Thesis Defense: Impacts of urban growth on severe weather events in the Metropolitan Area of São Paulo (MASP)

1. Prof. Dr. Edmilson Dias de Freitas - IAG/USP
2. Prof. Dr. Rachel Ifanger Albrecht - IAG/USP – on videoconference
3. Prof. Dr. Ernani de Lima Nascimento – UFSM – on videoconference
4. Prof. Dr. Wallace Figueiredo Menezes - UFRJ– on videoconference
5. Dr. Andréia Bender – CEMADEN – on videoconference

inglês: Over the past decades, several studies have shown that urbanized regions impact storms, primarily by increasing precipitation. In the MASP, especially during the summer, heavy rains are responsible for social and economic damages. Considering the existing vulnerability of the urban population to storm events and the expected population growth, it becomes evident the need to understand these impacts in future urban scenarios. Thus, in this study, three modifications were proposed: land cover and land use change for the year 2050, including urban growth and other anthropogenic modifications in the region, increased anthropogenic heat flux for 2050, and expansion of the area occupied by tall buildings. The impact of each parameter and their interaction on convection and precipitation were evaluated for two storm events in the MASP. Urban area expansion and increased anthropogenic heat flux produced more intense updrafts and precipitation rates throughout the two events. Stronger updrafts increased the formation of rain and hail in convective cells, resulting in more intense precipitation rates and greater accumulated precipitation. In both events, urban growth contributed to the expansion of the rain coverage area. Additionally, the results indicated that the increase in heat flux from anthropogenic sources had a greater contribution to the intensification of rain than urban expansion. Furthermore, the expansion of the verticalized area decreased the accumulated precipitation in the urban area. In this case, except for the scenario with all three parameters combined in the second event, the area affected by rain in the MASP was smaller than in the control simulation in all these scenarios, although the precipitation rates were more intense. Some factors were considered responsible for these effects: more intense updrafts due to intensified convergence at the external boundaries of the urban area, decreased LCL height, increasing rain formation in the warm part of the cloud, and increased low-level humidity in scenarios with increased anthropogenic heat flux. Considering all the results, the scenario with land use change combined with increased anthropogenic heat flux resulted in the highest average accumulation in the MASP in both events, configuring the most problematic future scenario for the region's population. However, all future scenarios analyzed here impacted the rain pattern in storm events, and thus, urban expansion plans and modifications should be evaluated with caution to mitigate possible related damages.

Palavras-chave: BRAMS, urbanization, precipitation, urban heat island, factor separation analysis.