An unusual Rain-on-Snow event preconditioning the catastrophic fate of the village La Bérarde, French Alps, June 2024

On June 21st, 2024, the iconic village of La Bérarde, in the centre of the massif Les Ecrins, French Alps, was destroyed by the mountain stream “Les Etancons”, that flooded the houses  and deposited more than 200,000 m³ of raw material. This catastrophic event was caused by the concomitance of rapid warming with a heavy rain on top of a snowpack unusually thick in a glaciated watershed ranging from 1700 m to 4000 m a.s.l. during which a glacial lake drained simultaneously. Using observations (in-situ and remotely sensed) and the Météo-France modelling chain S2M, reanalysing meteorological and snow conditions in mountainous areas, we  characterize a posteriori this rain-on-snow event and evaluate its contribution to the flood as well as its genuine nature within the last 65 years. Change in precipitation extremes was estimated by fitting a time dependent Generalized Extreme Value model within a Bayesian framework on available data. This analysis suggests an intensification of extreme precipitation in the studied  high alpine region which is undergoing profound landscape changes with permafrost thawing and glacial retreat leading to favorable conditions for the formation of glacial lakes. This concomitance of intense meteorological events within a rapidly changing landscape is a striking reminder of how climate change is reshaping flood risk in high alpine regions.