Radar QPE for Extreme Precipitation Using the Lontras S-Band Dual-Pol Radar in Santa Catarina, Brazil

An extreme rainfall event over eastern Santa Catarina State, Brazil, during 10-12 January 2018 caused a record flooding during summer season. A 409 mm was recorded in three days in rain gauge network, but it was not produced by deep convection as expected in summer. During all three days, a continuous stratiform rain ranging from 1 to 8 mmh-1 was predominant. At the end of 10th January and early 11th January a development of severe convective storms over Florianopolis City, Capital of the Santa Catarina State was observed. At the rain gauge network were recorded values of 31.4 mm/h, 25.8 mm/h and a historical record of 31.2 mm in 10 minutes, what generate severe damages due to flash flooding. For the analysis of rainfall spatial distribution we used Quantitative Precipitation Estimate (QPE) fields obtained by Z-R relationships from a new Dual Polarization S-Band Weather Radar located at Lontras City, about 70 km distance from Florianopolis. It was compared six Z-R relationships: traditional Marshall-Palmer (a=200, b=1.6), Joss (a=500;b=1.5), two other Z-R relationships based in studies developed in Brazil, Calheiros (a=236;b=1.5) and Santos (a=52;b=2.7), and two polarimetric Z-R relationships including reflectivity (Z), differential reflectivity (ZDR) and specific differential phase (KDP). A discussion about the efficiency of the QPE for the historically observed rainfall events was lead in a sense of predicted flash foods in urban areas. The tradicional Marshall-Palmer Z-R relationship show good results for the stratiform pattern of all events, but overestimated all convective cells. Using KDP and ZDR variables, it was possible to detect the rainfall peaks, but not exactly as observed in rain gauges. However, these polarimetric relationships could be useful for hydrometeorological purposes with a good skill. The persistent northeastern maritime influx of moisture in the area lead to a stratiform pattern during the three days. A mesoscale analysis was conducted to understand the precipitation pattern during this special event to clarify how the nowcasting could be made for hydrological purposes.The precipitation peaks were generated by strong convection triggered during a zonal propagation of a mid-level shortwave trough over the continental. Although the low reflectivity observed in S-Band Weather Radar the flood was caused by a persistent rainfall coupled with strong and fast convection episodes.