Probabilistic Forecasts of Cyclone-induced Hazards within SPICY Project

The SPICy project aims at tackling the issue of cyclonic coastal and inland floods forecast in the French Overseas. Reunion Island, located in the tropical south-west Indian Ocean, is exposed to cyclone-induced hazards such as devastating winds, torrential rain, marine and river inundations. It is a quite small steep volcanic island with a complex orography. Therefore, the potential coastal impact is tightly related to the track and the intensity evolution of the tropical cyclone transiting nearby. Although tropical cyclone (TC) track and intensity forecast have been steadily improving for the last decades, a great amount of uncertainty remains. Risk managers or public agencies need both a reliable forecast of the TC evolution and induced impacts and an estimation of the forecast uncertainty.

Within the project, Meteo-France in Reunion Island has developed an original method to generate ensemble scenarios around RSMC’s official track forecast. The method allows modulating both tracks and intensity of the cyclone. A distinct probability is attributed to each scenario.

Given this ensemble of meteorological forecast, wind and pressure fields are generated through meso-scale modeling (Meso-NH model) for each individual scenario using a bogusing method. This high resolution ensemble of wind field can finally be used for (1) generating probabilistic products such as chance of exceeding different wind threshold (2) forcing a wave or/and storm surge model and produce probabilistic forecast of oceanic and coastal conditions.

The proposed presentation will present the ensemble generation method and provide some validation results. The tool will be illustrated through historical events.

This work is supported by the French National Research Agency (ANR – 14 – CE03 – 0013). More details on the project are available at http://spicy.brgm.fr.