Radar rainfall measurement:: << hydrologic visibility >> in mountainous regions

This paper presents a simulation procedure aimed at the predetermination of the hydrological quality that a given weather radar may obtain over a given region in space, typically a hydrologic catchment. First, the influence of three error sources (ground clutter, shadows and effects linked to vertical structure of the atmosphere) is modelled in terms of error on the rain-rate. This modelling relies on the knowledge of the relief and of a climatology of the vertical structure of rain, only. Then, a rainfall-runoff simulation is performed over the catchment of interest. Given reference areal rainfall time series, the radar error simulation procedure is used to generate radar rainfall space-time series. The hydrological impact of the radar errors, and of various radar data processing techniques, can then be evaluated in terms of discharge at the catchment outlet with a distributed hydrologic model (TOPODYN). A case study, devoted to analyse the coverage of the Ardeche basin by the two weather radars operated by Meteo France in Nimes and Bollene, is presented.