Variation Characteristics And Mechanism Of Groundwater Response To Climate Change In Zhangye Basin

Based on hydrological cycle theory, this thesis is themed with variation characteristics and mechanism of groundwater response to climate change in Zhangye Basin. Using hydrogeology, geostatistics, and gray theory of mathematics methods and spatial analysis techniques of MapGIS, and combining qualitative judgments and quantitative analysis together, firstly, systematic analyzing and coupling the years of monitoring data of key elements like precipitation, temperature, runoff, groundwater table and temperature which comes from upstream of Qilian Mountains areas and plain areas, including site visit and overall thorough research of climate, hydrology, topography, regional geological structure, formation lithology, groundwater embedment features and water resources development in study area, and identifying the main factors that affect the groundwater change in Zhangye Basin and its intra-annual and inter-annual variation. Then, quantitative analyzed the impact characteristics that how the climate change in upstream of Qilian Mountains impact the groundwater recharge source structure and recharge amount in Zhangye Basin. Also identified the characteristic of intra-annual and inter-annual variation of water cycle process that affected by human activities in Zhangye Basin. Finally, the non-uniformity characteristic and mechanism that the groundwater of Zhangye Basin responded to the climate change were discussed. According to the discussion results, rational utilization and conservation measures of groundwater in Zhangye Basin under different climate conditions were proposed.Main achievements and creative cognitions as follows:(1)The climate of study area is transforming from cold-dry to warm-wet, and the precipitation of Qilian Mountain area is the main infection factors of mountainous runoff and the groundwater recharge of Zhangye Basin.The multi-year average temperature are -0.95℃(Qilian Mountain area) and 7.59℃(Zhangye Basin) respectively. The multi-year average precipitations are 408.67 mm/a (Qilian Mountain area) and 118.12 mm/a (Zhangye Basin) respectively. Annual temperature and precipitation fluctuated greatly, and regional climate change is closely related with it. There is a wavelike rises trend of temperature in study area. Since 1960s, the temperature of Qilian Mountain area has risen 1.48℃and the temperature of Zhangye Basin has risen 1.33℃. Temperature increase on April and October are the largest contribution rate of annual temperature increase in those areas. Since 1990s, the temperature rising rate is significantly increased. Since 1990s, it has a significant increase in precipitation of Qilian Mountain area. The precipitation of Qilian Mountain area has increased from 311.85 mm/a (1991) to 502.60 mm/a (2009), and the average increase rate is 10.60 mm/a. Precipitation increase on July and August are the largest contribution rate of annual precipitation increase. As the annual precipitation is less than 150 mm in arid Zhangye Basin, so the reason of its groundwater table rising is the increase of precipitation in Qilian Mountain area.The mountainous runoff is significantly correlated with precipitation of Qilian Mountain area, and its bilateral Pearson correlation coefficient is up to 0.845 with significance of the 0.01 confidence level. The mountainous runoff is not significantly correlated with the temperature of Qilian Mountain area, and its bilateral Pearson correlation coefficient is just about 0.306 with significance of the 0.05 confidence level. It shows that, the precipitation of Qilian Mountain area is the main influencing factors of mountainous runoff. Because the mountainous runoff is the main recharge source of the groundwater of Zhangye Basin and the mountainous runoff accounting for more than 80% of the total recharge, so, according to the linear regression model between precipitation of Qilian Mountain and mountainous runoff, if didn't consider the temperature and human activities impact, when the precipitation of Qilian Mountain is greater than 125 mm/a and increase 10 mm/a, the mountainous runoff increase 0.40×108m3/a, and the groundwater recharge increase 0.34×108m3/a.(2) The groundwater of Zhangye Basin response to climate change of Qilian Mountain area has a lag-continuity characteristic.The maximum shallow groundwater temperature is lagging behind the temperature and precipitation (both in Qilian Mountain area and Zhangye Basin) for 2 months, and the maximum confined groundwater temperature is lagging behind for 3 months. The climate of Qilian Mountain area has a significant influence on groundwater of Zhangye Basin with a lag-continuity characteristic. Under the condition of extreme drought and extreme wet, its affection on groundwater of Zhangye Basin can last for 2-3 years, and the confined groundwater of Zhangye Basin has a more obvious response to climate change of Qilian Mountain area(3) The groundwater of Zhangye Basin response to climate change and human activities has non-uniformity characteristic.During the year 1984 to 2009, the shallow groundwater table and confined groundwater head had declined in different degrees. The decrease amplitude of confined groundwater head was more than shallow groundwater table, and there was a great difference of groundwater table change amplitude in space. Farther from the river, greater of the groundwater table decline; closer to the river, smaller of the groundwater table decline. Conversely, closer to the river, greater of the groundwater table rising; farther from the river, smaller of the groundwater table rising. Because far from the river belt, the southeast clinoplain of Zhangye Basin has a maximum groundwater table decline. Near the Heihe mainstream area, the groundwater table decline smaller.The groundwater buried condition of Zhangye Basin, topography and geomorphology and surface runoff condition are the basis of non-uniformity characteristic that the groundwater responses to the climate change, and the climate change and human activities are the motivations. The decrease of river water infiltration and the construction of reservoirs lead to the continuously decrease of groundwater table of the southeast clinoplain of Zhangye Basin. The implementation of Heihe water transfer project and the increasing of precipitation of Qilian Mountain area in recent years lead to increase of river water infiltration which was the main reason of groundwater table rising at the southeast clinoplain of Zhangye Basin.(4) Following the periodic variation law of climate change in Qilian Mountain area, target and timely regulate the groundwater exploitation intensity are beneficial to groundwater conservation and sustainable use of water resources.The mountainous runoff of Qilian Mountain area is the main recharge source of groundwater of Zhangye Basin, so it should follow the laws of climate periodic variation regularity and based on different partitions groundwater buried conditions and recharge conditions, adjust intensity of groundwater exploitation timely and conserve groundwater reasonably. Broaden the sources of income and reduce expenditure simultaneously. Pay attention to the regulation and storage capacity of the Gobi zone of piedmont, increasing groundwater recharge storage in the wet season artificially and strengthening groundwater exploitation in shallow-buried zones in order to capture shallow groundwater invalid evaporation and prevent soil salinization.