Time series analysis and cross-wavelet analysis are used to characterize the relationship between water input and displacement in the most active zone of the Séchilienne unstable slope. Time series analysis shows a displacement long term trend and seasonal intra-annual variations, respectively independent and synchronous to precipitations. Wavelet analysis has allowed identifying and characterizing the precipitation-detrended displacement relationship which shows that the Séchilienne destabilisation is rather linked to effective rainfall than to raw precipitation (rainfall + snowfall), involving then groundwater process. Seasonal analysis of this relationship was performed, showing that displacement rate follows the behaviour of the hydrological cycle. Finally, trend was analysed and a weakening model approach was developed with an attempt to forecast the next modifications in unstable slope destabilisation behaviour.