Relationships between landslide triggering, synoptic meteorological weather configurations and air-mass types

Remaître, A., Malet, J.-P.
Institut de Physique du Globe de Strasbourg, CNRS UMR 7516, Université de Strasbourg, 5 rue Descartes, F-67084 Strasbourg Cedex

The objective of this work is to analyze relationships between landslide events, synoptic meteorological weather configurations and air-mass types. The analysis has been performed in the Barcelonnette Basin, in the South French Alps, where an important database on landslide events is available with more than 400 events in the last two centuries. The rainfall data have been recorded in six meteorological stations ; these stations started at the beginning of the 20th century, but most of them started around the 1950’s. Principally, data are available for 24h-periods and only a small amount of new installed stations include automated recording with 6-minute data. A detailed study has been performed for 120 landslide events where the exact date of triggering is available in the database.
The statistical relationships between the rainfall and weather conditions and the type of landslides show a clear distinction for slow- and fast-moving landslides. Two main rainfall conditions can be clearly distinguished : i) persistent rainstorms with low intensities during long periods causing the saturation of the soils and ii) short rainfall events with high intensities that occur in summer.
Seventy percent of the air-mass type associated to slow-moving landslides are polar air-mass penetrating through the Atlantic Ocean or the North Sea ; these air-masses are usually cold resulting in low capacity of atmospheric moisture and moderate event rain amounts. Tropical air-masses penetrating through the Atlantic Ocean or the Mediterranean Sea exhibit high atmospheric moisture and heavy event rain amounts. This air-mass type is mainly associated to the triggering of fast-moving landslides.