A Continental Stochastic Precipitation Generator

AXA proposes a novel continental-scale generator of synthetic gridded rainfall daily timeseries (10km resolution) with applications to cross-country risk assessment under current and future climate scenarios. Europe serves as a case-study to demonstrate and assess its performance in terms of hazard modelling and extrapolation to unobserved extreme local and regional events. This generator belongs to the class of time and space reshuffling Stochastic Weather Generators (SWGs) and generates unobserved events by re-sequencing historical multisite timeseries (E-OBS). Consistency at continental scale is ensured by relying on weather regimes and atmospheric situations characterized from the ERA5 reanalysis over Europe. The use of atmospheric drivers and dry-wet alternating cycles allows for the determination of both precipitation-prone situations or on the contrary drier spells, while preserving the physics of the atmospheric water cycle. Spatial reshuffling is introduced by regional differentiation. Transitions between regimes can be either calibrated from the historical data or extrapolated to represent future states of the climate along with an appropriate uplifting of the humidity-related variables. This generator is operationally used at AXA as part of a European flood risk model and serves as the main input to an hydrological and hydraulic model.