Les réseaux routiers sont fréquemment affectés par des aléas naturels, entraînant des coupures et, parfois, des situations d’isolement territorial aux conséquences directes et indirectes variées. Les réseaux peu denses ou de configuration arborescente, caractéristiques des zones montagneuses, limitent les itinéraires alternatifs et accentuent ainsi le risque d’isolement. La perte d’accessibilité territoriale représente un enjeu majeur, avec des répercussions indirectes sur le fonctionnement des sociétés. Cependant, la question spécifique de la rupture d’accessibilité territoriale liée aux avalanches demeure peu étudiée. Les travaux existants adoptent généralement une approche statique, omettant de considérer l’ensemble des caractéristiques démographiques des territoires. Ces facteurs, pourtant essentiels, évoluent rapidement sous l’effet du changement climatique, qui modifie à la fois la fréquence et l’intensité des aléas naturels et participe à l’évolution des dynamiques démographiques. Cette étude propose une lecture temporelle du risque d’isolement territorial. Elle repose sur une quantification diachronique de la vulnérabilité des réseaux routiers, permettant de caractériser l’évolution du risque à travers des indicateurs spatialisés. La méthodologie s’appuie sur le calcul d’indices qui associent un indice d’exposition à des données démographiques. L’objectif est d’obtenir un indice de risque d’isolement territorial prenant en compte la dynamique des aléas et des territoires. L’application de cette méthode au département des Alpes-Maritimes entre 2003 et 2023, pour l’aléa avalanche, révèle une concentration du risque d’isolement territorial sur un nombre limité de tronçons routiers. Plusieurs tronçons routiers desservant des pôles isolables présentent des niveaux d’exposition élevés, mais le risque se concentre principalement sur l’accès à la station d’Isola 2000, où se combinent une forte exposition aux avalanches et une population desservie importante. Par ailleurs, si le niveau de risque de ce tronçon fluctue au cours de la période étudiée, aucune diminution significative n’est observée depuis 2003. Cette approche met en lumière l’intérêt opérationnel de combiner indices d’exposition et données démographiques avec une approche temporellement dynamique pour analyser les modifications du risque d’isolement territorial.
Road networks are frequently affected by natural hazards, resulting in disruptions and, in some cases, situations of territorial isolation with a range of direct and indirect consequences. Sparse or tree-like road networks, which are characteristic of mountainous areas, limit alternative routes and thereby increase the risk of isolation. The loss of territorial accessibility represents a major challenge, with indirect impacts on the functioning of societies. However, the specific issue of disrupted territorial accessibility related to avalanches remains poorly studied. Existing studies generally adopt a static approach, overlooking the full range of demographic characteristics of territories. These factors, however, are essential and are rapidly changing under the influence of climate change, which alters both the frequency and intensity of natural hazards and contributes to changes in demographic dynamics. This study proposes a temporal analysis of the risk of territorial isolation. It is based on a diachronic quantification of road network vulnerability, enabling the characterization of risk evolution through spatially explicit indicators. The methodology is based on the calculation of indices that combine an exposure index with demographic data. The objective is to develop a territorial isolation risk index that accounts for the dynamics of both hazards and territories. Application of this method to the Alpes-Maritimes department between 2003 and 2023, for avalanche hazards, reveals a concentration of territorial isolation risk on a limited number of road segments. Several road segments providing access to potentially isolated population centres exhibit high exposure levels, but the risk is primarily concentrated on the access route to the Isola 2000 ski resort, where high avalanche exposure combines with a large served population. Furthermore, although the risk level of this road segment fluctuates over the study period, no significant decrease has been observed since 2003. This approach highlights the operational value of combining exposure indices and demographic data with a temporally dynamic approach to analyse changes in territorial isolation risk.
This article contributes to document glacier retreat in several areas of three massifs of the French Alps (Mont-Blanc, Vanoise and Écrins) over the last century, a process that has accelerated significantly in recent decades due to the climate crisis. The study is based on a comparison between 12 panoramic photographs by the French geodesist Paul Helbronner (1871-1938), taken between 1905 and 1920 during the measurement campaigns that formed the basis of his Description géométrique détaillée des Alpes françaises (Detailed geometric description of the French Alps), and recent aerial images (2022-2023). It enables the quantification of glacier area loss and the morphological transformation of glacier systems. Monoplotting, applied to three glaciers, accompanied the use of a geographic information system for all the glaciers. These two methods made it possible to reconstruct glacier outlines and to propose a typology of ice bodies (202 entities). 48,5 % of the features studied have disappeared, with variations depending on their size and morphology: 82 % of ice-snow fillings in couloirs and 29 % of ice aprons have disappeared, whilst valley, slope and cirque-and-slope glaciers have retreated to a lesser extent despite their significant fragmentation. This glacier retreat is also accompanied by the formation of new lakes, which are also documented. The study highlights the scientific and heritage value of Helbronner’s photographs for the diachronic analysis of high-mountain landscapes and emphasises the relevance of using them for the long-term monitoring of deglaciation and the anticipation of future environmental impacts.
This article contributes to document glacier retreat in several areas of three massifs of the French Alps (Mont-Blanc, Vanoise and Écrins) over the last century, a process that has accelerated significantly in recent decades due to the climate crisis. The study is based on a comparison between 12 panoramic photographs by the French geodesist Paul Helbronner (1871-1938), taken between 1905 and 1920 during the measurement campaigns that formed the basis of his Description géométrique détaillée des Alpes françaises (Detailed geometric description of the French Alps), and recent aerial images (2022-2023). It enables the quantification of glacier area loss and the morphological transformation of glacier systems. Monoplotting (photogrammetric technique that requires only a single image and a digital elevation model), applied to three glaciers, accompanied the use of a geographic information system for all the glaciers. These two methods made it possible to reconstruct glacier outlines and to propose a typology of ice bodies (202 entities). 48,5% of the features studied have disappeared, with variations depending on their size and morphology: 82% of ice-snow fillings in couloirs and 29% of ice aprons have disappeared, whilst valley, slope and cirque-and-slope glaciers have retreated to a lesser extent despite their significant fragmentation. This glacier retreat is also accompanied by the formation of new lakes, which are also documented. The study highlights the scientific and heritage value of Helbronner’s photographs for the diachronic analysis of high-mountain landscapes and emphasises the relevance of using them for the long-term monitoring of deglaciation and the anticipation of future environmental impacts.
