Editing IPCC:AR6/WGIII/Chapter-7 (section)

==== 7.3.1.2 Infrastructure Development and Urbanisation ====

<div id="h3-7-siblings" class="h3-siblings"></div>

Although built-up areas (defined as cities, towns, villages and human infrastructure) occupy a relatively small fraction of land (around 1% of global land), since 1975 urban clusters (i.e., urban centres as well as surrounding suburbs) have expanded approximately 2.5 times ( [[#UNEP--2019|UNEP 2019]] ; Chapter 8, this report). Regional differences are striking. Between 1975 and 2015, built-up areas doubled in size in Europe while urban population remained relatively constant. In Africa built-up areas grew approximately fourfold, while urban population tripled ( [[#UNEP--2019|UNEP 2019]] ). Trends indicate that rural-to-urban migration will continue and accelerate in developing countries increasing environmental pressure in spite of measures to mitigate some of the impacts (e.g., by preserving or enhancing natural systems within cities, for example, lakes or natural and urban green infrastructures ( [[#UNEP--2019|UNEP 2019]] ). If current population densities within cities remain stable, the extent of built-up areas in developed countries is expected to increase by 30% and triple in developing countries between 2000 and 2050 (Barger et al. 2018).

Urban expansion leads to landscape fragmentation and urban sprawl with effects on forest resources and land use ( [[#Ünal--2019|Ünal et al. 2019]] ) while interacting with other drives. For example, in the Brazilian Amazon, the most rapid urban growth occurs within cities that are located near rural areas that produce commodities (minerals or crops) and are connected to export corridors ( [[#Richards--2015|Richards and VanWey 2015]] ). Urbanisation, coastal development and industrialisation also play crucial roles in the significant loss of mangrove forests (Hirales-Cota 2010; [[#Richards--2016|Richards and Friess 2016]] ; [[#Rivera-Monroy--2017|Rivera-Monroy et al. 2017]] ). Among infrastructural developments, roads are one of the most consistent and most considerable factors in deforestation, particularly in tropical frontiers ( [[#Pfaff--2007|Pfaff et al. 2007]] ; [[#Rudel--2009|Rudel et al. 2009]] ; [[#Ferretti-Gallon--2014|Ferretti-Gallon and Busch 2014]] ). The development of roads may also bring subsequent impacts on further development intensity due to increasing economic activities (see Chapter 8) mostly in the tropics and subtropics, where the expansion of road networks increases access to remote forests that act as refuges for biodiversity ( [[#Campbell--2017|Campbell et al. 2017]] ) (Box 7.1). Logging is one of the main drivers of road construction in tropical forests ( [[#Kleinschroth--2017|Kleinschroth and Healey 2017]] ) which leads to more severe long-term impacts that include increased fire incidence, soil erosion, landslides, and sediment accumulation in streams, biological invasions, wildlife poaching, illicit land colonisation, illegal logging and mining, land grabbing and land speculation ( [[#Laurance--2009|Laurance et al. 2009]] ; [[#Alamgir--2017|Alamgir et al. 2017]] ).

<div id="box-7.1" class="h2-container box-container"></div>

<span id="box-7.1-case-study-reducing-the-impacts-of-roads-o-n-deforestation"></span>