从小时尺度考察中国中东部极端降水的持续性和季节特征

相对于日降水量,小时尺度降水资料可以更准确地反映降水强度并描述降水过程,因而更适用于极端降水阈值确定及其特性研究.利用广义极值分布估计中国321个站最大小时降水量的分布函数,确定了5a重现期的小时降水强度阈值.阈值的空间分布呈现出明显的地域差异,西北地区阈值偏低,华北地区、长江中下游地区、华南沿海地区和四川盆地西部地区为高阈值中心.取各站5a一遇极端降水事件对其持续性特征和季节特征进行分析,发现在沿海地区、长江流域和青藏高原东坡极端降水事件的平均持续时间较长(超过12h);中国北部地区持续时间较短.在具有较大海拔落差的复杂地形区,极端降水事件较平原地区更快地发展到峰值.华南地区4月就可有极端降水事件出现,而中国北方地区要到6月底才出现极端降水;全中国大部分地区的年最晚极端降水在8-9月,但沿海地区、大陆南端和西南地区南部的少数站点在10月以后仍有极端降水发生.

Duration and seasonality of the hourly extreme rainfall in the central-eastern part of China

Compared with daily rainfall amount, hourly rainfall data arc able to represent the rainfall intensity and rainfall process more accurately, and thus more suitable for the studies of extreme rainfall events.The distribution functions of annual maximum hourly rain-fall amount for the 321 stations in China arc quantified by the Ucneralized Extreme Value (UEV) distribution, and the threshold values of hourly intensity for 5-year return period arc estimated.The spatial distributions of the threshold exhibit significant regional differenecs, with low values in northwestern China and high values in northern China, the middle and lower reaches of the Yangtze River, the coastal region in southern China, and the Sichuan basin.The duration and scasonality of the extreme precipitation with 5-year return periods arc analyzed.The average duration of extreme precipitation events exceeds 12 h in the coastal region, the Yangtze River valley, and the eastern slope of the Tibetan Plateau.The duration in northern China is relatively short.The extreme precipitation events reach the maximum intensity more quickly in the mountain regions with larger elevation differences than those in the plain areas.hhere arc records of extreme precipitation as early as April in southern China, while the extreme rainfall in northern China will not occur until late June.At most of the stations in China the latest extreme precipitation happens in August or September.The extreme rainfall later than Oetober can be found only at a small portion of stations in the coastal regions, the southern end of the continent, and the southern part of southwestern China.