Urban climate characteristics simulated by convection-permitting models over the main metropolitan regions of southeastern Brazil

The urbanization process transforms the natural environment into built structures, and the presence of cities can modify the local climate, creating a coupled urban soil-surface-atmosphere system that can be termed urban climate. Convection-permitting models (CPMs) can represent organized vertical transport of heat and moisture on the model grid and explicitly  solve  moist  convection as well as incorporate the land-use specifications related to the urban areas. Both features can improve simulations of the local climate. In this context, our objective is to investigate the ability of CPM simulations, carried out with RegCM5 and WRF, to reproduce observed characteristics associated with the urban climate in main metropolitan regions (MRs) of southeastern Brazil. For the  2018-2021 period, we compare two CPM simulations (4-km grid spacing) against local observation and  urban climate analysis from the literature. Across southeastern Brazil, the CPM simulations are able to capture: a) the spatial patterns of rainfall and temperature, with smaller biases than those in previous coarser resolution simulations, and b) the phase and amplitude of the diurnal cycles in the MRs, improving the representation of local climate features. More specifically, for the São Paulo MR, the afternoon warming in urban areas is well simulated by both models, whereas the nocturnal-dawn heating is better represented by RegCM5 than by WRF; for the Rio de Janeiro MR, the observed combination of daytime cooling driven by sea-breeze circulation and nighttime-dawn urban heating is realistically simulated by both models. Our comparisons of CPMs with local observations highlight the potential of CPM simulations for investigating future changes in urban climate under climate-change.