Numerical Evaluation of the Influence of Urbanization in the Convection and Precipitation Patterns in the Metropolitan Region of São Paulo

Abstract Studies indicate that urban areas can become Urban Heat Islands (UHI) mainly due to the lack of green areas, high emissions of air pollutants and presence of civil materials, which absorb and retain more heat for a longer time than natural, which makes the temperatures of these sites higher than the surrounding areas. The influence of convective processes in rain formation in order to modify the rainfall region are discussed in the scientific world, since that processes also depend on the local temperature. In this context, the influence of urbanization on rainfall in the metropolitan region of São Paulo (MRSP) was assessed by means of statistical methods and numerical simulations. The WRF model was used with different soil type and usage settings, namely: 1 - current urban sprawl; 2 - expanded urban area; 3 - urban sprawl replaced by native forest. The numerical simulations were performed for events in which convection played a key role in setting rainfall. The analysis of time series of precipitation has shown indications of change of pattern behavior in the MRSP mainly in the 1980s and 1990s and 2000 to the present, although it has not shown tendency to increase or decrease the average rainfall in the MRSP. The simulation results highlighted the strong influence of urbanization on atmospheric dynamics and consequently the UHI of the MRSP, culminating in severe and concentrated convective precipitation event around and inside the urban area. Simulations in which urbanization was changed to native forest, precipitation occurred, in most cases, in a more spatially distributed way and with less intensity cores.