Urbanization is transforming land formerly used by agriculture or as a natural area into artificial and sealed surfaces. The impermeabilisation of surfaces, as a consequence of increasing urbanization, leads to loss of essential surfaces for rain water infiltration. The climate change brings the increase of extreme weather events including heavy rains. As a consequence, there will be an increase in flash floods in cities. Sealed surfaces contribute to the urban heat island effect. Besides contributing, it is also hampering the opportunity to fight urban heat islands via more green areas in our cities. Vegetated surfaces can provide food as well as regulate the local climate (water infiltration, regulation of water courses and runoff, and as a support for vegetation, absorption of the greenhouse gases and other services provided by vegetation). Due to these processes, reduction of ecosystem services due to impermeabilisation and land consumption affects also the areas surrounding the impermeabilised sites. By reducing connectivity between ecosystems their capacity of delivering ecosystem services is compromised, for instance by reducing the capacity of mitigating urban heat island effects. Although the overall quantities of impermeabilized soil, with 2.74% in Italy and 1.23% in Croatia, (EEA 2021), or 2.64% for the European mean may seem low (values for 2015: https://www.eea.europa.eu/data-and-maps/indicators/imperviousness-change-2/assessment, acsessed 15/02/2021), recent investigations have calculated that in Italy in 2018 three quarters of the territory are within the range of 200 m from impermeabilised soil. (Munafò 2019, 143), while the rate of the areas with high and very high fragmentation was 39% of the national territory (Munafò, 2019, 147). Having in mind that the percentage of built-up in the coastal zone is substantially higher than the national average, the percentage of impermeabilised soil in the coastal zone is among the highest in both countries.
Limiting the consumption of soil and the extension of urban sprawl has become a major concern at the global level. It is part of the Sustainable Development Goals, aiming at a land degradation-neutral world by 2030 (SDG 15.3), reducing the environmental impact of urban sprawl (SDG 11) and contributing to the mitigation of climate change (SDG 13). The European Commission has adopted the goal of achieving net zero soil consumption by 2050 and requests having adequate policies in place to achieve this goal by 2020 (Council of the European Union and European Parliament 2013).
Implementation of such policies at the local level can be a difficult task in the face of continuous demand for new buildings and infrastructures from a local political point of view, despite the benefits offered to the society in terms of conservation of landscape and ecosystem services. Net zero soil consumption can be achieved in various manners, first of all recurring to urban rehabilitation and requalification of underused or derelict areas for new edification, substitution or requalification of existing buildings. Furthermore, soil de-sealing can compensate the soil sealing balance, with the transformation of derelict areas or interstitial spaces into green areas contributing to requalification of soils and recreation of surfaces capable of providing ecosystem services to urban dwellers.
Support from higher governance levels can help trigger action at the local level. In Italy, several regional planning laws have introduced the goal of net zero soil consumption by 2050 and introduced rules and instruments for reducing new land consumption. Among such instruments, the Emilia Romagna Region, while establishing the goal of achieving the zero-soil consumption by 2050, has limited the possibility of creating new urban expansion areas to a maximum of 3% of the urbanized part of the territory of a single municipality. The law foresees also mechanisms of equalization at the territorial level – for instance within associations of local authorities – poses limitations to urban sprawl and offers incentives for urban regeneration, restoration and substitution of the existing buildings. In a similar manner, also the Veneto and the Friuli Venezia Giulia regions have introduced the goal of urban renewal and rehabilitation as a means for reducing further extensions of urban areas, introducing, in the case of Veneto, a limit for new urbanizations and their distribution across the local areas of the region (Munafò 2019, 28). In the Lombardy region, where the regional law invites all local authorities to review their plans and reduce the plans for new urbanization, the town of Rescaldina has approved a new urban plan which does not foresee new, and has completely cancelled the previously foreseen extension areas (Munafò 2019, 195).
Inside urban areas, creation of green spaces and corridors and de-sealing can contribute to reduction of urban run-off. Good practice examples for de-sealing of urbanized areas can be found in https://www.sos4life.it/.
Costs and benefits
The costs of administrative measures for the reduction of the existing and the limitations of new building areas are limited to the cost of procedures inherent to the planning process.
For de-sealing an urban space,the city of Cervia has estimated the costs of removing soil sealing materials alone for approximately 16-20 €/m2, including recycling of material, and eventually further 5€/m3 which might be necessary for the excavation of existing road foundations.
The realization of draining pavements is accounted for with 45-60 €/m3 for the creation of the filtering substrate, and further 70-80 €/m2 for the realization of a new draining pavement.
For the greening of a surface of 1600m2, further to the cost of supplying and layering new soil substrate (8 €/m2), as de-sealed soils normally are not fertile, the following costs needed to be accounted for: supply and laying of bushes and shrubs (approximately 8 plants per m2, at a cost of 8€ per plant, resulting in 48-50€/ m2) and planting of 60 trees at a cost of 300€ each resulting in 10€/ m2 for tree planting. The installing of drip irrigation systems accounts for further 10 €/ m2.
Among the benefits, the avoided costs and losses related to urban surface flooding and those resulting from reduced rates of overheating in urban public should be accounted for, which depend on the specific local conditions.
Implementation time and lifetime
Implementation time of strategic measures such as reducing the surface for building activities in local plans is connected to the preparation and implementation of such plans. In the case of de-sealing of formerly sealed surfaces, the time for design and implementation is short (several weeks or months) and there is no limit to the lifetime of such de-sealed areas.
Source for more detailed information
Sos4Life Save Our Soil for Life project (https://www.sos4life.it/en/)
Council of the European Union, and European Parliament. 2013. Decision No 1386/2013/EU of the European Parliament and of the Council of 20 November 2013 on a General Union Environment Action Programme to 2020 ‘Living Well, within the Limits of Our Planet.’ 1386/2013/EU. Vol. L 354/171. http://data.europa.eu/eli/dec/2013/1386/oj.
Munafò, Michele. 2019. “Consumo di suolo, dinamiche territoriali e servizi ecosistemici.” Report SNPA 08/19. Roma: Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA). https://www.snpambiente.it/wp-content/uploads/2019/09/Rapporto_consumo_di_suolo_20190917-1.pdf.
SOS4LIFE. 2020a. “Liberare Il Suolo 1. Linee Guida per Migliorare La Resiliene Ai Cambiamenti Climatici Negli Interventi Di Rigenerazione Urbana.” Bit.ly/LIBERARE-IL-SUOLO-1.
———. 2020b. “Liberare Il Suolo 2. 20 Casi Studio per La Resilinza Urbana: Progetti e Processi Di Adattamento Negli Interventi Di Rigenerazione.” Bit.ly/LIBERARE-IL-SUOLO-2.
Presentation of the SOS4Life Guidelines https://www.youtube.com/watch?v=GcWkBsbyi9c&feature=youtu.be. (in Italian)
Contributors and contacts:
Luisa Ravanello, ARPAE (SOS4LIFE 2020a) <email@example.com>