Some aspects of severe weather in the Metropolitan Area of São Paulo

The Metropolitan Area of São Paulo (MASP) is one of the largest urban environments of the world. Flash floods in the summer and heavy pollution in the winter are a common place. There are more than 500 inundation areas within the MASP. Recent studies of convective events under the 1997/1998 El Niño conditions have shown higher rainfall accumulations and higher probabilities of heavy precipitation over the MASP. These events were related to the local circulation generated by the heat island and the sea breeze. Heavier rainfall events also tend to produce higher density lighting flashes that damage the electrical power supply very often. Additionally, strong gust winds also affect two major airports within the MASP. This paper presents a hydrometeorologic analysis of some significant convective events. Since the MASP is growing continuously without any effective public policy, extreme weather conditions tend to get worse. Therefore, good nowcasting procedures can effectively mitigate human and material losses in the MASP. Surface data indicate that the dew point temperature can be used as an indicator of the timing and severity of the convective systems. Also, lighting and weather radar measurements show a strong correlation between the vertically integrated water content (VIL) and the lighting flash density.