气候异常对临汾盆地地下水系统的影响

Influences of Climatic Anomaly on the Groundwater System in Linfen Basin

利用数值模拟方法研究了气候异常对临汾盆地地下水系统的影响。在介绍临汾盆地水文地质条件的基础上,运用地下水模拟软件GMS建立了研究区潜水和中层承压水的水流模型,并根据地下水实测水位资料对模型进行了识别和验证。通过对临汾盆地近50年降水量的分析,确定将连续出现两个特殊干旱年(降水频率为95%)作为气候异常变化情形,运用建立的数值模型对气候异常条件下地下水水位的变化进行了模拟,结果表明:气候异常条件下潜水水位将下降0.3～0.9m,承压水水位将下降2.5～5m。承压水目前是本区地下水的主要开采对象,异常条件下承压水水位的下降可能会使该地区地面沉降进一步加剧。研究降水量异常变化对临汾盆地地下水资源的影响对于该区域水资源的开发利用和规划管理等方面具有重要的现实意义。

Climatic fluctuation can exert a considerable impact on the groundwater circulation. Based on a case study in Linfen Basin, the impacts of climatic change on groundwater circulation are assessed. The study area is located in the middle and lower reaches of the Yellow River basin, and the total area of the basin is approximately 4686 km2. The groundwater floor in the study area can be divided into three aquifers, which are phreatic aquifer, middle confined aquifer and deep confined aquifer. The phreatic aquifer and the middle confined aquifer are the main targets of exploitation, so the water level changes in response to climatic anomaly in these two aquifers are focused on in this paper. To start with, balance analysis of the groundwater resources is carried out. The groundwater recharge process includes precipitation infiltration, surface water leakage and lateral recharge, while the groundwater discharge process includes evaporation and artificial exploitation. The climatic anomaly can be identified by the appearance of two extra drought periods when the annual rainfall of the last 50 years is analyzed. Then, the groundwater level change under extraordinary climate is estimated by the numerical simulation. According to the hydro-geological conditions of Linfen basin, the numerical model of the phreatic aquifer and the confined aquifer is constructed with GMS. Also, the model is calibrated by the data of monitored groundwater levels. Repeatedly computing reduces 70.9 percent of the error ranges between simulated and monitored water level of the phreatic aquifer below 0.5 meter, and that of the confined aquifer below 1 meter. The simulation results prove that the calibrated model can reflect the actual hydro-geological conditions, so it can represent the actual water level changes. Therefore, the change of the groundwater level under climatic anomaly is simulated by the calibrated numerical model. According to the simulation results, the groundwater level of the phreatic aquifer may fall by 0.3 to 0.9 meter, and that of the confined aquifer may fall 2.5 to 5 meters in response to climatic anomaly. The continuous and intensive exploitation of groundwater has caused many problems in Linfen basin, such as groundwater level declining, surface subsidence, and land crack. The sharp decline of groundwater level under climatic anomaly can exacerbate the land subsidence. It is suggested that the local government should be prepared to deal with climatic anomaly to prevent the water shortage and ground water floor degradation.