2020]] ). These interactions include support for demand-side flexibility, spatial planning using geographic information systems, and access to renewable and urban waste heat sources ( [[#Möller--2018|Möller et al. 2018]] ; [[#REN21--2020|REN21 2020]] ; [[#Sorknæs--2020|Sorknæs et al. 2020]] ; [[#Dorotić--2019|Dorotić et al. 2019]] ) (see Table 8.SM.2 for other references).

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