近50年东江流域极端降水事件变化特征

基于东江流域1960年-2009年逐日降水数据资料,运用Mann-Kendall非参数检验、滑动T检验和Morlet小波分析法,分析了近50年来东江流域极端降水事件的时空变化特征.结果表明,东江流域极端降水指数的多年平均值及变化趋势的空间分布存在明显区域差异.极端降水指数增幅较大的区域位于流域下游,以增城为中心的地区升幅尤为明显,流域上、中游地区变化幅度相对较小.近50年来,整个东江流域极端降水指数未表现出明显的变化趋势,除连续湿日数外,其他极端降水指数仅呈现出弱的上升趋势.东江流域的极端降水与年降水量密切相关.流域极端降水指数的突变特征并不一致,5日最大降水量、强降水日数、连续干日数及连续湿日数分别在1984年-1985年、1973年、2005年和1978年前后发生突变.近50年东江流域极端降水事件变化,普遍存在着22～23年左右的主周期和7～8年左右的次周期.

Climatic Characteristics of Extreme Precipitation Events in the Dongjiang River Basin in the Last 50 Years

Variation in precipitation extremes in the Dongjiang River basin from 1960-2009 were analyzed based on daily precipitation data from 12 meteorological stations within and adjacent to the Basin. The methods of linear regression, moving t-test, Mann-Kendall test and continuous wavelet transform were employed to delineate the rate of change, abrupt change points, statistical significance of the trends, and periodicity of extreme precipitation indices. The results showed that in most stations from the Dongjiang River basin no significant monotonic trend was found for six selected extreme precipitation indices, including the maximum 1-day precipitation (RX1day), the maximum 5-day precipitation (RX5day), the heavy precipitation days (R25mm), the total extreme daily precipitation amount (R95), the maximum consecutive dry days (CDD), and the maximum consecutive wet days (CWD). In the last 50 years, the regional average RX1day, RX5day, R25mm, R95 and CDD presented a non-significant positive trend at the rate of 0.42 mm/10a, 0.57mm/10a, 0.37day/10a, 9.98mm/10a, and 1.83 day/10a, respectively, whereas only CWD presented a non-significant negative trend with the change rate at -0.17 day/10a. Except for CDD, the extreme precipitation indices were closely associated with annual total precipitation in the basin. The extreme precipitation indices exhibited some spatial variation. Larger change magnitude in extreme precipitation indices with positive trends occurred at the lower reaches of the Dongjiang River, with the largest observed at Zengcheng. The abrupt change point of each extreme precipitation index in the Dongjiang River basin was inconsistent. Abrupt change points of RX5day, R25mm, CDD and CWD were at 1984-1985, 1973, 2005, and 1978, respectively, and no abrupt change occurred for RX1day and R95. The major oscillating periods of RX1day, RX5day, R95, CDD, and CWD were found to 23a, while R25mm was 22a. The minor oscillating periods of RX1day, RX5day, and R95 were 7a, R25mm and CWD were 8a, and the CDD was 4a. Based on our finding we conclude that most extreme precipitation indices in the Dongjiang River basin from 1960-2009 existed two common oscillation cycles, namely, 7~8 years (minor cycle) and 22~23 years (major cycle).