Error model for radar quantitative precipitation estimates in a Mediterranean mountainous context

Characterizing the error structure of radar quantitative precipitation estimation (QPE) is recognized as a major issue for applications of radar technology in hydrological modelling. This topic is further investigated in the context of the Cevennes-Vivarais Mediterranean Hydrometeorological Observatory dedicated to improving observation and modelling of extreme hydrometeorological events in the Mediterranean. The reference rainfall problem is firstly addressed: after quality-control of the raingauge measurements, various interpolation techniques (isotropic and anisotropic Ordinary Kriging, Universal Kriging with external drift) are implemented and compared through a cross-validation procedure. Then, the block Kriging technique allows the estimation and selection of reference values for a series of time-steps (1-12 h) and hydrological mesh sizes (5-50 km(2)). The conditional distributions of the residuals between radar and reference values are modelled using generalized additive models for location scale and shape. The distributions are analysed for the operational real-time radar products and the Observatory re-analysed products, the latter being by construction less affected by conditional bias. As expected, the error model is dependent on the space and time scales considered. The hourly raingauge network is found to be not dense enough for providing reliable spatial estimations for sub-daily time-steps.