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

=== 4.9.1 Urban green infrastructure ===

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Over half of the world’s population now lives in towns and cities, a proportion that is predicted to increase to about 70% by the middle of the century (United Nations 2015 <sup>[[#fn:r1226|1226]]</sup> ). Rapid urbanisation is a severe threat to land and the provision of ecosystem services (Seto et al. 2012 <sup>[[#fn:r1227|1227]]</sup> ). However, as cities expand, the avoidance of land degradation, or the maintenance/enhancement of ecosystem services is rarely considered in planning processes. Instead, economic development and the need for space for construction is prioritised, which can result in substantial pollution of air and water sources, the degradation of existing agricultural areas and indigenous, natural or semi-natural ecosystems both within and outside of urban areas. For instance, urban areas are characterised by extensive impervious surfaces. Degraded, sealed soils beneath these surfaces do not provide the same quality of water retention as intact soils. Urban landscapes comprising 50–90% impervious surfaces can therefore result in 40–83% of rainfall becoming surface water runoff (Pataki et al. 2011 <sup>[[#fn:r1228|1228]]</sup> ). With rainfall intensity predicted to increase in many parts of the world under climate change (Royal Society 2016 <sup>[[#fn:r1229|1229]]</sup> ), increased water runoff is going to get worse. Urbanisation, land degradation and climate change are therefore strongly interlinked, suggesting the need for common solutions (Reed and Stringer 2016 <sup>[[#fn:r1230|1230]]</sup> ).

There is now a large body of research and application demonstrating the importance of retaining urban green infrastructure (UGI) for the delivery of multiple ecosystem services (DG Environment News Alert Service, 2012; Wentworth, 2017 <sup>[[#fn:r1231|1231]]</sup> ) as an important tool to mitigate and adapt to climate change. UGI can be defined as all green elements within a city, including, but not limited to, retained indigenous ecosystems, parks, public greenspaces, green corridors, street trees, urban forests, urban agriculture, green roofs/walls and private domestic gardens (Tzoulas et al. 2007 <sup>[[#fn:r1232|1232]]</sup> ). The definition is usually extended to include ‘blue’ infrastructure, such as rivers, lakes, bioswales and other water drainage features. The related concept of Nature-Based Solutions (defined as: ''living solutions inspired by, continuously supported by and using nature, which are designed to address various societal challenges in a resource-efficient and adaptable manner and to provide simultaneously economic, social, and environmental benefits'' ) has gained considerable traction within the European Commission as one approach to mainstreaming the importance of UGI (Maes and Jacobs 2017 <sup>[[#fn:r1233|1233]]</sup> ; European Union 2015 <sup>[[#fn:r1234|1234]]</sup> ).

Through retaining existing vegetation and ecosystems, revegetating previous developed land or integrating vegetation into buildings in the form of green walls and roofs, UGI can play a direct role in mitigating climate change through carbon sequestration. However, compared to overall carbon emissions from cities, effects will be small. Given that UGI necessarily involves the retention and management of non-sealed surfaces, co-benefits for land degradation (e.g., soil compaction avoidance, reduced water runoff, carbon storage and vegetation productivity (Davies et al. 2011 <sup>[[#fn:r1235|1235]]</sup> ; Edmondson et al. 2011 <sup>[[#fn:r1236|1236]]</sup> , 2014 <sup>[[#fn:r1237|1237]]</sup> ; Yao et al. 2015 <sup>[[#fn:r1238|1238]]</sup> ) will also be apparent. Although not currently a priority, its role in mitigating land degradation could be substantial. For instance, appropriately managed innovative urban agricultural production systems, such as vertical farms, could have the potential to meet some of the food needs of cities and reduce the production (and therefore degradation) pressure on agricultural land in rural areas, although thus far this is unproven (for a recent review, see Wilhelm and Smith 2018).

The importance of UGI as part of a climate change adaptation approach has received greater attention and application (Gill et al. 2007 <sup>[[#fn:r1239|1239]]</sup> ; Fryd et al. 2011 <sup>[[#fn:r1240|1240]]</sup> ; Demuzere et al. 2014 <sup>[[#fn:r1241|1241]]</sup> ; Sussams et al. 2015 <sup>[[#fn:r1242|1242]]</sup> ). The EU’s Adapting to Climate Change white paper emphasises the ‘crucial role in adaptation in providing essential resources for social and economic purposes under extreme climate conditions’ (CEC, 2009, p. 9). Increasing vegetation cover, planting street trees and maintaining/expanding public parks reduces temperatures (Cavan et al. 2014 <sup>[[#fn:r1243|1243]]</sup> ; Di Leo et al. 2016 <sup>[[#fn:r1244|1244]]</sup> ; Feyisa et al. 2014 <sup>[[#fn:r1245|1245]]</sup> ; Tonosaki and Kawai 2014 <sup>[[#fn:r1246|1246]]</sup> ; Zölch et al. 2016 <sup>[[#fn:r1247|1247]]</sup> ). Further, the appropriate design and spatial distribution of greenspaces within cities can help to alter urban climates to improve human health and comfort (e.g., Brown and Nicholls 2015 <sup>[[#fn:r1248|1248]]</sup> ; Klemm et al. 2015 <sup>[[#fn:r1249|1249]]</sup> ). The use of green walls and roofs can also reduce energy use in buildings (e.g., Coma et al. 2017 <sup>[[#fn:r1250|1250]]</sup> ). Similarly, natural flood management and ecosystem-based approaches of providing space for water, renaturalising rivers and reducing surface runoff through the presence of permeable surfaces and vegetated features (including walls and roofs) can manage flood risks, impacts and vulnerability (e.g., Gill et al. 2007 <sup>[[#fn:r1251|1251]]</sup> ; Munang et al. 2013 <sup>[[#fn:r1252|1252]]</sup> ). Access to UGI in times of environmental stresses and shock can provide safety nets for people, and so can be an important adaptation mechanism, both to climate change (Potschin et al. 2016 <sup>[[#fn:r1253|1253]]</sup> ) and land degradation.

Most examples of UGI implementation as a climate change adaptation strategy have centred on its role in water management for flood risk reduction. The importance for land degradation is either not stated, or not prioritised. In Beira, Mozambique, the government is using UGI to mitigate increased flood risks predicted to occur under climate change and urbanisation, which will be done by improving the natural water capacity of the Chiveve River. As part of the UGI approach, mangrove habitats have been restored, and future phases include developing new multi-functional urban green spaces along the river (World Bank 2016 <sup>[[#fn:r1254|1254]]</sup> ). The retention of green spaces within the city will have the added benefit of halting further degradation in those areas. Elsewhere, planning mechanisms promote the retention and expansion of green areas within cities to ensure ecosystem service delivery, which directly halts land degradation, but are largely viewed and justified in the context of climate change adaptation and mitigation. For instance, the Berlin Landscape Programme includes five plans, one of which covers adapting to climate change through the recognition of the role of UGI (Green Surge 2016 <sup>[[#fn:r1255|1255]]</sup> ). Major climate-related challenges facing Durban, South Africa, include sea level rise, urban heat island, water runoff and conservation (Roberts and O’Donoghue 2013 <sup>[[#fn:r1256|1256]]</sup> ). Now considered a global leader in climate adaptation planning (Roberts 2010 <sup>[[#fn:r1257|1257]]</sup> ), Durban’s Climate Change Adaptation plan includes the retention and maintenance of natural ecosystems, in particular those that are important for mitigating flooding, coastal erosion, water pollution, wetland siltation and climate change (eThekwini Municipal Council 2014 <sup>[[#fn:r1258|1258]]</sup> ).

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