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Based on the precipitation samples collected in Minxian in the western Loess Plateau from 2019 to 2021, this study analyzes the influence of moisture sources on precipitation isotopes. Through the specific humidity correction of the backward trajectory, it is found that Xinjiang and the middle and lower reaches of the Yangtze River may be the main moisture sources. Through cluster analysis of backward trajectories, it is found that in the summer half-year, the water vapor from the east and northeast leads to the precipitation with a depleted isotope ratio, while the water vapor from the south and northwest leads to the precipitation with an enriched isotope ratio; in the winter half, water vapor from the east leads to precipitation with enriched isotope ratios, while water vapor from the northwest and northeast leads to precipitation with depleted isotope ratios. In addition, the precipitation isotope values showed a tendency to deplete with the duration of water vapor transport in the summer half-year, but this tendency was not obvious in the winter half-year. The relationship between precipitation isotopes and water vapor transport height showed a positive correlation in both the winter half-year and summer half-year. Using the Potential Source Contribution Factor analysis methods and the backward trajectory after the specific humidity revision, it was found that the potential evaporation source areas in the summer half-year are larger in extent, mainly distributed in the eastern and southern regions of the sampling site, and the contribution of local recycled vapor to precipitation is 32.17%; while the potential evaporation source areas in the winter half-year are smaller in extent, they are only distributed in the southern region of the sampling site, and the contribution of local recycled vapor to precipitation is 24.66%. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the atmospheric water cycle in Lanzhou and surrounding areas, a place sensitive to climatic conditions and located in the vertex of the 'Monsoon Triangle' of China; this study obtained 243 event-based precipitation samples from four stations in Lanzhou, Yongdeng, Yuzhong and Gaolan for 1 year from April 2011 to March 2012. The seasonal variations of δO and d excess indicate that westerly water vapor, local moisture and summer monsoon all have an influence in this region on a large scale. The westerlies play a dominant role. However, the impact of monsoon moisture has a seasonal limitation, mainly during the period from June to early August. On a local scale, the transportation of moisture appears via two routes. The contribution rate of recycling moisture, over the region, is only 3.6 % on average due to the deficiency of water resource in arid and semi-arid land. Additionally, the effect of secondary evaporation has also been discussed, and the results show that relative humidity, temperature and precipitation amount have different impacts on the effect. However, the influence of precipitation amount is not obvious when the rainfall amount is below 10 mm, while the meteorological parameters of relative humidity and temperature play a significant role in that scope. [ABSTRACT FROM AUTHOR]

Deuterium excess and stable oxygen isotopes in precipitation have been widely applied to trace the source of water vapor. In this study, hydrogen and oxygen isotope analyses of samples were collected on seven sampling stations in Dingxi area from April 2019 to April 2020. The seasonal variation of hydrogen and oxygen stable isotopes as well as the d-excess indicate that the source of water vapor in Dingxi area is mostly from a single source. However, there are different sources of water vapor in the summer. Meanwhile, water vapor sources were analyzed using the Lagrange algorithm, indicating two different principal water vapor sources for precipitation in the area: some locally recycled water vapor in summer and autumn, and most water vapor from the westerly belt. Further studies using the PSCF and CWT analysis methods show that the locally recycled water vapor contributes more to its precipitation in the northwest of Dingxi area. [ABSTRACT FROM AUTHOR]

The proportional contribution of recycled moisture to local precipitation is a geographically dependent parameter that cannot be ignored in water budgets. Stable hydrogen and oxygen isotopes are sensitive to environmental changes and can be applied to investigate the modern water cycle. In this study, a three-component mixing model is used to calculate the contribution of different water vapors (advection, evaporation and transpiration) to summer precipitation in Lanzhou city, Northwest China. The results show that for all sampling sites in Lanzhou, the contribution of advection vapor to precipitation is the largest, followed by the plant transpiration vapor, and the contribution of surface evaporation water vapor is usually the least, with the average values of 87.96%, 9.1% and 2.9%, respectively. The spatial differences of plant transpiration vapor are generally larger than those of advection vapor and surface evaporation vapor, and the high values appear in Yongdeng, Daheng and Gaolan. [ABSTRACT FROM AUTHOR]

The deuterium excess (d) in precipitation, determined by the stable hydrogen and oxygen isotopes (δ2H and δ18O), is a widely applied parameter in tracing the water vapor source. Based on the multiple-year observations of stable water isotopes in precipitation at four stations in the Lanzhou city, Northwest China, we analyzed the variations in deuterium excess in precipitation at the Asian monsoon margin region. The mean value of deuterium excess at the study region is 11.0‰ in the dry season and 8.0‰ in the wet season. The d value in precipitation negatively correlates with air temperature and vapor pressure. The low d value during the wet season reflects the monsoon moisture transported from long distances. During the dry season, the continental air masses correspond to the higher d value in precipitation. The moisture regimes based on reanalysis data are generally consistent with the findings using a stable isotopic approach, and the monsoon moisture is highlighted in summer precipitation at these monsoon margin sites. [ABSTRACT FROM AUTHOR]