Climatic Characteristics of Extreme Precipitation Events in the Dongjiang River Basin in the Last 50 Years
近50 年东江流域极端降水事件变化特征

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).