Land Planning and Extreme Snow Events: The Case of Buthier Avalanche in Aosta Valley - IT

It is well known that climate change affects all sectors of human life also increasing the natural hazard. More sensitive to its effects, the Alpine regions are coped with unpredictable scenarios caused by unexpected weather conditions. The risk management is carried out by different defence methods - from the infrastructures to the management – and nowadays, it must take into account necessarily the variability of weather conditions caused by climate change. The article reports the example of the indispensable update of hazard mapping used to reduce the snow avalanche danger with urban constraints in Cogne – Aosta Valley, in north-eastern of Italian Alps. On 15th December 2008, an event induced by extreme weather and snow conditions occurred exceeding the known limits of the avalanche basin: the paper shows how the Avalanche Warning Service of Aosta Valley had to investigate in order to estimate the return period of the event and to update hazard maps. Due to the lack of information, the study was carried out coupling the historical and dendrochronological investigations of the woods embodied in avalanche basin and destroyed by the event. Thanks to the lucky presence of forests with the same age and local tree-rings surveys, the return period of the avalanche of 15th December 2008 was estimated equal to a century.