Spatial and Temporal Characteristics of Extreme Hourly Precipitation in Sichuan Province Based on Spatially Dense Rainfall Observation

Based on the hourly precipitation data of 3454 stations with dense space in Sichuan Province and DEM （Digital Elevation Model） data with horizontal accuracy of 30 m， the temporal and spatial distribution characteristics of extreme hourly precipitation in 7 regions of Sichuan Province in recent 10 years were analyzed， and the relationship between high frequency extreme precipitation and complex terrain was discussed.The results showed that： （1） In recent 10 years， the frequency of extreme hourly precipitation with hourly rainfall ≥100 mm in Sichuan Province has increased significantly with the growth rate of 6.4 times·（10a）-1.（2） The sub-seasonal variation of extreme hourly precipitation frequency was more significant than that of extreme rainfall intensity， with the maximum monthly increase of 3.7 times and 0.2 times， respectively.In addition， the occurrence time of peak frequency was delayed with the increase of extreme hourly precipitation threshold.（3） The frequency of extreme hourly precipitation was significantly higher at night than during the day， and the occurrence time of peak-valley value and high-frequency concentration period were different in different regions， and the frequency peak appears gradually from south to north and from west to east.（4） The diurnal variation of extreme rainfall intensity was much weaker than that of extreme hourly precipitation frequency， and the extreme rainfall intensity of most stations in the basin was higher than the regional average， but the opposite was true in western Sichuan Plateau and Panxi area.（5） The distribution characteristics of extreme hourly precipitation frequency and cumulative rainfall in different regions were closely related to topographic uplift and topographic convergence in this region， and the increase of extreme hourly precipitation caused by topographic forced uplift in the western part of the basin was roughly below 1400 m.（6） The slope of high frequency extreme hourly precipitation sites in the basin was mainly eastward， and the slope of high frequency sites in the southwest of the basin was larger than that in the northwest of the basin.The number of maximum extreme hourly cumulative rainfall sites in the Western Sichuan Plateau and Panxi area increased first and then decreased with the slope， and the peak value was located in the slope， but the decrease was more rapid in Panxi area than in the Western Sichuan Plateau.