Study on Regional Extreme Precipitation Events over South China during 1981–2020

Using 176 meteorological hourly precipitation data over the mainland of South China (Guangdong and Guangxi) and monthly reanalysis data from ERA5 (European Centre for Medium-Range Weather Forecasts, fifth reanalysis) during 1981–2020 and applying OITREE (objective identification technique for regional extreme events) and synthetic analysis, this study investigated the temporal and spatial characteristics of regional extreme precipitation event (REPE) over the mainland of South China. In addition, this study analyzed circulations in years with high and low REPE frequencies. The following conclusions are drawn from these investigations. In terms of frequency, periodic variations in the REPE frequency on the interannual scale are obvious and have clear monthly distribution characteristics that peak in May–June. For extreme intensity and impacted area, the intensity of most REPEs in Guangdong and Guangxi is approximately 130 mm d⁻¹, while that of few events is greater than 320 mm d⁻¹, and the impacted area of REPEs shows a considerable upward trend (about 310 km² a⁻¹). In terms of comprehensive intensity, the comprehensive index Z demonstrates a remarkable upward trend 0.05 (10 a)⁻¹, indicating that the intensity of REPE has a notable increasing trend. The annual accumulated precipitation of REPEs in the Greater Bay Area and northern Guangdong and their contribution to annual total precipitation exhibit a considerable upward trend, while in southern Guangxi, both parameters show a downward trend. In years with high REPE frequency, substantial water vapor transportation and intensive convergence of whole-layer moisture flux are noted over South China, while in years with low REPE frequency, relatively weak convergence of the whole-layer moisture flux divergence is observed. On days of normal precipitation events, South China is primarily dominated by weak southeasterlies at 850 hPa, while on days of REPEs, South China is located in the southeast of the cyclonic circulation and is affected by strong southwesterlies.