Polarimetric Radar Signatures and Rainfall Performance during an Extreme Precipitation Event in Southern China

From 2200 UTC, 29 August 2018 to 2200 UTC, 30 August 2018, the 24-hr precipitation accumulation of 1089.6 mm measured by rain gauge in Gaotan Town set a record in China. The flash flood caused by heavy precipitation of monsoon depression during this extreme precipitation event brought high socioeconomic losses and casualties to Guangdong Province. Dual-polarization radar has proven to be an efficient tool for monitoring large-scale extreme precipitation systems as such. The dual-polarization radar also has better performance for quantitative precipitation estimation (QPE) than conventional single-polarization radar. Therefore, China Meteorological Administration has initiated the effort to upgrade all the operational weather radar systems with dual-polarization capability. The eight S-band radars in Guangdong Province were the first batch of the dual-polarization upgrade; in particular two of them (Guangzhou and Meizhou radars) have captured the entire process of this extreme event. This paper investigates the synoptic environment that led to this extreme precipitation. In addition, this study extends a polarimetric radar rainfall system for local applications in southern China. Polarimetric observations from these two radars during this extreme event are used to quantify and analyze the QPE performance of various radar rainfall algorithms. The results show that the blended radar rainfall algorithm performs the best: the normalized mean bias is -26.36%, the normalized standard error is 39.73%, and the Pearson correlation coefficient is 0.92.