Intensity–duration–frequency (IDF) rainfall curves in Senegal

Urbanization resulting from a sharply increasing demographic pressure and the development of infrastructures have made the populations of many tropical areas more vulnerable to extreme rainfall hazards. Characterizing extreme rainfall distribution in a coherent way in space and time is thus becoming an overarching need that requires using appropriate models of IDF curves. Using 14 series of 5-min rainfall records (aggregated at a basis time-step of 1 h) collected in Senegal, a comparison of two GEV&scaling models is carried out, leading to adopt the most parsimonious one, built around four parameters. A bootstrap approach is proposed to compute the uncertainty associated with the estimation of these 4 parameters and of the related rainfall return levels for durations ranging from 1 h to 24 h. This study confirms previous works showing that simple scaling holds for characterizing the time-space structure of extreme rainfall in tropical regions such as sub-Saharan Africa. It further provides confidence intervals for the parameter estimates, and shows that the uncertainty linked to the estimation of the GEV parameters, is 3 to 4 times larger than the uncertainty linked to the inference of the scaling parameter. From this model, maps of IDF parameters over Senegal are produced, providing a spatial vision of their organization over the country, with a North to South gradient for the location and scale parameters of the GEV. An influence of the distance from the ocean was found for the scaling parameter. It is acknowledged in conclusion that climate change renders the inference of IDF curves sensitive to increasing non stationarity effects, requiring to warn end-users that they should be used with care and discernment.