Characteristics of precipitation diurnal variation in the rainy season of Beijing in 2009–2020

This study researched the characteristics of hourly precipitation, including precipitation amount (PA), precipitation intensity (PI), and precipitation frequency (PF). We used hourly precipitation data from 20 national meteorological stations and 445 automatic meteorological stations in Beijing from May to October 2009–2020. The daily mean precipitation amount ranges from 2.0 to 3.2 mm, with some high values stretching from the northeast to the southwest. In general, diurnal variation of mean PA and PI in Beijing are synchronous with the peak phases at about 22 Local Standard Time (LST) and the valley phases at 12 LST; PF keeps low between 12 and 15 LST but high from 22 to 7 LST the next day. Hourly precipitation over 4.6 mm (the 90th percentile of all valid hourly precipitation records) accounts for over 50% of total PA and about 10% of PF. We also performed the empirical orthogonal functions (EOF) analysis on hourly mean PA. EOF1 (39%) explains widespread and continuous precipitation processes, and EOF2 (8%) explains regional differences influenced by topography and the underlying surface. Beijing is divided into three regions by EOF2 loadings: mountain, urban and suburban. The diurnal variations of PA are opposite in the mountain and plain (urban and suburban) areas. Specifically, the daytime rainfall is more in the plain areas but less in the mountain areas, whereas the reverse is true for the nighttime rainfall. Despite the consistent diurnal variation over the urban and suburban areas, the fluctuation of stations is more intensive in urban areas.