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

==== 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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