Groundwater temperature variation characteristics and main influence factors identification in Zhangye Basin of northwest China

Groundwater temperatures regime is an important content in groundwater regimes.Changes in groundwater temperatures reflect not only the source and composition of groundwater recharge,but also the intensity of groundwater recharge,and to some extent reflecting the close degree between the change of groundwater resources and groundwater recharge areas' climate change.It can be used as an important scientific basis for groundwater resources evaluation.Groundwater temperatures are closely related with recharge area's meteorological and hydrological conditions in northwest arid region of China.In this paper,we take Zhangye basin as study area,on the basis of groundwater temperature dynamic variation characteristics research and identification of the relationship of the mountain areas and basin's precipitation,air temperature,duration of sunshine and mountainous runoff with groundwater temperature,we use grey correlation analysis method to identify the main influence factors of groundwater temperature of different buried conditions(shallow groundwater and confined groundwater).According to this we can provide a scientific basis for the recharge sources of the basin groundwater.The study shows that: The shallow groundwater and the confined groundwater decreased by 0.78 ℃ and 1.17 ℃ respectively in the study area from 1990 to 2009.The mountainous runoff has the maximum correlation with the groundwater temperature.Its grey correlation coefficients are up to 0.82(shallow groundwater temperature) and 0.81(confined groundwater temperature).The second one is basin's precipitation and their grey correlation coefficient with groundwater temperature is up to 0.73(both shallow groundwater and confined groundwater).The third one is mountainous precipitation and its grey correlation coefficient with groundwater temperature is up to 0.72(shallow groundwater) and 0.73(confined groundwater).The rising of air temperature in mountain area has no obvious effect on the basin groundwater temperature.In addition,the increasing of groundwater exploitation and Heihe water transfer lead the shallow groundwater and confined groundwater temperature nearly to the same trends in study area.Annual groundwater temperature changes slowly,and it difficult to be aware of this reason.But the groundwater temperature change can bring a lot of environmental geology problems,so the research of groundwater temperature change regime must be put much attention in the future.