Eventos extremos de chuva em Salvador, Bahia: condições atmosféricas e impactos ambientais

Abstract

Extreme rainfall events and their environmental impacts upon the city of Salvador, Bahia, on 21 April and 12 June 2006 are analyzed in this study. Interaction between the mesoscale and the synoptic scale was investigated. Surface and upper air observational data, NCEP/NCAR grid point data, meteorological satellite images and data on environmental impacts provided by the Civil Defense of Salvador (CODESAL) were used in the analysis. During the heavy rainfall event of 21 April, 55 mm of rain fell between 5 and 7 LT in the morning, causing landslides and inundations. Very weak winds throughout the troposphere in Salvador and strong winds in the upper troposphere in Caravelas were observed in the day before the event, in conjunction with high moisture content and maximum convective available potential energy of 1,680 J/kg in Salvador. This event is caused by a trough formed in the eastern coastal area of Northeast Brazil in association with the northeastward advance of an austral frontal system. Ascending motion throughout the troposphere and moisture convergence in the lower troposphere favored convection development. During the extreme event of 12 June, 51 mm of rain fell between midnight and 3 LT. A high number of occurrences were registered by the CODESAL. Weak winds throughout the troposphere in Salvador and Caravelas and maximum convective available potential energy of 3,233 J/kg in Salvador were diagnosed in the day before the event. Deep convection organized on the mesoscale characterizes this event caused by the penetration of an easterly disturbance whose westward propagation was evident on the wind field at 500 hPa level and on meteorological satellite images.