Probabilistic quantitative precipitation forecast calibration over South America: Experiments with a short range regional ensemble

Different techniques for obtaining probabilistic quantitative precipitation forecasts (PQPFs) over South America are tested during the 2002-2003 warm season. Some of the techniques are based on a parametric representation of the conditional probability of precipitation over a particular threshold given a certain value of forecasted precipitation and the other uses a non-parametric estimation of the probabilities. The results are also compared with the calibration algorithm based on the rank histogram. A number of experiments were performed to compute a reasonable size for the training period.

The PQPFs of a short range ensemble forecast system (SREF) based on the WRF model and the breeding technique were calibrated using the different approaches and the resulting PQPFs scores were compared.

The calibration is performed using two different data sets, one derived from a high resolution rain gauge network and the other one based on passive microwave satellite estimates. This is done in order to evaluate if the use of satellite derived rainfall produces a significant degradation of PQPFs reliability and resolution.