2024-10-21 14:55:00
With global warming, more and more homes are affected. When they are built on clay soils, which swell and contract depending on the water they contain, cracks can appear in the walls, posing a real safety problem for residents. What resources will be needed to mitigate this effect of climate change?
Increasingly widespread, the phenomenon of cracked houses can be explained by a mechanism occurring during periods of drought: clay shrinkage-swelling (RGA). When clay soils dehydrate, they contract, which sometimes causes significant damage to buildings.
The two key factors in the appearance of these cracks are therefore the presence of clay soil and the recurrence of drought episodes. If the nature of the soil depends on immutable geological characteristics, droughts, for their part, are more and more frequent due to climatic disturbances caused by human activities.
These episodes of drought can be considered as negative externalities: collateral effects of economic activities, not taken into account by the responsible actors.
What is the impact of this phenomenon? And what lessons can be learned from the phenomenon of cracked houses to better collectively manage the future consequences of climate change?
Cracked houses: an unequal and growing phenomenon
The Geological and Mining Research Bureau (BRGM) estimates that 48.5% of the territory is in medium or high exposure to RGA. The phenomenon of cracked houses is therefore of national importance.
BRGM
It is also growing strongly. The following figure represents the evolution of the number of natural disasters for droughts and land movements resulting from drought and soil rehydration, two categories of disasters to be compared to the RGA.
Assisted management of administrative procedures relating to risks (GASPAR), Provided by the author
We see, on the one hand, that droughts follow a certain periodicity at intervals of around ten years, with a first cycle which ends at the beginning of the 2000s, a second which ends around 2014 and a third which has not yet reached its end. On the other hand, the number of occurrences increases very sharply in the last observed cycle, as illustrated by the 10-year rolling average shown in blue. Drought being the main cause of RGA, such an increase in drought episodes can only aggravate the phenomenon of cracked houses.
However, this phenomenon is very unevenly distributed across the territory, since it depends on the constitution of the soil. This heterogeneity is also coupled with patrimonial heterogeneity. According to the estimate carried out by the Statistical Data and Studies Service (SDES) in 2021, 10,430,299 housing units would be at medium to high risk of RGA. However, strong differences exist depending on the type of property. Nearly 45% of the exposed housing was built after 1975 and are more vulnerable than older buildings.
Heterogeneous exposure to hazard makes it difficult to develop and implement a national policy, which, by definition, is intended to apply to everyone and across the entire territory.
However, this difficulty seems to be common to many consequences of climate change (increase in temperatures in cities and pollution, increase in water levels, difficulty with localized agricultural crops such as vines, etc.). The public policy treatment of RGA can serve as a model for the issues that will need to be managed.
The economic consequences and the solutions implemented
The appearance of cracks generates significant repair and rehousing costs. The preferred solution so far is financial compensation through private insurance or public funds. However, these solutions do not seem to be enough and, from a strongerwill not be adapted to the future consequences of climate change.
All the recent reports from major public institutions are concerned about the inability of the natural disaster compensation system, known as “CatNat”, to deal with the consequences of climate change. This system allows individuals, businesses and communities to be compensated in the event of a situation declared a natural disaster. In particular, Christine Lavarde emphasizes in son rapport d’information to the Senate that “it is estimated that the cumulative cost of drought losses between 2020 and 2050 would represent a cost of 43 billion euros, a tripling compared to the previous three decades. The CatNat regime would therefore no longer be able to release enough reserves to cover losses by 2040.”
Therefore, other solutions must be considered, for example:
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An increase in resources associated with the CatNat system at the cost of a reduction in funds allocated to other public programs or an increase in levies to spread the cost of the phenomenon across the entire community.
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A change in construction standards to reduce the risk of cracks appearing. This solution is highlighted in the Ledoux report dedicated to the RGA and which is structured around three axes: reduction of occurrence, adaptation of the care of victims and adaptation of housing to climate change.
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An overhaul of the real estate market to adapt to new climatic realities. Some countries, where housing is highly exposed to natural hazards, have implemented models different from ours. In Japan, for example, real estate value is based primarily on the land, while the houses themselves, relatively inexpensive because they are mostly built of wood, are often destroyed and rebuilt every 20 to 30 years. This also makes it possible to renew the real estate stock with very recent constructions and therefore very efficient from an energy point of view.
Furthermore, solutions that simply compensate for the damage do not take into account the reduction in the value of real estate. The probability of RGA, even if the house is not cracked, is integrated by potential buyers and has a direct impact on the market price. According to our estimates, a 1% increase in exposed surface area in the municipality leads, on average, to a significant reduction in the price per square meter of 29 euros. Taking this shortfall into account would further increase the amounts to be paid…
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