Variations in longest consecutive dry days in warm half year over Northern China

Daily precipitation data in northern China are selected to construct the time series of the longest consecutive dry days in warm half year (April-September) in northern China. The empirical mode decomposition (EMD) method is used to obtain intrinsic mode functions (IMFs), by which variations of the original series are analyzed on various time scales. By use of wavelet analysis and M-K method, sudden jump points of the series are detected. Results show that the drought variation was characterized by 3-4year and 8-10year oscillation patterns during the recent 50 years, and mainly composed of IMF1, IMF2 and IMF3. There was an increasing trend of the longest consecutive dry days in warm half year in the northern China. The longest consecutive dry days increased significantly in 1960 and 1994 in the northern China, which are close related with the occurrences of drought phenomena.