Response of shallow groundwater depth to climate change and human activity in Weihai, China

According to shallow groundwater depth data in 1 January from 1982 to 2006 of 44 monitoring wells, annual precipitation data of 21 rain gauges, and meteorological data of 4 stations, the response of shallow groundwater depth to climate change and human activity was evaluated in Weihai, China. The variations of shallow groundwater depth in Weihai were analyzed using non-parametric Mann-Kendall test. Decreasing trends in shallow groundwater depth were found in 25 monitoring wells (15 monitoring wells significant at 95% confidence level) from 1982 to 2006, while increasing trends were found in 15 monitoring wells (3 monitoring wells significant at 95% confidence level). The average trend in shallow groundwater depth is decreasing with 72.7 mm/10a. Increasing trends in annual precipitation were found in all the 21 rain gauges except one gauge, and the trends slopes are between 7.7mm/10a and 120.2mm/10a. Decreasing trends in groundwater exploitation volume (using data from 1991 to 2005) was also found. The influences of changes in precipitation and groundwater exploitation on groundwater depth were analyzed. The correlation coefficient between shallow groundwater depth and annual precipitation from 1982 to 2006 is -0.66, and the correlation coefficient between shallow groundwater depth and groundwater exploitation from 1992 to 2006 is 0.57. The increasing in annual precipitation was the main reason, while the decreasing in groundwater exploitation (using data from 1991 to 2005) was the other reason. A binary regression model between shallow groundwater depth, precipitation, and groundwater exploitation was developed: H=-0.001P+0.06W+2.31 where H is average shallow groundwater depth (m), P is average annual precipitation (mm), W is shallow groundwater exploitation volume (100,000,000 cubic meters). The model performs well to predict shallow groundwater depth from 1992 to 2006 using precipitation and groundwater exploitation data (with deterministic coefficient 0.78). Under different scenarios conditions of groundwater exploitation, the shallow groundwater table deepens with decrease in precipitation, and the average shallow groundwater depth approximates 2 m if the precipitation is the minimal value in history. This study could be used to analyze the influences of climate change on shallow groundwater, and is the bases for water resources management.