Evaluation of multiple downscaling tools for simulating extreme precipitation events over Southeastern South America: a case study approach

A collection of 10 high-impact extreme precipitation events occurring in Southeastern South America during the warm season has been analyzed using statistical (ESD) and dynamical downscaling approaches. Regional Climate Models from the CORDEX database for the South American domain at two horizontal resolutions, 50 km and 25 km, short-term simulations at 20 km and at 4 km convective-permitting resolution and statistical downscaling techniques based on the analogue method and the generalized linear model approach were evaluated. The analysis includes observational datasets based on gridded data, station data and satellite products that allow assessing the observational uncertainty that characterizes extreme events in the region. It is found that the ability of the modelling strategies in capturing the main features of the extreme rainfall varies across the events. The higher the horizontal resolution of the models, the more intense and localized the core of the rainfall event, being the location of the exit region of the low-level jet and the low-level moisture flux convergence during the initial stages of the events the most relevant features that determine models’ ability of capturing the location and intensity of the core of the heavy rainfall. ESD models based on the generalized linear approach overestimate the spatial extension of the events and underestimate the intensity of the local maxima. Weather-like convective-permitting simulations depict an overall good performance in reproducing both the rainfall patterns and the triggering mechanisms of the extreme events as expected, given that these simulations are strongly controlled by the initial conditions.