Spatiotemporal characteristics of precipitation diurnal variations in Chongqing with complex terrain

Using the hourly precipitation data observed at 34 gauge stations in Chongqing during 1991–2012, the spatial and temporal characteristics of the precipitation amount (PA), precipitation intensity (PI), precipitation frequency (PF), and their diurnal cycles are analyzed. Results show that the PA increased from the western to eastern Chongqing in spring and autumn. The summer precipitation was dominant throughout the year, and the PA in the basin was larger than in the eastern and middle mountainous area, which was different from in spring and autumn. The nocturnal precipitation had a quasi-stationary feature. The diurnal peaks of the PA/PI/PF mainly appeared from midnight to early morning. The amplitude of the PF was significantly greater than that of the PI and thus determined the characteristics of diurnal variation of the PA. In terms of the distribution of peak time of precipitation, this study reveals a time lag indicating the peak time was later in the northeast than in the southwest Chongqing. The complex terrain played an important role in the difference of diurnal cycle of precipitation in different areas. The stations in the southwest Chongqing are largely located in the Sichuan Basin, while the stations in the eastern and middle Chongqing are located in the mountainous area surrounding the basin. By selecting 16 representative stations in two types of terrain for analysis, it is shown in the study that the amplitude of diurnal precipitation at the stations in higher terrain was weaker. Moreover, investigating the interval of precipitation associated with the diurnal distribution of lightning reveals that the enhancement of precipitation in the mountainous area in the afternoon was mainly caused by the short-time strong rainfall resulting from the convection.