| The northwest of Beijing,Tianjin and Hebei is an important water conservation area and ecological barrier for Beijing and Tianjin,and also an important supporting area for the implementation of the strategy of"coordinated development of Beijing,Tianjin and Hebei".In order to reveal the temporal and spatial evolution law of groundwater level,the driving factors of groundwater level change and the way of sustainable utilization of groundwater resources in the northwest of Beijing,Tianjin and Hebei,the temporal and spatial evolution of groundwater level in four geomorphic units of Bashang Plateau,Chaixuan Basin,Zhuowai Basin and Yuyang Basin in Zhangjiakou area was analyzed by using 56 continuous observation data of groundwater level from 1981 to 2015?At the same time,using spss22.0software to build a stepwise multiple regression model to predict the temporal and spatial evolution of groundwater level in four geomorphic units in the future,in order to provide theoretical guidance for the rational utilization and allocation of water resources in Zhangjiakou area,as well as the conservation of water resources and ecological functions on the northwest of Beijing,Tianjin and Hebei,and also for the region scientific basis is provided for evaluation,management and decision-making of groundwater resources.The main conclusions are as follows:(1)According to the time variation of groundwater level,from 1981 to 2015,the groundwater level of four geomorphic units in Zhangjiakou,i.e.Bashang Plateau,Chaixuan Basin,Zhuohuai Basin and Yuyang Basin,as well as the counties under their jurisdiction,showed a general downward trend,and the downward rate has gradually increased since the mid-1990s.From 1981 to 1996,the groundwater level of Bashang Plateau and the counties under its jurisdiction fluctuated slightly,with a variation of?±0.46m;from 1996 to 2008,the groundwater level fluctuated and decreased gradually,with a decrease of 1.83m?4.35m;from2008 to 2015,the groundwater level slowed down,with a variation of?±2.86m.From 1981 to1998,the groundwater level in Chaixuan Basin,Zhuohuai Basin and the counties under their jurisdiction showed a fluctuating downward trend,with a drop of?3.18m and?0.86m respectively;from 1998 to 2015,the water level in Chaixuan Basin and Zhuohuai Basin decreased rapidly in a near linear trend,with a drop of 13.94-20.83m and 4.43-9.24m respectively.From 1981 to 1988,the water level in the Yuyang Basin showed a small fluctuation upward trend with a variation of?±0.4m;from 1988 to 2003,it showed a rapid fluctuation downward trend with a decrease of 1.99?3.9m;from 2003 to 2015,it showed a slow fluctuation downward trend with a variation of?±3.06m.(2)From the perspective of the spatial change of groundwater level,the spatial change of groundwater level in four geomorphic units in Zhangjiakou area from 1981 to 2015is shown as follows:water level drop of Plateau on dam(3.59m)<water level drop of Yuyang Basin(3.6m)<water level drop of Zhuohuai Basin(7.17m)<water level drop of Chaixuan Basin(20.41m).Among the counties under the jurisdiction of Bashang Plateau,Kangbao County has the smallest water level drop of 1.06m,Zhangbei County has the largest water level drop of 6.84m,and Shangyi County in Guyuan County has a water level drop of2.53-2.97m.Among the counties under the jurisdiction of Yuyang Basin,the water level drop of Yuxian County and Yangyuan County is 1.22m and 7.14m respectively.Among the counties under Zhuolu Huailai Basin,Zhuolu county and Huailai County have water level drop of 9.66m and 5.3m respectively.Among the districts and counties under the jurisdiction of chaixuanbasin,the water level drop in Qiaoxi District and Wanquan District is the largest,23.57m and 21.49m respectively;the water level drop in Xiahuayuan District is the smallest,6m;the water level drop in Qiaodong District,Xuanhua District and Huai'an County is16.99-17.48m.(3)From the driving factors of groundwater level change,the correlation between groundwater level change and precipitation,evaporation,temperature and other natural factors of four geomorphic units in Zhangjiakou area is relatively low from 1981 to 2015,but with the output value of the first,second and third industries,the total population at the end of the year,the common cultivated land area,the effective irrigation area,the total grain output,the total vegetable output,the total pork,cattle and mutton output and other social factors The correlation of social and economic factors is very high,so social and economic factors are the leading factors driving the change of groundwater level in this area.At the same time,the key driving factors of groundwater level change in the four geomorphic units are different.The key driving factors of groundwater level change in Bashang Blateau are total vegetable output,output value of the first and third industries and effective irrigation area.The key driving factors of Chaixuan Basin are the total output of pig,cattle and sheep meat,the output of the first,second and third industries and the total output of vegetables;Zhuohuai Basin is the output of the first,second and third industries,the total output of pig,cattle and sheep meat,the total population at the end of the year and the total output of vegetables;Yuyang basin is the total output of pig,cattle and sheep meat,the output of the first,second and third industries,the total population at the end of the year and the total output of vegetables.(4)According to the prediction effect of groundwater level change model,four geomorphic units of Bashang Plateau,Chaixuan Basin,Zhuowai Basin and Yuyang Basin in Zhangjiakou area are established by using regression principle.The multiple correlation coefficient R is 0.991,0.994,0.961 and 0.993 respectively,and the determination coefficient R~2is 0.983,0.988,0.924 and 0.985 respectively,which shows that each model enters the regression equation 98.3%,98.8%,92.4%and 98.5%of the variation of groundwater level can be explained by the variables of 0.001,respectively,and the p-values all reach the significant level of 0.001,and the relative errors of the models are within 4.5%,respectively0-4.34%,0.06%-2.82%,0.59%-1.14%and 0.33%-4.43%.The average relative errors were within 2.5%,which were 1.57%,1.33%,0.83%and 2.26%respectively.Therefore,the simulation accuracy of the model is high,which shows the correlation and driving effect between various natural factors,human factors and the change of groundwater level.(5)According to the prediction results of groundwater level change model,if the growth rate of natural factors and socio-economic factors data in 2015 of four geomorphic units in Zhangjiakou compared with the corresponding data in 2010 is used as scenario for simulation,it can be seen from the analysis of groundwater level changes of four geomorphic units in 2020,2025 and 2030 under different scenarios,the prediction values of groundwater level in Bashang Blateau are 9.28-10.33m,11.69-15.26m and 15.34-24.44m,respectively,which are 1.9-2.95m,4.31-7.88m and 7.96-17.06m compared with that in 2015;the prediction values of groundwater level in Chaixuan Basin are 51-54.45m,57.89-67.85m and67.11-88.81m respectively,which are 3.3-6.75m,10.19-20.15m and 19.41-41.11m compared with that in 2015;The prediction values of groundwater level in Zhuohuai Basin are25.44-26.99m,28.9-34.02m and 34.03-46.67m respectively,which are 2.58-4.13m,6.04-11.16m and 11.17-23.81m compared with that in 2015;the prediction values of groundwater level in Yuyang Basin are 0.18-0.36m,11.15-11.64m and 9.82-11.13m respectively,which are 2.58-4.13m,0.53-1.02m and 1.04-2.35m compared with that in 2015.The results show that according to the current economic development situation in Zhangjiakou area,the groundwater level in Chaixuan Basin,Zhuohuai Basin and Yuyang Basin will continue to decline without increasing the efforts of rational control and management of groundwater resources,among which the groundwater level in Chaixuan Basin is the most serious,and the groundwater level in the Bashang Blateau will resume to rise.The research results of this paper can provide theoretical guidance for the rational utilization and protection of groundwater resources,the sustainable development of social economy and the construction of ecological civilization in Zhangjiakou area,and have important significance for the water conservation,sustainable utilization and rational allocation of water resources in Beijing Tianjin Hebei areas in china. |
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