中国大陆地区小时极端降水阈值的计算与分析

利用广义极值分布和百分位两种阈值确定方法，对我国465个气象站点不同极端程度的小时降水强度阈值进行了分析。广义极值分布结果表明，重现期为2、5、10、50a的降水强度阈值具有一致的空间分布特征：华南沿海阈值最高，长江中下游地区北部、四川盆地西部、华北地区东部次之，云南中西部、华北西部和东北西部阈值相对更低，最小值出现在我国西部地区。百分位法得到的阈值空间分布呈现出与广义极值分布结果较为一致的东南大、西北小的整体特征。考察465站中位数发现，第99．9百分位的强度阈值与二年一遇降水的阈值接近。具体分析各站第99．9百分位降水阈值对应的重现期发现，长江流域及其以南地区重现期大多低于2a；35°N一带重现期长于4a；我国北方和西北部分地区重现期长于8a。

Calculation and analysis of the thresholds of hourly extreme precipitation in mainland China

Using two methods in thresholds definition, Generalized Extreme Value （GEV） distribution and percentile measurement, the thresholds of hourly rainfall intensity at 465 stations in mainland China are analyzed on different extreme scales. GEV distribution shows that the thresholds for 2, 5, 10, and 50-year return period share an identical spatial distribution, which exhibits highest values in coastal region of southern China; higher values in the north of the middle and lower reaches of the Yangtze River valley, west of Sichuan basin, and east of northern China; lower values in the midwest of Yunnan, west of northern China, and west of northeast China; lowest values in the western Chi- na. Meanwhile, the percentile results have the same distribution pattern as GEV outcomes on a whole, which present higher thresholds in southeast and lower thresholds in northwest. The medians at 465 stations are analyzed. The results indicate that intensity thresholds of the 99.9th percentile are close to intensity thresholds of 2-year return period. Having converted the thresholds of the 99.9th percentile to return period level, it is shown that the return periods are under 2-year in Yangtze River valley and its southern area; longer than 4-year along 35°N; longer than 8-year in parts of northern China and northwest China.