Study on SpatioTemporal Distribution Characteristics of Hourly Heavy Rainfall in Sichuan and Chongqing from May to September During 1980-2012
Based on the qualified hourly precipitation data of 123 stations in Sichuan Province and Chongqing City from 1980 to 2012, the multiple spatiotemporal distribution characteristics of the frequency, the intensity and the duration of hourly heavy rainfall (HHR) during main flood season from May to September are investigated. The main conclusions are as follows. The annual variation and diurnal variation of frequency during 1980-2012 are nearly identical at the thresholds above 20 mm, 30 mm and 50 mm per hour. The average annual frequency of HHR is 504, 184 and 28 respectively. According to the dynamic convergence lifting over mountain terrain and the forcing of large mountain gradient in the west of Sichuan and Chongqing Basin, the high frequency areas of HHR at the thresholds above 20 mm per hour distribute in Longshan Mountains in the northwest of the basin and the transition zone between the surrounding area of Ya’an and Leshan and the southwest of basin. The diurnal peak of frequency mainly happens between 20:00 BT and 01:00 BT in the south of basin and between 02:00 BT and 07:00 BT in the central, north and east of the basin. The diurnal variation of different hours shows double active peaks with the first peak after the noon and the second peak between 20:00 BT and the next 07:00 BT. The events of short duration (2-6 h) mostly occur in the day time, yet the events of lasting 2 to 18 hours all happen between the nightfall and the next morning. The intensity, frequency and precipitation amount of the events of HHR at distinct beginning time are characterized by similar daily variation with the single active peak happening between 18:00 BT and 06:00 BT. The accumulating rainfall and the frequency of the HHR events are less during the day time (09:00-20:00 BT) than over night (21:00-08:00 BT), which means the HHR events are remarkable at night time.