Artificialization of soils: the perverse effects of all-out construction

Biodiversity is undergoing massive and rapid erosion: 1 million animal and plant species are now threatened with extinction according to the latest IPBES report. Among the main causes is the artificialisation of land caused by urban sprawl and diffuse constructions, which destroy natural habitats and ecological continuities. There is an urgent need to curb this phenomenon and, if possible, to renaturalize artificial land. Within the framework of the "biodiversity plan", presented by the government last summer, France Stratégie proposal form in that sense. Reaching the objective of "zero net artificialisation" of soils is possible but requires very ambitious measures: the aim is to reduce building artificialisation by 70 % by 2030.

 

Che loss of biodiversity is an "unprecedented decline" in which land artificialisation is a major contributor: urban sprawl and diffuse construction are destroying natural habitats and the ecological continuities necessary for wildlife to move about. It is therefore becoming urgent to curb the artificialisation of land and to renature some of it where possible.

This is the ambition of the "zero net artificialisation" (ZAN) objective set out in biodiversity plan presented by the government in the summer of 2018. A goal that the biologist Julien Fosse(FR) The rapporteur, Mr Blair, considers that a report for France Stratégie is achievable, provided that the town planning rules are amended and the housing stock is densified.

 

The loss of natural, agricultural or forest areas (ENAF), tarred car parks, warehouses, buildings, roads, railway networks, housing estates ... all this leads to the process of soil artificialisation. There is no such thing as artificialisation, but rather multiple processes with different impacts on the environment. In France, according to cadastral data, 3.5 million hectares are now artificialised, which represents 6.3 % of the metropolitan territory, a higher share than in our main neighbours, when compared to population density. Every year, this represents an additional 20,000 hectares of artificial land. At this rate by the end of the century, 18 % of the territory will be artificialized, notifies IDDRI (Institute for Sustainable Development and International Relations).

 

The demographic factor plays an important but partial role, with the dynamics of artificialisation proving to be faster than population growth. The French preference for individual housingThe development of the transport sector, which leads them to settle further and further away from city centres and involves the deployment of transport infrastructure, also contributes to this dynamic. Depending on the sources, the average rate of artificialisation for France varies, for example, from 16,000 to 61,000 hectares per year. However, the data converge to show that in France, artificialisation is higher than the European average and is increasing faster than the population.

Added to this are the strategies for setting up businesses on the outskirts of urban centres to benefit from cheaper land. Finally, policies to support new housing can also encourage urban sprawl. 

 

To complete the elements of the demographic factor, the increase in the population and even more so in the number of households - + 4.2 million since 1999 - is far from justifying in itself the progressive nibbling of natural areas. Rather, the explanation lies in the trade-offs made by the actors.

Municipalities, for example, have an overall interest in attracting activity on their territory, and therefore in building, especially since the property tax on built property - 41 billion euros in 2017 - is an important resource in a constrained budgetary context. 41 billion in 2017 - is an important resource in a constrained budgetary context. This is an incentive that policies to support the real estate sector and home ownership (interest-free loans, Pinel scheme) can in some cases strengthen.

Households in France, for their part, show a clear preference for individual housing, which they now tend to seek on the outskirts of major urban centres. Yesterday's default choice is now (for some) a positive choice, that of space and proximity to nature, made possible in particular by the lower cost of commuting by car. Finally, the differential in land prices and local taxation between the centre and the periphery can encourage companies to locate part of their activities in the immediate vicinity of urban centres, warehouses or commercial zones for example.

 

These trends are converging: peri-urbanization, the "loosening of cities" and the low density of new construction (single-family housing in particular) are contributing to urban sprawl and thus to the progression of artificialization. This sprawl is accompanied by "territorial sprawl" - a term used to describe the diffuse scattering of housing and buildings over an initially rural area. Land sprawl is encouraged by the low value of the French agricultural hectare (one of the lowest in Europe), compared to the value of land available for urbanisation.

 

Finally, an aggravating factor: the high level of land artificialisation in France can also be explained by the under-exploitation of existing buildings (empty homes and offices) and by the development of second homes occupied intermittently (residences which represented 9.5 % of housing in 2015).

 

Another problem, and not the least of the artificialisation of the land, is the repercussion on food. According to Emmanuel Hyest, president of the Sociétés d'aménagement foncier et d'établissement rural (Safer), the consequences could also be terrible in terms of agriculture: "... the consequences for the food sector are not only on the land itself, but also on the environment. Firstly, it would mean a loss of food autonomy in France at a time of population growth; secondly, agricultural land is helping to combat climate change. They capture carbon but also the water that recharges the water tables.« . For Emmanuel Hyest, it is absolutely necessary to consider agricultural land as untouchable surfaces, like forests. If you put concrete in place, water no longer circulates or irrigates, while paradoxically increasing the risk of flooding.

 

Even beyond the possible irreversible effects of soil pollution, renaturing artificial land is a complex and costly process. According to IDDRI, the objective of "zero net artificialisation", introduced in the 2018 Biodiversity Plan, "... is a major step towards the achievement of the goal of "zero net artificialisation". assumes that any new construction should be compensated by equivalent deconstruction, for example in vacant business parks or oversized car parks « . This requires deconstructing, depolluting, dewatering and then (re)constructing "technosols", with the last three stages of the process alone costing up to 400 euros per square metre.

 

It is therefore urgent to curb artificialization. All the more so because, if no measures are taken, an additional 280,000 hectares of natural areas will be artificialised between now and 2030, i.e. a little more than the surface area of Luxembourg for comparison. « A catastrophic trend scenario "Julien Fosse, who used an econometric model developed by the Commissariat général au développement durable (CGDD) to achieve this result.

This model makes the consumption of natural areas dependent on three variables: built area, urban renewal rate and housing density (which roughly corresponds to the land use coefficient). Advantage: it allows alternative scenarios to be projected (excluding transport infrastructures not included in the land register).

In the "high densification scenario", for example, the author calculates that the increase in the urban renewal rate (from 0.43, the current 0.6) combined with the increase in the housing density rate (from 0.16, the current 0.4) would make it possible to reduce the consumption of natural areas to 5,500 hectares per year by 2030, compared to 20,000 in the trend scenario. « This result highlights the significant role that an urban planning policy that promotes the renewal and densification of housing could play in the fight against artificialization. ", says the author.

 

In a complementary scenario, to the tightening of urban planning rules is added the increase in the price of land with a price multiplied by 5, and a decrease in the vacancy rate of dwellings from 8% (in 2015) to 6 %. This scenario would make it possible to further reduce the surface area of artificial land to 3,700 hectares per year by 2030, but it would call for measures that would be difficult to implement in practice. The "high densification scenario" seems, on the other hand, much more accessible.

 

The introduction of measures aimed both at slightly densifying areas already built and at doubling the land use coefficient of buildings on nonartificialized areas would make it possible to greatly reduce artificialization, without reducing construction. By 2030, such a "high densification" scenario would make it possible to save nearly 15,000 hectares of natural, agricultural and forest areas annually.  

 

If these measures were combined with a policy of increasing the price of vacant land and reducing the number of vacant houses, the annual saving of natural, agricultural and forest areas by 2030 could reach a little over 16,000 hectares. However, this last "complementary" scenario is hardly conceivable.

 

Consideration should also be given to refocusing the Pinel and zero-interest loan schemes on these already built-up areas, in order to limit the incentive to build-up that these schemes designed to encourage new construction or facilitate home ownership may have. Making the planning instruments consistent - with each other and with the objective of zero net artificialisation - will require dedicated governance at different territorial scales.

Finally, mechanisms to make soil artificialisation conditional on equivalent renaturation - markets for the right to artificialisation or malus on artificialisation to finance renaturation - should be studied. 

 

This modelling exercise suggests that achieving "zero net artificialisation" by 2030 would require a reduction of 70 % in gross artificialisation and the renaturation of 5,500 hectares of artificialised land per year. A perspective that assumes " far-reaching measures ", concludes Julien Fosse.

 

By setting a target of zero net soil artificialisation, France is a pioneer in Europe. To achieve this goal, it is necessary to start by collecting robust data on artificialisation and the cost of renaturation, and to set up dedicated governance. Merging the missions of the Departmental Commission for Commercial Development and the Departmental Commission for the Preservation of Natural Spaces would, for example, make it possible to create a "network" for the preservation of natural areas. departmental council for the fight against land artificialisation The author proposes that the "open to all relevant stakeholders and responsible for the prior issuance of authorizations for artificialization".

It is then necessary to reflect on the adjustment of fiscal and regulatory tools, which are likely to have a far-reaching effect.

 

In order to curb gross artificialisation, measures to increase the density of new buildings can also be considered. In this regard, "the the setting of minimum building densities in the PLU [local urban plan] seems to be the most promising one ", says the author. Policies to support new housing, one of the most promising avenues, consist of introducing a minimum land use coefficient into local urban planning and setting a minimum share of new construction to be carried out on already artificial areas. Finally, residual artificialisation should be accompanied by renaturation operations.

 

So nothing is impossible in the objective of the biodiversity plan... but the densification of the habitat and the limitation of urban sprawl mean that we have to review at a minimum our town-planning rules.

Source Report by Julien Fosse for France Stratégie - July 2019

 

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