Abstract: Under the natural conditions, there is the dynamic balance between the groundwater and sea in the coastal region. However, the overexploitation of groundwater causes the imbalance between them, which also induces the various of environmental problems. The analysis methods of traditional time series cannot accurately reveal the dynamic variation characteristic in both time and frequency domains, while wavelet analysis methods provide convenient way to explore the dynamic variation characteristics and external influence factors of groundwater. The continuous wavelet transform and wavelet coherence analysis are used to analyze the time series data of groundwater level in three monitoring wells and precipitation in Rizhao area during the interval of 19962015. The results show that: The periodic characteristics of groundwater level variation in different aquifer categories are different. The groundwater level in Dishui monitoring well (pore water of shallow loose rocks) shows periodic variation characteristics which are one year, 45 a and 11 a. The groundwater level in Earthquake Bureau of Juxian well (bedrock fissure water) and Dongguan High School well (carbonate fissure karst water) show the periodic variation of 11 a  and the strong tendency of 14 a. The precipitation in Rizhao area shows several different periodic variations, including one year, 45 a, 11 a and the strong tendency of 14 a.  The periodic variation of precipitation in Rizhao area is the important influence factor on the variation of groundwater level which show the periodic variation of one year and several years.  The lag time between the groundwater change and the variation of precipitation in different aquifer type is different, which is the main reason for the diversity characteristic of groundwater level periodic variation in different aquifer type. 

Key words: groundwater regime, continuous wavelet transform, wavelet coherence, lag time, Rizhao area