Assessing high‐resolution numerical models and bottom‐boundary factors for a Mediterranean heavy precipitation event

Abstract Topographically complex Mediterranean Spain faces significant exposure to flash flooding, particularly during late summer and early autumn, when heavy precipitation events (HPEs) are most frequent. This research focuses on the October 22–23, 2019 HPE in Catalonia (northeastern Spain), which resulted in the catastrophic flash flood of the Francolí River basin. First, the episode is examined through a series of numerical tools, testing the capabilities of state‐of‐the‐art high‐resolution models. Numerical weather prediction (NWP) model validation includes pointwise statistical indices, but also hydrological simulations as an advanced verification tool. From this verification strategy, the optimal atmospheric simulation is selected. Next, based on this simulation, the roles of two well‐known crucial bottom‐boundary factors enhancing and driving precipitation in the region (i.e., sea‐surface temperature and topography) are assessed for this event via a series of sensitivity experiments. Numerical weather simulations are generated using the Weather Research and Forecasting and Triangle‐based Regional Atmospheric mesoscale models with a variety of physical schemes, horizontal resolutions, and initial/lateral conditions. Hydrological simulations employ the Kinematic Local Excess Model, calibrated previously via radar‐derived rainfall estimates. Results show that all atmospheric simulations reproduce the general features of the flash‐flood‐producing HPE over the catchment. However, even slight changes in the model configurations lead to different runoffs and widespread statistical performance against observational data. Consequently, while current NWP models can reproduce the main features of this kind of event effectively, the accurate simulation of such events in medium‐sized basins remains an ongoing challenge. Finally, sea‐surface temperature and the complex terrain are instrumental—as in many other cases in the region—for the development of the catastrophic HPE.