Diurnal cycles of one season with precipitation extremes in southeastern South America: comparison between models, resolution and observational datasets

Over the southeast of South America, the extended warm season from October 2009 to March 2010 registered a great number of extreme precipitation events. In this study, we evaluated the ability of the regional climate models and observational datasets to simulate observed features of the precipitation mean diurnal cycle observed during this period. WRF (two versions – 3.8.1 and 3.9.1) and RegCM4.7.1 simulations, with a horizontal grid spacing of 20 km (which uses both convective and large scale precipitation schemes) and 4 km (the precipitation is solved only by the microphysics scheme - convective permitting - CP), were analysed. We also considered six observational gridded precipitation datasets (MSWEP, CMORPH, PERSIAN, TRMM, ERA5 and GSMAP). These data and simulations are compared against 51 local observations of the precipitation every 3 hours. For the 51 stations, the observed diurnal cycle presents a great variety of patterns (time of maximum, minimum, amplitude, and double peaks during the day), but it is noted a slight predominance of more intense peaks at 06, 09 and 12 local time, characterizing the morning precipitation in the region. Comparisons of the six observational gridded datasets with the in situ data indicate a small outperformance of CMORPH and ERA5 to reproduce the main features of the observed diurnal cycle. At 20 km resolution, the simulations are not able to capture the diversity of diurnal cycles shown by in situ data. CP simulations capture better the great variety of the precipitation diurnal cycles shown by in situ observations. Specifically, for WRF-CP there is a shift in the afternoon peak at 15 LT to the morning-early afternoon (from 6 to 12 LT), while in RegCM4-CP there is a decrease in the number of simulated diurnal cycles peaking at dawn and a displacement of some peaks from dawn (03 LT) to morning (09 LT). The increase in the diversity and shift to morning-early afternoon peaks (6 to 12 LT) are the features showing the greatest agreement between CP simulations and in situ observations of the diurnal cycle of precipitation.