Abstract: Background, aim, and scope Due to the global warming, the regional climate and hydrological processes are undergoing the major changes, the surface water vapor pressure in the northwest arid region is closely related to the water vapor content and precipitation. The water vapor is the most active component in the global water cycle processes. It is of great significance to grasp the facts and laws of water vapor pressure change for understanding the regional water circulation process and its response to the global change. However, the recording history of the instrumental data is too short to be used in the study of long-time scale climate change. The tree rings have an incomparable advantages in the study of past climate change in the arid areas. This study is intended to provide the research data of tree rings in the Dongda Mountain of Hexi Corridor, the facts of regional climate change are revealed, the basic data are provided for understanding the causes of climate change in the northwestern China, and the scientific reference is provided for the utilization of water resources in the arid areas. Materials and methods The total 66 sample cores of 39 Picea crassifolia were collected in the Dongda Mountain nature reserve of Hexi Corridor (39°00′—39°04′N, 100°45′—100°51′E) in April 2012. After the sample core is air-dried, the cross dating is carried out and the width chronology is established, the quality of dating is inspected by use of the COFECHA program. On the basis of the exact dating, the 4—5 sample cores with wider rings and fewer missing rings are selected for stripping year by year. The stripped sample is moved to the filter tube for the organic solvent extraction; subsequently, the sodium hypochlorite and acetic acid are used to remove the lignin; the sodium hydroxide solution is used to remove the hemicellulose; finally, the samples is homogenized by the ultrasonic cell crushing apparatus, and then it is dried and preserved after the freeze-drying in vacuum, so the α-cellulose is obtained. The cellulose samples is packaged into the sample by a silver capsule year by year, and then the Delta V Advantage stable isotope mass spectrometer is used to connect the high-temperature pyrolysis element analyzer (TC/EA) to determine the δ18O value, and the δ18O chronology sequence of tree ring is established. The meteorological data apply the Zhangye meteorological station data closest to the sampling point and the CRU3.10 grid points (38°—40°N, 99°—101°E) data information. The correlation coefficient between the tree ring δ18O chronological table and the water vapor pressure is calculated, and the transformation equation between the tree ring δ18O and the water vapor pressure has been established by using the linear regression model. The spatial correlation between the reconstructed sequence and the grid data is calculated through the web site at http://climexp.knmi.nl/. Results The water vapor pressure of the Dongda Mountain in July and August has a good correlation with the tree ring δ18O chronology sequence, with the correlation coefficient reaches -0.643 (p < 0.001), and the change sequence of average water vapor pressure at the Dongda Mountain in July to August from 1807 to 2011 has been reconstructed, the variance interpretation of the reconstructed equation reaches 41.4%. The segmented examination indicates that the result of reconstruction of vapor pressure is stable and reliable. Discussion In the reconstruction 205 a, there are 6 stages with the larger water vapor pressure, which respectively is 1844—1858, 1869—1923, 1935—1941, 1954—1963, 1972—1978 and 2003—2007, and 7 stages with smaller water vapor pressure, which respectively is 1807—1843, 1859—1868, 1924—1934, 1942—1953, 1964—1971, 1979—2002 and 2007—2011. The accuracy of the sequence reconstructed by this paper has been further proved by the comparative analysis of the reconstructed sequence of water vapor pressure, the reconstructed sequence of precipitation in the surrounding tree rings and the historical drought events. Conclusions the drought in early 19th century and early 21st century is a widespread drought period in Mongolia, Inner Mongolia and Xinjiang and so on. The reconstruction results have a good synchronism with the dry and wet changes recorded by the tree ring in the surrounding area, and have a good response with the historically recorded of drought extreme events. The spatial correlation analysis has shown that the water vapor in the study area mainly comes from the monsoon water vapor, and is accompanied by the water vapor transport in the westerly belt, and the reconstruction results have the certain regional representativeness. Recommendations and perspectives The north of the Dongda Mountain is the Badain Jaran Desert, and the south side is the middle section of Hexi Corridor, so the long-time scale climate difference between both the north and south sides can further studied and analyzed.
Keywords: tree-ring δ18O; water vapor pressure reconstruction; Dongda Mountain; Picea crassifolia