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Xynthia: lessons learned from a catastrophe

Xynthia : leçons d’une catastrophe
Etienne Chauveau, Céline Chadenas, Bruno Comentale, Patrick Pottier, Amandine Blanlœil, Thierry Feuillet, Denis Mercier, Laurent Pourinet, Nicolas Rollo, Ion Tillier y Brice Trouillet
Traducción de Emma Maisonnave
Este artículo es una traducción de:
Xynthia : leçons d’une catastrophe

Resúmenes

The storm Xynthia occurred on the 28th of february 2010. It has been one of the most deadly seen on the French territory since several decades, with 47 victims, half of them found on the department of Vendée. We suggest a global interpretation of the reasons of the disaster on two adjoining districts, in the south of this department, La Faute-sur-mer and L’Aiguillon-sur-mer. We first focus on the different natural hazard’s characteristics: wind’s strength, role of the high tide’s coefficients, topography of the affected coastal areas, particularly on enclosed bays and estuaries, constitute risk factors which have add their effects in time and space, creating strong uplifts of sea level. We then analyse the crisis development, which partially explains the vulnerability of specific areas. Following, the first economic consequences on submerged lands are presented. Finally, we point the lack of risk assessment, resulting from long and carelessness practices on territorial management, to the detriment of natural processes knowledge and constraints, especially on potentially submerged areas. The lack of risk awareness has persisted with decisions taken locally, as well as at the highest national politic power.

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Introduction

1Storm Xynthia, which occurred on February 28th 2010, was one of the deadliest seen in France in the past decades. To the human toll (47 deaths) can be added a cost estimated in September 2010 at 1.5 billion euros by the French Federation of Insurance Companies (FFSA), including 700 million euros of damages caused by the floods to be compensated. The number of registered compensations concerned 40,000 goods. Due to the conjunction of several natural elements (heavy swell, direction of the wind, atmospheric pressure, etc.), the two most affected departments were Charente Maritime and Vendée. In this article, we will analyze and try to list the physical and human factors that can justify the significant damages experienced by two coastal cities in the south of Vendée, La Faute-sur-Mer and l'Aiguillon, the two most impacted towns by far (29 victims in La Faute-sur-Mer). We will base our analysis on former studies carried out on the area by geographers mainly from Nantes, and on the issue of coastal urbanization.

2In order to do this, we will reflect upon the elements linked to i) the evaluation of the importance and of the characteristics of the hazard, ii) the vulnerability of the affected territories in relation to the issues that characterize them, and iii) the more or less long term risk management, in the area under study as well as in the national context. The socio-economic consequences presented only concern primary activities.

A hazard turned extreme due to the temporal conjunction of more or less rare natural events

3The anxiety provoked by the gradually increasing macabre toll on the day following the storm brought into focus the exceptional nature of the event. Was this really the case?

The storm of February 27th and 28th 2010

  • 1 Monthly weather report, February 2010, Charente-Maritime, n°62, 4 p: atmospheric pressure at sea le (...)

4Storm Xynthia is an event that was caused by the interactions between the energy meridians in the whole northern hemisphere. Although it was linked to a strong depression (fig. 1: 977 hectopascals (hPa)1 in La Rochelle during the night between February 27th and 28th 2010), it did not have an unprecedented nature in terms of meteorology; its destructive nature is due to its combination with strong tidal movements, something which had been signaled.

5According to Météo-France2, storm Xynthia spawned from an Atlantic atmospheric depression formed in very low latitudes (near the Tropic of Cancer), and which intensified in the morning of February 27th when moving towards Madeira. It moved rapidly: centered near the north-east of the Iberian coast on 27/02 at noon UTC (980.3 hPa in Coruña; 981.2 hPa in Porto, according to the Météo-Hebdo weather report), it swept across north-western France during the night of February 27th to 28th before moving to the west of Belgium and the Netherlands at noon UTC on 28/02 (974.8 hPa in Brussels, fig. 1). This was therefore a high energy event, of an “unusual size and intensity for the end of winter”, but actually quite “common” in terms of seasonal energetic interactions in the northern hemisphere3.

6What is at stake in this article are the mechanisms that led to the transformation of a depression into a storm. The pressure drop was rapid, 11 hPa in 14 hours, between the observation on 27/02 and the sweep across the French Atlantic coast during the following night. It can be compared to the 14 hPa drop in 12 hours that was noted for the storm on February 2nd 1990 (Tonnerre-Guérin, 2003).

7The reference works by M-A. Tonnerre (2001) on the storms that hit the French western coast underline the role of hot invasions that move far in latitude and contribute to the development of a trough of warm air aloft (trowal). This situation was observed on 27/02 (12:00 UTC): the Xynthia depression was formed at the front of a trowal on the left side of the rectilinear jet stream (south-westerly winds of about 500 hPa: 75 knots in Coroña, 100 knots in Madrid); this depression was coupled with an ascent of warm air in altitude (-16°C) on the Iberian peninsula and the Bay of Biscay. This caused the brutal confrontation between warm and humid air (in Porto, ground temperature (“wet bulb”) was of 13°C, with an ambient air temperature of 16°C) located at the front the depression, and cold air (-32°C) at the back, and can explain the intensification of the depression. It accounts for its rare nature, if compared to the normal coupling mechanisms between surface depressions and low geopotential heights observed further north, between Ireland and Iceland in a sector unreachable by hot incursions (less dense depressions – 980 to 990 hPa – associated to geopotentials between 5,080 and 5,160 meters).

8All in all, wind speeds reached 130 km per hour near the coast of Vendée (and wind gusts up to 158 km/h in the west end of Ile de Ré). This was not as strong as in January 2009 when winds of about 150 km/h had devastated the Landes forest (winds of 184 km/h were recorded in Perpignan), and especially as in December 1999 when peaks of over 160 km/h were recorded in certain parts of the Atlantic coast (Oléron Island) and of over 170 km/h in the Paris region. Considering this recent series of intense storms, it is relevant to question the evolution of their frequency over a longer period of time.

The evolution of storms in La Rochelle between 1958 and 2009

9The evolution of storms on a national scale is assessed by using the maximum instantaneous wind speed in La Rochelle on a daily basis (altitude: 4 meters, latitude: 46°09'12''N, longitude: 01°09'24W) between 1958 and 2010 (data from Météo France). By taking into consideration the Beaufort scale, we came up with three categories of winds, similar to those of Bessemoulin (2002): winds superior to 89 km/h (storm), to 102 km/h (severe storm) and to 118 km/h (hurricane). Since 1958, la Rochelle has experienced 343 days of storms, 94 days of severe storms and 28 days with winds superior to 118 km/h. The maximum speed (162 km/h) was measured on December 16th 1958. 22 of these 28 days occurred in the winter time (between December and March). Wind speeds superior or equal to those seen during storm Xynthia (132 km/h in La Rochelle) were recorded seven times in this time span, an average of once every seven years. Figure 2 represents the evolution of the number of these days per year over the whole period (51 years). The tendencies vary according to the category of wind. By applying the Mann-Kendall test (Mann, 1945, Kendall, 1975, Hipel and McLeod, 1994), we observe that the number of stormy days (winds superior to 89 km/h) has decreased, as well as the number of days with severe storms (winds superior to 102 km/h).

10However, the number of days with winds superior to 118 km/h are randomly distributed (no significant tendency was detected), which is consistent with Dreveton's conclusions (2002) for France. This lack of tendency is linked to a strong interannual variability of severe storms. Calm phases (only one day with winds exceeding 118 km/h between 1983 and 1995) alternate with phases of recurrent storms (six great winds between 1958 and 1961 and five since 2006).

11These tendencies can be surprising in these times of climate modelling that forecast the intensification of storms, a global rise of temperatures and more extreme rainfall intensities. Nevertheless, on a “regional” scale (that of France for IPCC climatologists), the results of a finer modelling provide a more nuanced picture. The French climatic scenarios portray a reduction of the number of storms in mid-latitudes of the northern hemisphere and the stagnation or increase of severe storms (Dufresne et al, 2006). However, complementary research in space and time is essential to draw accurate conclusions.

12The dramatic turn of events with Xynthia is linked to the conjunction of unfavorable factors (a high tidal coefficient and unpredictable storm surge, etc.); it would be relevant to compare storm surges between Xynthia and other storms of similar intensity. As Bouligand and Pirazzoli demonstrated in 1999, extreme storm surges tended to augment in Brest between 1953 and 1994. We will now present the causes and effects of these storm surges in the area under study.

The fateful conjunction of factors leading to the storm

13With Xynthia, the conjunction on a very short period of time of high tidal coefficients (102), high tides and westerly winds with maximum speed, led to storm surges (over +1.53 meters measured in La Rochelle). The configuration of the coastline and the underwater morphology also need to be taken into consideration. The coastline between La Tranche-sur-Mer in the north and the area facing the southern part of Oléron island, with its entrenched bays (Bay of l'Aiguillon) and the existence of Ré island and Oléron island, provided an ideal configuration for storm surges. The flat underwater topography that runs far from the coast increases this risk of storm surge (Fig. 3). Moreover, the direction of the winds constituted a significant factor for storm surge, as they were south-southwesterly at 1 am, before going westerly at 4 am.

14The towns of La Faute and l'Aiguillon had an additional aggravating factor: the mouth of the Lay River. Shaped like a large funnel, it separates the peninsula of Arçay Point in the west from the lower shoreline where l’Aiguillon is located in the east. At the river mouth, even if the tide is not rising, water inflow from the continent creates an additional increase of the water level in the estuary: marine incursions block the usual evacuation of freshwater. When the storm happened, the Lay River was not swelling. The monthly average in February 2010 (19.5 m3/s) was inferior to the average recorded in the months of February during the past six years of observation (25.5 m3/s), and much lower than the most abundant month of February (63 m3/s). Concerning daily flow rates, they were low during the days preceding the disaster: 48 m3/s on February 26th 2010, 30 m3/s on the 27th. In comparison, the maximum daily flow rates observed on the Lay River since 2004 reached 210 m3/s on January 16th 2008. This factor played a role in mitigating the disaster; this was also the case for bigger rivers nearby, the Sèvre niortaise and the Charente.

15The area of La Faute-sur-Mer which was flooded on February 28th 2010 corresponds to the topographically lowest part of the town, located alongside the Lay estuary and not near the Atlantic Ocean. The sea surged up in the Lay estuary and flooded over without rupturing the embankment built to protect La Faute-sur-Mer. It however created a breach in the sand dune in a place known as “la belle Henriette”, further north near the ocean. This is what provoked a pincer effect for the urban zone, trapped between the waters from the bay and those pouring through the breach.

16Storm surges from both the river and the sea were also observed at the mouths of the Sèvre niortaise (in the east), at the end of the bay of l'Aiguillon, and of the Charente (further south). Although these two rivers do not have estuaries and urbanization is not as close to the coast in the first case and often on higher grounds in the second, there were still victims from the storm surge.

17The last significant element is the tidal coefficient. On February 28th, high tide occurred at 4.18 am with a coefficient of 102, three hours after the maximum sustained winds associated with the storm. However, the seven high tides in the three following days were characterized by higher coefficients: 108, 113, 115, 116, 116, 113 and 109. The disaster could therefore have been worse if these winds had blown 24 hours, 48 hours or even 72 hours later.

18To summarize this hazard, although the storm appears to be quite unremarkable, we can still speak of a rare event because it was linked to the conjunction of aggravating factors. The magnitude of the consequences (death toll, extensive damage to houses and to agriculture, etc.) can be explained by the lack of understanding of the risks. The quality of the short-term forecasts is not the issue and the risk of flooding was known: significant floods in the bay of l'Aiguillon have a return period of thirty years, or one major event for each generation (Garnier and Surville, 2010). This disaster reveals major dysfunctions (irregular maintenance of the embankments, floodplain construction...) and reflects the lack of understanding of the risks in an area where vulnerabilities have increased in the past decades. The term vulnerability can here be defined as “the propensity to be adversely affected” (Meschinet de Richemond, 2010).

Managing the crisis and the first economic consequences

19The conjunction of elements that led to the catastrophe gives us material to comprehend the consequences. It emphasizes the impression of a lack of understanding of the risks on the sectors impacted by the storm, especially with the way the after-crisis was managed from mid-March 2010 onwards.

Managing the crisis

20The pre-crisis started with an alert issued by Météo-France at 4pm on Saturday 27th of February. When analyzing the warning reports, it appears that the consequences of the storm on human activities and equipment were not well understood: the risk of flooding was barely mentioned, although it happened to be the main danger. The reports however insisted on the violence of the winds. As a consequence, the advice that was shared (“stay at home”) was not adapted to the situation of submersion (Report from the Senate no. 554, June 2010). The warning mechanisms were thus not adequate and the responsibility of this warning report should be examined. Various informers (Météo-France, SHOM, Prefecture services) hesitated to take responsibility to give precise instructions to the mayors or to the concerned populations. For this reason, no preventive evacuation was launched.

21The victims alerted the SDIS 85 (Vendée Departmental Fire and Emergency Service) at 3.20 am at St Gilles Croix de vie and at 3.30 am at La Faute-sur-Mer. Over one thousand firefighters came to rescue the victims with helicopter and boat evacuations. Although the telephone networks were disturbed, the rescue mechanisms functioned well.

  • 4 NGF (Nivellement Général de la France) corresponds to the Ordnance Datum Newlyn in the British Isle (...)

22The micro-topography of the inundated sectors in La Faute and in l'Aiguillon presents differences of altitude between 2m NGF4 for the lowest constructed zones and 4m NGF for the most elevated constructed zones. The expert analyses that were carried out in the days following the catastrophe evaluated the maximum height of the water level to 4.7m NGF. The peaks (between 6 and 9m NGF) were located along the Atlantic ocean, as the longshore drift that created Pointe d'Arcay runs from north to south, and the wind depletion which produced the dunes blows from west to east. All the lower zones in la Faute-sur-Mer, in l'Aiguillon-sur-Mer and in the Marais Breton were flooded under 3 meters of water during Xynthia.

23The most affected area was the town of La Faute-sur-Mer, especially the recent neighborhood constructed behind the embankment that runs along the marina, between Lay Boulevard, Voiliers Street and the road to the yacht port. The municipal camping ground located on the eastern side of the Lay River was completely inundated. The number of victims rose to 29 in La Faute-sur-Mer, 28 of whom were from this neighborhood. The victims, aged 2 to 85, were mainly elderly persons aged over 60 years old.

24The lack of understanding of the risks is revealed by the gap between the quality of the previsions, which left no doubt on the scale of the probable risks, and the absence of anticipation of public authorities in the hours, even days, preceding the disaster. Météo-France had described the intensity of the storm to come: on the eve of the event, four departments had been placed on red alert (including Vendée and Charente-Maritime) and 70 others on orange alert. Moreover, the IFREMER, via its PREVIMER forecast system, had anticipated storm surges in Vendée and in Charente-Maritime very precisely. In these conditions, it is tempting to wonder a posteriori why the evacuation of the populations was not arranged. However, the exceptional nature of Xynthia is due to the temporal conjunction of sometimes interdependent phenomena (wind and depressions), but, when associated to strong waves and high tidal coefficients, engendered significant storm surges. The warning messages taken one by one are not easy to summarize and it was difficult to plan the conjunction of these phenomena. Moreover, should everyone along the coast in the four departments placed on red alert have been evacuated? Only those in Vendée and Charente-Maritime? Or only the towns where people died? On which spatial criteria can we base this evacuation?.

Managing the post-crisis

25The President's speech on March 16th announcing emergency measures was the starting point of the post-crisis management. Two days later, a circular requested for the Prefect of Vendée and Charente-Maritime to proceed to the mapping of “zones of extreme danger”. They were qualified by the press as “black zones” and were renamed “solidarity zones” in April by the State Minister of the Environment and Sustainable Development. A first zoning was addressed to the Ministry of the Environment, Energy, Sustainable Development and Sea on March 21st. Complementary assessments only brought small modifications to this zoning, which means 90% of the mapping of “black zones” was done in the space of a few days, on the basis of rough topographical data (BD Alti), of legal documents and of the estimated speed of water withdrawal in the flooded areas three days after the catastrophe by the BRGM (Bureau of Geological and Mining Researches) and the DDTM 85 (Vendée Departmental Directorate of Territories and the Sea).

26The “black zone” in la Faute-sur-Mer corresponds to the lowest topographic zone. It covers the zone with the most numerous victims (28 out of 29). Certain houses in this “black zone” were not flooded because they were located on higher grounds where sediments had accumulated. The mission report written after the complementary analyses was finished on September 16th 2010. It suggested new perimeters for expropriation, with 472 demolitions in la Faute-sur-Mer and 289 in l'Aiguillon, including 100 lightweight constructions. The total cost of reparations was estimated at 150 million euros, to which must be added the cost for securing the sites at around 18 million euros in la Faute-sur-Mer and 12 million in l'Aiguillon. The total cost therefore reached 180 million euros.

27The concept of “black zone” was created to avoid more victims of maritime flooding. It should be applied a priori and be included in the demarcation of the PRRI perimeters, and not a posteriori. The difficulties to apply this concept, even a posteriori, in a zone with a death toll, demonstrates that it cannot be generalized without reforming the Barnier law of 1995 more than the Bachelot law (2003) did, making consultation for the implementation of PRRI compulsory instead of recommended.

28In the weeks and months following the disaster, the embankments were rapidly consolidated for 2.13 million euros in la Faute-sur-Mer, along the Lay estuary, in order to protect the houses behind it. Let us note that these embankments did not collapse but were submerged during the storm of February 28th. It can therefore seem contradictory to elevate the embankments whilst demolishing the buildings behind them. The argument provided to carry on these works was the protection of the less exposed houses because located on higher ground.

The consequences for the economic activities in the primary sector

29The activities and infrastructures of the primary sector have a significant spatial influence in the area (fig. 4) and the direct employments in this sector represented 9.23% of the active population in the 2006 census. For the fishing and aquaculture sectors, the share of employments linked to primary sector activities reached 16%, which makes it a major socio-economic concern.

Fishing and aquaculture

30The activities linked to the exploitation of maritime resources are important in terms of employment and infrastructures. Shellfish farms have storage and beds on land, and their location near the coastline makes them vulnerable to storm surges such as those provoked by storm Xynthia.

Fig. 4: location of shellfish farms in the l'Aiguillon area

Fig. 4: location of shellfish farms in the l'Aiguillon area

- Shellfish basins on land
- Shellfish farms on land
- Oyster parks
- Long line systems
- Mussel stakes and beds

Fishing

31The first danger was the destruction of these infrastructures. The submerged area was a port (on the small coastal Lay River), sheltered behind Pointe d'Arcay and with very few infrastructures (a few landing stages, a place of disembarkation/transit). This explains why, out of 47 fishing boats from l'Aiguillon-sur-Mer, only four were severely damaged. The port of l'Aiguillon-sur-Mer could no longer function and the few professionals who pursued their activity went to unload in other ports. According to the estimations made by the Economic Interest Group (EIG) of the l'Aiguillon fishermen and by the COREPEM (Regional Committee of Fisheries and Sea Farms of the Pays de Loire, 2010), the average economic loss was superior to 100,000 euros per boat by the end of the eel season.

32Despite the lack of hindsight, the damage made to the marine ecosystem was predictable. Pollution due to accidental oil leakages (fuel and oil tanks), to the leaching of flooded fields and to domestic activity linked to the destruction of sanitation facilities, damaged the environment. According to the monitoring of the National Observation Network of the IFREMER, the nurseries of certain species and shellfish stocks (scallop and oysters) were impacted on the long term.

Shellfish aquaculture

33The Pertuis Breton area of production was one of the most affected by storm Xynthia in terms of proportion of damaged companies (36% after the Marennes-Oléron area with 61% and the Bourgneuf Bay with 48% (SRC – PDL, 2010). 119 shellfish companies had installations in the l'Aiguillon area. They were local companies and companies from the Charente region. Shellfish farming necessitates the use of different areas in the sea, on the foreshore and on land. This separate spatialization of implantations (some onshore, some offshore) mainly explains the type of damages endured by shellfish aquaculture due to storm Xynthia.

34The damages from the storm were mainly due to the storm surge. Onshore installations were the most affected; offshore shellfish farms were spared in comparison with the storm of winter 1999. The techniques of offshore oyster farming using the longline culture system were indeed developed in the bay of Pertuis Breton. Out of 320 longlines5 installed in the Pertuis Breton, only six were cut off, but there were also secondary material losses (buoys, etc.). Mussel cultivation is also very present in the area of production (15,000 tons produced every year, or 20% of French production and 40% of spat collections (data from the National Committee of Shellfish Aquaculture6). The mussel stakes were greatly spared as sea conditions were not rough enough to destroy everything. The current inventory of damaged mussel beds reports between 5 and 10% of losses (Cultures Marines, 2010). Nevertheless, the companies deplore numerous material losses (over 2,000 stakes were ripped out, numerous raid mussels. The production equipment thus underwent damages but the companies did not lose enough shellfish to cease their activities.

35Onshore, the shellfish farms were much damaged. The oyster beds were submerged, which means the maturing phase needed to be done again. The buildings that were not destroyed were flooded. The equipment inside was ruined or damaged, especially graders and binders... A number of utility vehicles was also lost. The loss of equipment stored onshore hence made shellfish farming in the l'Aiguillon-sur-Mer area temporarily impossible.

  • 7 Example of the Prefectoral order n°2010-5366 dating from May 12th 2010 by the Prefecture of Charent (...)

36In addition to the loss of shellfish and of equipment, as for fishing, issues of environmental degradation incited prefectures7 to pass decrees on sanitary closures. The commercialization of shellfish (farmed or wild) was thereby forbidden. Moreover, this sanitary situation, due to the leaching of certain agricultural zones and to the flooding or partial destruction of sanitation infrastructures, prevented shellfish farmers from temporarily converting to inshore fishing (many of them had permits).

Agriculture

37The consequences of storm Xynthia on agriculture, already impacted by diverse recent crises such as the milk crisis, were also significant. The rupture of seawalls and embankments (numerous breaches on the embankment southeast of the Dive and on the Polder, at the northern side of l'Aiguillon Point) led to the flooding of almost 12,000 hectares of agricultural fields in Vendée and over 40,000 hectares in Charente-Maritime, 10% of agricultural land in the department. Among these flooded areas, some of which were 15 km away from the coastline, two thirds were being cultivated (40% of cereals) and a third corresponded to pastures reserved for grazing (Palleau, 2010).

38The damages caused by the rupture of the seawalls and by the subsequent flooding were heavy. Other than the destruction of crops, the destruction of equipment, the loss of livestock and the degradation of the agronomic proprieties of the soil led to significant operating losses. These damages were covered by the insurance against natural disasters (storm coverage). The compensation amounts to the insurance value, less the deductible provided by the law, worth 10% of the amount of damages to the livestock drowned in husbandry buildings. However, certain direct damages are not covered by the comprehensive agricultural insurance. This was the case for herds that were drowned in fields, uprooted orchard trees, operating losses, uninsurable crops and destroyed equipment. These damages were within the purview of the National Guarantee Fund for Agricultural Disasters (FNGCA in French), which was put in place by the Ministry of Agriculture and which compensated for up to 75% of damages.

39The consequences for plants and soil were linked to the combination of the duration of the flooding (between 2 and 15 days according to the areas), of the water level and of salinity levels. The impacts on the yields depended on the duration of waterlogging and on the cultivation stage; for instance, after 10 days of submersion in sweet-water, plants lost 0.6 tiller per plant and 3 grains per ear (Collaku and Harrison, 2002).

40Salinity causing the most damage, it was vital to repair the drainage system to mitigate the impacts. A campaign to analyze salinity levels was organized by the Chambers of Agriculture, with the financial support of the General Councils (Chamber of Agriculture 17, 2010). However, it was not possible to reach a sufficient level of desalination due to the weeks of adverse rainfall conditions that followed the catastrophe.

41The future and sustainability of the agricultural sector in the area was therefore at stake. For the past few years, the agricultural community has been requesting the restoration, consolidation and even the raising of dykes in order to ensure the protection of the land. Yet, the elaboration of a zoning plan following the storm raised fears among several agricultural organizations, such as the FDSEA 17 (Charente Maritime Departmental Federation of Farmers' Union), that certain seawalls would be overlooked, which would make some zones prone to flooding.

42Other than the publication of decrees for natural disasters, an outstanding action plan was announced by the Ministry of Food, Agriculture and Fisheries, and validated by the European Commission. The speed with which this agreement was reached (less than 2 months) illustrates the gravity of the situation. This compensation scheme of 20 million euros for aquaculture and 1.5 million for agriculture includes support to replace equipment (up to 75% of the reinvestment) and the implementation of the National Agricultural Disaster Guarantee Fund and the Burden Reduction Fund (outstanding loans and new loans). To this national assistance can be added regional initiatives such as the Region Storm Emergency Plan or the release of emergency funds by the concerned General Councils. Nevertheless, due to the gravity of the damages caused by Storm Xynthia, this financial support will need to be maintained on the long term to enable companies and professionals to face the impacts and recover.

Risk management, a major element for facing disasters

Exposure to risk

43Storm Xynthia had major consequences for the towns of La Faute-sur-Mer and L’Aiguillon-sur-Mer. This area is in fact somewhat familiar with phenomena of coastal flooding. The current configuration of the Bay of l’Aiguillon and its periphery is the result of successive embankments which, between the Middle Ages and the 1960s, isolated almost 100,000 hectares of the former “Gulf of Pictons” to create the Poitevin marshland (Marais Poitevin) (Verger, 2009; Fig. 5). This territory is characterized by the constant struggle to prevent marine waters from flooding the created polders, protected by a series of dykes. In less than 200 years, the landscape therefore greatly evolved, and the shorelines gained ground on the sea over 15 km. This frenzy even led to imagine insane projects like draining the Bay of l'Aiguillon and leaving only a passage for the Sèvre Niortaise River.

Former waterway
Dam with double function
Dam with single function
Main sluice gate
Formerly planned dam
Dyke
Abandoned embankment project
Envisaged closure of the bay
Shellfish farm
Date of embankment
Periphery and former islands
Barrier beach
Dunes
Dried marshland
Wet Marshland
Schorre

Channel at low water, foreshore

Main ingress of water or breaches
Waves that went over the dyke
Urban zone heavily affected by storm Xynthia (28 victims)
Flooding caused by storm Xynthia in 2010

Sources: according to F. Verger, Zones humides du littoral français, 2009; SERTIT 2010, flooding according to SPOT 4 of March 2nd 2010; CGEDD (September 16th 2010, Mission n°007336-01). Map by Andrée DUBOIS, IGARUN.

44The phenomenon of coastal flooding engendered by storm Xynthia is not anecdotal and it is reasonable to wonder if, in history, the communities living on these territories showed resilience, this term referring to the capacity of a system to maintain its functions and to reorganize itself following a shock (Bouchon, 2007), or if they were ignorant of the risks they could face living in these areas. According to the historian T. Sauzeau, “the memory of deeply rooted inhabitants, confirmed by archives, tells us that villages have always been vulnerable to flooding, but also that traditional societies were very resilient” (2010).

45Since 1738 (written evidence was found), eleven floods sufficiently severe to be historically remembered were listed (tabl. 1), an average of one every 25 years (one per generation).

Tabl. 1: marine flooding events in the northern part of the Bay of l'Aiguillon, Vendée

1738

Flooding between Saint-Michel-en-L'Herm and L'Aiguillon-sur-Mer.

1740

Storm that caused a flood up to Luçon.

1850

Tidal wave that flooded hundreds of hectares of land in L'Aiguillon-sur-Mer and Saint-Michel-en-l'Herm.

October 27th 1882

Dykes were flooded in La Faute-sur-Mer.

1906

Flooding in the northern part of La Faute-sur-Mer.

March 21st 1928

Flooding in the north of the Pointe d'Arcay in the Vieille Prise and Jeune Prise areas on 120 hectares. The village of La Faute-sur-Mer was then an island.

1930

Severe attacks from the sea that destroyed a dyke over 800 meters in La Faute-sur-Mer.

March 14th 1937

Failure of the protection dam of the hamlet of la Faute, and of the dams in l’Aiguillon-sur-Mer and Triaize.

November 16th 1940

Breach in the Wagons dam in Triaize, leading to the flooding of 3,000 ha of cultivated fields with a tidal coefficient of only 88.

December 27th 1999

Failure of the protection dam in L'Aiguillon-sur-Mer, flooding approximately 30 ha of agricultural lands with a tidal coefficient of 77.

February 28th 2010

Flooding of parts of the towns of La Faute-sur-Mer and L'Aiguillon-sur-Mer, as well as most agricultural lands in the Bay of l'Aiguillon.

Sources: Departmental archives of la Roche-sur-Yon; GARNIER and SURVILLE, 2010.

46If we only consider the floods during the 20th century, the frequency increases to one every 15 years. The phenomenon thus seems to have intensified in the 20th century, especially in the first half. State services are aware of this risk: as early as the 19th century, engineers mapped the sectors affected by marine flooding, the failure of dunes, etc. (Tenaud-Caillé, 1997). “In 1824, a letter to the Prefect of Vendée read ‘we should be concerned about equinoctial tides because these high tides, if they are accompanied by gales, can be very damaging’ (…) in 1842, the General Council of Vendée signaled that the dunes were damaged by the sea when bad weather conditions and high tides combined, and that the areas located behind them were flooded on several occasions” (Tenaud-Caillé, 1997). The town of l'Aiguillon was relocated in the 19th century and development and land-use decisions on certain wetlands and dunes provoked their subsidence, which exposed houses to a flooding from the Lay River.

47The risk in this area was therefore known. Let us note that it “implies human presence, the perception of a more or less predictable potential danger by a social group or by an individual” (Meschinet de Richemond, 2007). The increasing exposure of goods and people in the lower zones (2 to 4 m NGF) is a recent phenomenon in these coastal towns. Figures 5 and 6 illustrate the progression of urbanization in these areas of the sandy Pointe d’Arcay, which appeared in the early 17th century. Until then, the mouth of the Lay River was situated where the locality “la Belle Henriette” is now located, and the Pointe d’Arcay did not yet exist. Because the mouth of the Lay shifted towards the south-east, the reclamation of the Bay of l'Aiguillon was made possible, without, however, being able to prevent flooding (table 1). The maps in Figure 6 reveal how the urbanization of La Faute-sur-mer accelerated in the 1980s and that the most affected neighborhood did not yet exist in 2006. The most exposed areas, which are topographically low, were constructed more recently.

Coastal development with no real regulations

48To understand the extent of the human toll due to storm Xynthia, we should consider the spatial forms of urban development. The geographers from Nantes Jean Renard, Alain Chauvet and Jacques Marcadon, were already concerned about the coast of Vendée 30 years ago, on “the nature and quantity of space changing functions, and on the way these transfers of function were operating, at the expense of who or what and in favor of who or what?” (Renard, 1980). This urbanization process, which experienced a turning point in the 1970s, has four main characteristics.

Strong pressure linked to the development of beach tourism

49Vendée is the second tourist department of France in terms of accommodation capacity, with 660,000 beds in 2010, behind the Var department with 865,000 beds and before the Alpes-Maritimes with 656,000 beds (INSEE, 2010). Its seafront experienced the strongest increase of the tourist accommodation capacity in the country between 1990 and 2010, with +27.5% of the number of beds, far ahead the Alpes-Maritimes which is also very dynamic, with +23.9% (+11.7% on average for the whole French coastline). Yet, in 1968, Vendée was only the 6th French coastal department in terms of vacation homes, with 24,000 houses, whereas the Loire Atlantique was 3rd with 34,000 houses. In 2007, the Vendée was ranked 4th with 108,000 housing units and the Loire Atlantique 11th with 70,510 (INSEE, 2007).

50In the early 1970s, the coast of Vendée entered an era of massive urbanization. Housing schemes and apartment buildings were constructed by real estate companies with much more capital and financial ambitions than previous property developers. “We can observe that these operations were done by building contractors, land surveyors or accountants, traders [including real estate agents], etc... but also big promoters from Challans or Paris (SCI Merlin for instance...)” (Chauvet, 1980). Just as in la Faute-sur-Mer, these new stakeholders introduced the model of vertical integration in the process of urbanization, from land ownership to commercialization as well as construction. Coastal urbanization was scaled up.

… combined with a declining agricultural sector

51This urban development occurred to the detriment of the declining agricultural sector. The conversion of real estate was acclaimed in a number of towns. Between 1970 and 1980, the agricultural surface area used by coastal towns in Vendée decreased from 5.1% to 2.5% for the whole department, thereby illustrating an “expiring” coastal agriculture, compared to the “dominant model of high-intensity agriculture” (Renard, 1983).

52The destructuring of traditional agriculture in the Vendée coastal territories provoked a rupture in the narrow junction that existed between the shoreline of the marsh (the contact between dunes and marsh) and the swamp itself (Chauvet, 1980). Although the constructible land was limited along the dunes, the urbanization process first spread on the shore, before diffusing to the topographically low marshlands.

… and the monopolization by interest groups linked to tourism

  • 8The analysis of the municipal elections of 1977 along the coast of Vendée reveals the deep changes (...)
  • 9 Plan d'Occupation des Sols – land use plan in France.
  • 10After 1973, there were many articles in the regional press dealing with the numerous conflicts tha (...)

53Concerning local elections, the decreasing influence of rural areas has led to the transformation of the socio-professional composition of municipal councils” (Marcadon, 1980). Interest groups linked to tourism are implicated in decision making by advocating for local development8. Government services tried to curb urban extension by elaborating a Planning Scheme for the Center West Atlantic Coast (ALCOA, 1977). Conflicts appeared between the administration and local elected officials, some are provoked by environmental protection associations, others sometimes occur between local interest groups. These discords were exacerbated by the implementation of the first POS9, which represented for numerous local officials a legislative framework hard to accept10.

… in a context of timid regulation, often exonerated from constraints of urban development

54Numerous municipalities were reluctant to adopt a POS, as they thought it limited the possibilities of construction; there were numerous fits of anger from officials who associated it to administrative hassle. Some officials even spoke of “an act of force by the Administration”, of administrative pressure against the will of 'elected officials'” and of “an authoritarian and insidious act” (Renard, 1980).

55After this phase of hesitation, the first documents were approved and greatly distributed construction licenses across the territory. Previous works have compared the extent of urban-oriented areas in these first coastal POS with that of inland towns with identical populations, surface areas and urban pressure: these urban-oriented areas in coastal POS often offered “...a ratio of surface areas... of 1 to 10…” (Renard, 1980, Pottier, 1987). In the early 1980s, in the first 33 coastal POS in Vendée, 13,000 hectares were dedicated to urbanization, three thirds of which were located outside existing urban fabric (Renard, 1983).

  • 11 The touristic golden calf is coveted and it's not possible to have one's neighbor in zone NA, when (...)

56We saw that the high demand was not hampered by agriculture in the competition for land. If agriculture had better resisted, the process would have been different because of this competition for land and of a development model more based on the local. This was the case in Noirmoutier with early potatoes grown on the coast, or with the vineyards in Nantes, where these very profitable types of agriculture opposed total urbanization. Conversely, social evolutions were all marked by the seizing of local powers by stakeholders who were clearly interested in residential touristic development. Farmers were in the majority in municipal councils, but their influence rapidly declined, as their place in society diminished. There were less and less farmers and other professions had another idea of society. Over 30 years ago, academic institutions in Nantes were already condemning the land speculation that provoked the loss of land and of sensitive natural areas for the sole benefit of urbanization11.

57In Vendée, the coast is made up of long stretches of sand dunes often planted with forests of maritime pines and which isolate numerous marshes and coastal wetlands. It was soon saturated with constructions in the best locations, often near the sea: “In l'Aiguillon-sur-mer, settlements on the dunes took a similar turn than in La Faute-sur-Mer. Where the band of dunes swells the most, two urban neighborhoods flourished, along the road that follows the dune ridges” (Tessier, 1984). This phenomenon can be observed on the French IGN maps in figure 6.

58From 1959 to 2006, the forests on dunes, the shores of marshes and wetlands succumbed to residential development. This happened at the risk of degrading of the environment. The vulnerability of these towns is linked to the difficulty of adopting a regulation instrument that takes into account geographical configurations and sensitive sectors. Yet, the State tried relatively early on to avoid constructing on the seaside, not only to protect remarkable sites along the coast, but also to limit the risks: “Outside urban areas, constructions or installations are forbidden within a 100 meters wide coastal strip between the high tide shoreline or the highest water mark for inland bodies of water... The local land use plan can claim a higher distance if the fragility of certain ecosystems or if coastal erosion can justify it” (Article L146 from the law of January 3rd 1986).

The evident lack of a risk culture

59The vulnerability of this zone to the risk of flooding reveals how unsuitable general preventive measures are. The government developed restrictive preventive tools, through the Plans for Flood Risk Prevention (PPRI in French), which have been the most structuring and operational instruments for the past 15 years. And yet, out of the 864 coastal towns in the country exposed to marine flooding, barely 5% of them had an approved PPRI when Xynthia hit the continent. In the zone which concerns us, the PPRI of the Lay estuary had been subject to a prefectoral order dating from June 7th 2007 for early application in the towns of la Faute-sur-Mer and l’Aiguillon-sur-Mer. However, its implementation was complicated: “the municipal council of La Faute-sur-Mer decided on November 10th 2009, by unanimous vote (13 officials out of 15), to request a three months delay for the public enquiry concerning the PPRI. This public enquiry is essential to ensure the long-term implementation of the PPRI, which is designed to curb urbanization in the town” (Libération, Monday 8th of March 2010, p. 14). Moreover, the town in question did not adopt the local emergency action plan (PCS in French), mandatory since the law of August 13th 2014. The issue of the responsibilities of elected officials is therefore at stake.

60Despite 15 years of experimentations, these delays illustrate the difficulty to engage a dialogue between state services, who are at the initiative of their establishment, local elected officials, who often try to extend constructible land along the coast by using the time factor, poorly informed inhabitants who contribute to this general pressure, and land developers who contribute as much. The Plans for Flood Risk Prevention are more generally associated to risks of flooding (river towns) rather than to marine submersion or flooding, as they are based on property damage rather than on human toll. “These characteristics show the necessary adaptability of this type of plan to coastal towns. This might justify why these towns are not interested and block this type of plan” (Anziani et al., 2010).

61The Plan for Flood Risk Prevention for la Faute-sur-Mer was approved on June 8th 2007. It defined the blue zones for property development and the red unbuildable zones. This zoning did not take micro-topography considerations into account. The low areas between 2 and 3 meters NGF behind the dyke along the Lay River, and the wetlands along the small coastal river at the same altitude, were buildable. In the PPRI, the only constraint was the size of the construction in comparison to the total surface area of the land plot, what is referred to as the Floor area ratio (COS in French). Other than this, no architectural restriction, such as crawl spaces or survival rooms in the upper floor as specified in other PPRI (towns of Jousseaume and Mercier, 2009), were mentioned in the PPRI of towns in Vendée, even though the main housing styles are single floor houses. The type of houses built in flood-prone areas constitute the most aggravating factor for the survival of populations. No house is affected by the flood risk if its living rooms are elevated, and yet there is no house on stilts. However, since the storm, the Vendée Prefecture imposed, via the decree of August 9th 2010, the establishment of a new Plan for Flood Risk Prevention for the Lay estuary that takes into consideration the consequences of storm Xynthia. The reference sea level is 5.7 meters NGF; this corresponds to the 4.7 m NGF maximum sea level during Xynthia, plus a meter to take into account the foreseeable effects of climate change on sea level rise, as required by the interministerial circular dating from April 7th 2010. Nonetheless, this ordained level is not based on a proper study. Moreover, in the new plan, the creation of a threshold level has become the norm for all zones concerned by the plan.

62These recurrent elements illustrate the lack of a shared risk culture. In fact, this term has only started to be used by politicians, which highlights how France lags behind in this respect compared to other European countries. This is stressed by Dubois-Maury and Chaline (2004), who believe risk culture can only be developed through a series of reasoned procedures that imply: (1) informing all populations liable of being subjected to risk of the behaviors to adopt in case of emergency, from survival reflexes to confinement and evacuation; (2) preparedness drills, based on potential scenarios, already done in certain cities; (3) a specific effort for risk preparedness addressed to identifiable “key members” in the community (p. 188). Although risk prevention is enshrined in the legislation, its efficiency should be reconsidered. Policies of flood risk prevention in France nowadays are too much based on zoning (De Vanssay, 2004; Scarwell and Laganier, 2004). The efforts to raise awareness among the exposed populations constitute a weak spot in these measures. Yet, numerous studies have demonstrated the efficiency of psychological and mental preparation of exposed populations (Weichselgartner, 2004; De Vanssay, 2004; Ruin, 2009).

63Moreover, the problem is exacerbated in areas characterized by the low frequency of natural disasters, which is the case for most territories in France, including the coastal towns affected by storm surges during Xynthia. It is hoped that the populations in French south-eastern regions exposed to flash floods remain vigilant due to the high incidence of these intense hazards; but how can this be ensured in regions where this occurrence is 10 to 20 times lower?

Conclusion

64During the post-crisis management, which was still ongoing as this article was being written, numerous factors came to illustrate the inconsistency of the announcements made to the populations by public authorities. During this phase, which started in April 2010 and continued until the end of the same year, the contradictory decisions made by the government throughout the months (creation, modification and reduction of “black zones”) crystallized states of mind. People affected by the storm organized themselves into associations to first soften the implementation of radical decisions. The legitimacy of “black zones”, which were very quickly renamed “solidarity zones” due to the pressure, was contested. The extreme rapidity with which they had been delineated made them quite questionable; this led to complementary evaluations between June and July 2010. In Vendée, out of 823 plots of land rapidly delineated, 508 of them had been sold by the owners and repurchased by the government by August 30th 2010. Legal battles were just beginning. At the end of April, the Vendée Prefect was ordered by the administrative tribunal, at the request of the Vendée Flood Victims Association in expedited proceedings, to provide the documents relating to the conditions of elaboration of “black zones”. Certain victims whose houses were located in “black zones” started repair works.

65This post-disaster management is so far very damaging on the long term, as it weakens the climate of trust vital for developing risk culture in our country. Moreover, the achievement of a risk culture implies that all stakeholders associated to the disaster question their own responsibility. Until certain politicians were taken in custody almost 14 months after storm Xynthia, the State seemed to have been designated as responsible for the disaster, the responsibility of several local officials having been concealed until then. Moreover, scientists need to improve their forecasts and simplify their messages. The acknowledgement of the various responsibilities is one of the keys to learn from the decisions taken at a local level.

66On another temporal scale, storm Xynthia and its repercussions reveal the weak awareness of risks in vulnerable territories and the degree of collective irresponsibility. Previous generations were less bereft in this sense. Much awareness-raising and dialogue is thereby still needed.

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Bibliografía

ANZIANI A. et al., 2010, Rapport d'information sur les conséquences de la tempête Xynthia, 554, 10 juin, 100 p.

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GARNIER E., SURVILLE F. (dir.), 2010, La tempête Xynthia face à l’histoire. Submersions et tsunamis sur les littoraux français du Moyen-Age à nos jours, Le Croît Vif, Saintes, 174 p.

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See also :

Archives départementales numérisées de la Vendée, http://archives.vendee.fr/

Blog de l'ancien maire de Longeville-sur-Mer, passionné par l'histoire de l'Ile de la Dive, http://ladive85.canalblog.com/

http://www.littoral.ifen.fr/fileadmin/user_upload/lettres/capacite.pdf

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Notas

1 Monthly weather report, February 2010, Charente-Maritime, n°62, 4 p: atmospheric pressure at sea level in La Rochelle (Laleu Airport)

2 http://france.meteofrance.com/france/actu/actu?portlet_id=50150&­document_id=22­089

3 http://france.meteofrance.com/france/actu/actu?portlet_id=50150&­document_id=22­089

4 NGF (Nivellement Général de la France) corresponds to the Ordnance Datum Newlyn in the British Isles.

5 Longlines are used for offshore farming. They are composed of two moorings with a cable in between to support cages or tanks, both shellfish farming props.

6 http://www.cnc-france.com/index.php?rub=2

7 Example of the Prefectoral order n°2010-5366 dating from May 12th 2010 by the Prefecture of Charente Maritime.

8The analysis of the municipal elections of 1977 along the coast of Vendée reveals the deep changes that the region has undergone in 25 years. In 1953 and 1959, there were mainly farmers living in the coastal towns and fisheries professionals were living in ports; in 1971 and especially 1977, they gave way to traders, craftsmen, liberal professionals and senior executives and middle managers and employees also appeared...” J. Renard, 1980, p. 16.

The socioprofessional composition of the current Council illustrates the extent to which the influence of farmers (there are only 5 of them left) and of fishermen (only 2) has been declining...”, A. Chauvet, 1980, p. 59.

9 Plan d'Occupation des Sols – land use plan in France.

10After 1973, there were many articles in the regional press dealing with the numerous conflicts that erupted in Yeu island, Noirmoutier, Longeville or Château d’Olonne, conflicts that were based on the construction licenses determined by the POS”, Renard, 1980, pp 14.

11 The touristic golden calf is coveted and it's not possible to have one's neighbor in zone NA, when we are in zone NC ourselves!” (Marcadon, 1980, pp. 82) [zones NA and NC are both natural zones according to urban planning legislation in France]. “What is even more indicative of the power relations and issues at stake is the social composition of the elected officials participating in working groups on POS. Besides mayors, for the sake of experience but also of interests, there are notaries, real estate agents, masonry contractors, land owners and traders who sit in these committees and who make decisions that will steer town policies... (…) Such a choice only substantiates the need for tourism” (Renard, 1980, pp. 17). “For over 20 years, we observe that the Administration and the rare officials who want to organize or curb the use of land for touristic purposes are regularly overshadowed by certain irrevocable situations” (Renard, 1983, pp. 179).

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Título Fig. 4: location of shellfish farms in the l'Aiguillon area
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Leyenda Former waterway Dam with double function Dam with single function Main sluice gate Formerly planned dam Dyke Abandoned embankment project Envisaged closure of the bay Shellfish farm Date of embankment Periphery and former islands Barrier beach Dunes Dried marshland Wet Marshland Schorre Channel at low water, foreshore Main ingress of water or breaches Waves that went over the dyke Urban zone heavily affected by storm Xynthia (28 victims) Flooding caused by storm Xynthia in 2010
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Para citar este artículo

Referencia electrónica

Etienne Chauveau, Céline Chadenas, Bruno Comentale, Patrick Pottier, Amandine Blanlœil, Thierry Feuillet, Denis Mercier, Laurent Pourinet, Nicolas Rollo, Ion Tillier y Brice Trouillet, « Xynthia: lessons learned from a catastrophe », Cybergeo : European Journal of Geography [En línea], Medio ambiente, Naturaleza, Paisaje, documento 538, Publicado el 11 abril 2017, consultado el 25 mayo 2017. URL : http://cybergeo.revues.org/28032 ; DOI : 10.4000/cybergeo.28032

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Autores

Etienne Chauveau

Géographe, Université de Nantes, Géolittomer LETG UMR 6554 CNRS, France
etienne.chauveau@univ-nantes.fr

Céline Chadenas

Géographe, Université de Nantes, Géolittomer LETG UMR 6554 CNRS, France
celine.chadenas@univ-nantes.fr

Bruno Comentale

Géographe, Université de Nantes, Géolittomer LETG UMR 6554 CNRS, France
bruno.comentale@univ-nantes.fr

Patrick Pottier

Géographe, Université de Nantes, Géolittomer LETG UMR 6554 CNRS, France
patrick.pottier@univ-nantes.fr

Amandine Blanlœil

Etudiante en Master 2 de Géographie, Université de Nantes, France
amandine.blanloeil@univ-nantes.fr

Thierry Feuillet

Géographe, Université de Nantes, Géolittomer LETG UMR 6554 CNRS, France
thierry.feuillet@univ-paris4.fr

Denis Mercier

Géographe, Université de Nantes, Géolittomer LETG UMR 6554 CNRS, France
denis.mercier@univ-nantes.fr

Laurent Pourinet

Géographe, Université de Nantes, Géolittomer LETG UMR 6554 CNRS, France
laurent.pourinet@univ-nantes.fr

Artículos del mismo autor

Nicolas Rollo

Géographe, Université de Nantes, Géolittomer LETG UMR 6554 CNRS, France
nicolas.rollo@univ-nantes.fr

Ion Tillier

Géographe, Université de Nantes, Géolittomer LETG UMR 6554 CNRS, France
ion.tillier@univ-nantes.fr

Brice Trouillet

Géographe, Université de Nantes, Géolittomer LETG UMR 6554 CNRS, France
brice.trouillet@univ-nantes.fr

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Derechos de autor

© CNRS-UMR Géographie-cités 8504

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