Intra-Annual Non-Uniform Characteristics of Extreme Precipitation Process Events in China

Extreme precipitation process events (EPPEs) with long durations exhibit greater hazard potential and serve as a crucial trigger for basin-wide floods. Studying the intra-annual inhomogeneous characteristics of such EPPEs is of great significance for flood disaster early warning and risk management. Based on daily precipitation data from 610 stations in China during 1960 to 2009, this study introduces two new parameters, namely the concentration degree and the concentration period of EPPEs, to characterize their temporal distribution. Using trend analysis and Morlet wavelet analysis, the study investigates the intra-annual non-uniformity of annual extreme precipitation process events in China. Results indicate that both the concentration degree and concentration period of EPPEs exhibit a spatial pattern of “low-high-low” from southeast to northwest, whereas the spatial distribution of their standard deviations shows an opposite pattern. The area-averaged series of concentration degree and concentration period in the four major regions of China (western, northern, southern, and southwestern regions) demonstrate distinct interannual variations and oscillations. The EPPEs in Northern, Southern, and Southwest China have shown a tendency toward concentration, leading to an increased risk of multiple flood disasters occurring intensively within a certain period of the year. In contrast, those in Western China have exhibited a tendency toward dispersion, with the occurrence time of annual flood disasters tending to be discretized. Except for Southern china, EPPEs in other sub-regions have shown an advancing trend—indicating an elevated flood risk during the post-flood season in Southern China and a heightened flood risk during the pre-flood season in the other regions. A significant negative correlation coefficient is found between the concentration degree of EPPEs and extreme precipitation amount, indicating that a higher concentration of EPPEs corresponds to a smaller extreme precipitation amount, particularly along the coastal areas of south China.