| Xi’an is the largest city in northwest China. As the rapid development of economy, thegroundwater in Xi’an was exploited excessively and its level was on a sharp decline between1970s and1990s, while led to a series of environmental and geological problems whichseriously affected the healthy development of the city. On the basis of relevanthydrogeological information in Xi’an, this paper studied the effects of climate change andhuman activities on groundwater levels and analyzed the spatial and temporal variation ofgroundwater buried depth between1984and2010, as well as made a prediction ofgroundwater buried depth from2011to2020and evaluated water supply safety degree of thewater resource areas. The main conclusions are drawn as follows:1、 According to the analysis of groundwater buried depth, the average depth ofgroundwater in study area between1984and2010was11.72m, with the maximum drop5.92m. It mainly went through3phases: rapid decline phase, stable phase, slow reboundphase; the confined water head dropped noticeably before1997, with the general declineabout50m and the maximum decline up to100m. However, there is a obvious rebound in theself-supply wells area, with the maximum rebound up to3.3m/a.2、Based on the groundwater buried depth variation in different areas received by thetime series analysis method, the groundwater level in western suburbs of Fenghe and Zaohewater source area (K83-3fu) and city self-supply wells (291) mutated in2003and2006respectively, the average buried depth of groundwater began to rebound; while thegroundwater level in northern suburbs of Weibin mutated in1996, the buried depth showed astriking decline between1997and2010, but the groundwater levels in other areas was notprone to a sudden change. Furthermore, buried depth of groundwater in agriculturalirrigation area and Bahe water source area were sensitive to environmental changes and theirfluctuation were greater than the first and second terrace areas.3、 The groundwater buried depth area divided by the Kriging interpolation methodindicate that buried depth in southeast was deeper than it in north and confined water head inexploitation areas were obviously deeper than that of other areas. Meanwhile, based on thestatistics of MapGis attribute database, studied the changes of area of groundwater buried depth and confined water head, the buried depth were mainly between10m and20m, theproportion of the area increased from45.9%to56.8%; area with the buried depth of confinedwater head over100m shrank, the buried depth from20m to60m and from60m to100mexpanded, the buried depths mainly were between20m and60m, which accounted for50%ofthe total area.4、 By using of principle component projection-clustering model, differenthydrogeological units and exploitation areas of xi’an a were divided into four groundwaterlevel dynamic types: hydrological strong, middle or weak type and mining influence. Andthen combined with the hydrometeorological factors, water depth analysis and principalcomponent analysis, a conclusion was made that the influence by hydrological factorsrange from flood land to the second terrace dive was gradually weak. The impact ofhydrometeorological factors descending order was runoff＞precipitation＞evaporation＞temperature and other factors, groundwater in exploitation areas was heavily affected byexploitation.5、 Based on the regression model，this paper studied the relationship between industrialactivities and groundwater buried depth, the industrial activities in1990s had a noticeableimpact on buried depth, each additional1billion industrial output would lead to a decrease of0.2m in average buried depth of water table.6、 An ANFIS neural network prediction model considering the affecting factors such asprecipitation, evaporation, and the amount groundwater exploitation was established, thencombined with the GM (1,1) and the RBF neural networks the average groundwater levelchanges from2011to2020in Xi’an was predicted. The results showed that the averagegroundwater buried depth fluctuates around12.5m, and the overall trend was on a slight rise.7、 The problems of groundwater water supply in the study area was analyzed based onon-site investigation. Reference the relevant research results in other areas, the evaluationindex system of water supply security was established. Finally evaluated the security ofgroundwater supply of5groundwater source areas by hierarchy-set pair analysis, the result ofsecurity degree of groundwater supply ranking in the order of superiority was：Zaohegroundwater resource field＞Weihe western suburbs groundwater resource field＞Weibingroundwater resource field＞Fenghe groundwater resource field＞Bahe groundwater resource field. |
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