ABSTRACT This study simulates an unusual extreme rainfall event that occurred in Salvador city, Bahia, Brazil, on December 9, 2017, which was named subtropical storm Guará and had precipitation of approximately 24 mm within less than 1 h. Numerical simulations were conducted using the Weather Research and Forecasting (WRF) model over three domains with horizontal resolutions of 9, 3, and 1 km. Different combinations of seven microphysics, three cumulus, and three planetary boundary layer schemes were evaluated based on their ability to simulate the hourly precipitation during this rainfall event. Statistical indices (MB = -0.69; RMSE = 4.11; MAGE = 1.74; r = 0.55; IOA = 0.66; FAC2 = 0.58) and time series plots showed that the most suitable configurations for this weather event were the Mellor-Yamada-Janjić, Grell-Freitas, and Lin formulations for the planetary boundary layer, cumulus, and microphysics schemes, respectively. The results were compared with the data measured at meteorological stations located in Salvador city. The WRF model simulated well the arrival and occurrence of this extreme weather event in a tropical and coastal region, considering that the region already has intense convective characteristics and is constantly influenced by sea breezes, which could interfere in the model results and compromise the performance of the simulations.
RESUMEN El presente estudio simula un evento inusual de lluvia extrema ocurrido en la ciudad de Salvador, Bahía, Brasil, el 9 de diciembre de 2017, que se denominó tormenta subtropical Guará y tuvo una precipitación de aproximadamente 24 mm en menos de 1 h. Se realizaron simulaciones numéricas utilizando el modelo Weather Research and Forecasting (WRF) en tres dominios con resoluciones horizontales de 9, 3 y 1 km. Se evaluaron diferentes combinaciones de siete esquemas de microfísica, tres cumulus y tres capas límites planetarias en función de su capacidad para simular la precipitación horaria durante este evento de lluvia. Los índices estadísticos (MB = -0.69; RMSE = 4.11; MAGE = 1.74; r = 0.55; IOA = 0.66, y FAC2 = 0.58) y los gráficos de series temporales mostraron que las configuraciones más adecuadas para este evento meteorológico fueron las de Mellor-Yamada-Janjić, Grell-Freitas y Lin para los esquemas de capa límite planetaria, cumulus y microfísica, respectivamente. Los resultados se compararon con los datos medidos en las estaciones meteorológicas ubicadas en la ciudad de Salvador. El modelo WRF simuló bien la llegada y ocurrencia de este evento climático extremo en una región tropical y costera, considerando que la región ya tiene características convectivas intensas y está constantemente influenciada por brisas marinas, las cuales podrían interferir con los resultados del modelo y comprometer el desempeño de las simulaciones.
