A statistical–topographic model using an omnidirectional parameterization of the relief for mapping orographic rainfall

The knowledge of rainfall patterns is a key issue for regionalization in hydroclimatic studies. In mountainous areas, the sparsity of the measurement network and the complexity of relationships between rainfall and topography make an accurate and reliable spatialization of rainfall amounts at the regional scale difficult. The purpose of this paper is to present an objective, analytical and automatic model of quantification and mapping of orographic rainfall applied to the north‐eastern part of France but also applicable in other complex terrain. PLUVIA distributes point measurements of monthly, annual and climatological rainfall to regularly spaced grid cells through a multiple regression analysis of rainfall versus morpho‐topographic parameters derived from a digital elevation model. The use of an omnidirectional parameterization of the topography induced by a windowing technique allows better account to be taken of the synoptic‐scale weather systems generating the different rainfall quantities of interest and the spatial scale of orographic effects. It also provides a more physical interpretation of geographical and topographical parameters selected for spatial estimation. The application relies on a network of more than 150 rain gauges spread over 30 000 km2 and concerns monthly to several yearly amounts of a sequence of 20 years. Advantages and limitations of the PLUVIA system are compared with those of two commonly used methods of multi‐variate geostatistics: kriging with external drift and extended collocated co‐kriging. Copyright © 2002 Royal Meteorological Society.