近40 a西藏怒江流域极端降水事件的时空变化

利用西藏怒江流域1971-2010年9个台站逐日降水量资料，采用第99个百分位值确定了不同台站的极端降水阈值，对流域极端降水事件的时空特征进行分析。结果表明：西藏怒江流域极端降水阈值为20.6～33.8 mm，分布与年降水量的走向基本一致。近30 a那曲地区大部、八宿和察隅最大日降水量为增加趋势，尤其是察隅，增加了5.2 mm•(10a)^-1；极端降水频数丁青、八宿和察隅趋于增多，其他各站倾向于减少(-0.06～-0.41 d•(10a)^-1；年极端降水量察隅以29.4 mm•(10a)^-1的速度明显增加，左贡变化不大，其他站点呈减少趋势，为-1.0～-27.2 mm•(10a)^-1；年极端降水强度那曲、索县、左贡和察隅为增强趋势，为0.6～6.2 mm•d^-1•(10a)^-1，比如、洛隆和八宿无变化，安多和丁青呈减小趋势。极端降水频数、极端降水量、日最大降水量、极端降水强度在20世纪90年代前均存在4～5 a的显著周期，在2000年以后均存在2～4 a的显著周期。

On Extreme Precipitation Events in the Nujiang River Basin in Tibet in Recent 40 Years

Based on the daily precipitation datasets recorded by 9 meteorological stations in the Nujiang River Basin in Tibet during the period from 1971 to 2010, the thresholds of extreme precipitation at these stations were defined using 99 percentile values, and the spatiotemporal change of extreme precipitation events in the basin was analyzed. The results show that the thresholds of extreme precipitation varied in a range of 20.6-33.8 mm in the Nujiang River Basin, and the spatial distribution of extreme precipitation thresholds was consistent with annual precipitation. In recent 30 years (1981-2010), the maximum daily precipitation was in an increase trend in most areas including Nagqu, Baxoi and Zayu, especially in Zayu where the increase rate was 5.2 mm•(10a)^-1. The frequency of extreme precipitation tended to an increase in Dengqen, Baxoi and Zayu, but it decreased at other stations with rates of -0.06--0.41 d•(10a)^-1. The annual extreme precipitation increased significantly with a rate of 29.4 mm•(10a)^-1 at Zayua, changed slightly at Zogang, and was in a decrease trend with rates of -1.0--27.2 mm•(10a)^-1 at other stations. In addition, the extreme precipitation intensity increased with rates of 0.6-6.2 mm•d^-1•(10a)^-1 at Nagqu, Sog, Zogang and Zayu, it was in a decrease trend at Amdo and Dengqen, but there was no change at Biru, Lhorong and Baxoi. It was also found that there was a significant 4-5 year period of frequency of extreme precipitation, maximum daily precipitation, extreme precipitation and extreme precipitation intensity before the 1990s, and a significant 2-4 year period after 2000.