Time lags variance of groundwater level response to precipitation of Jinan karst spring watershed in recent 50 years

Recent 50 years, both groundwater level data and precipitation data were devided into several time periods in this paper. The time lags of groundwater levels to precipitation were quantitatively analyzed by using the method of cross wavelet analysis; and the relationships between the time lags and groundwater abstraction etc. were also studied by correlation analysis. The results show that, (1)The main periodicities of both groundwater level and precipitation are 1 a. (2)The time lags of groundwater levels of discharge area are 83.44-161.24 d and 88.62-150.56 d by the two divisions, while the time lags of runoff area are 67.87-81.66 d and 76.58-82.21 d, respectively, which is significantly less than the time lags of discharge area. (3) According to precipitation, a trend that the less the precipitation and the larger the time lag can be concluded in both runoff and discharge areas. (4)Taking into account the groundwater levels, the time lag becomes larger while the groundwater level is lower in discharge area. This case does not occur in runoff area. (5)Correlation relationship is obvious between the time lag and groundwater exploitation and spring discharge. The larger the exploitation and the less the spring discharge, the larger the time lags. Analyzing time lag variances of groundwater levels to precipitation can provide knowledge on their nonlinear coupling processes, which will be benefit to the forecast of groundwater levels.