An overview of precipitation isotopes over the Extensive Hexi Region in NW China

Until now, most studies of the isotopic composition of precipitation in the Extensive Hexi Region have described individual sites. A systematic study considering the regional atmospheric circulation, the complex topography, and the re-evaporation process is lacking. This paper compares and summarizes previous studies in the Extensive Hexi Region, to provide a regional picture of the characteristics of isotopic composition of precipitation and moisture sources. δ 18O and δD values exhibit significant seasonal variability, with higher values in summer and lower values in winter due to the seasonality of temperature and moisture sources. The temperature effect is more pronounced in the Extensive Hexi Region than in northwest China. The altitude effects are also evident with a gradient of −0.23 ‰/100 m for δ 18O and −1.67 ‰/100 m for δD. But, the d-excess increases gradually with altitude, and the higher d-excess values occur at mountain sampling sites which are attributed to the difference of the secondary evaporation between mountains and plain. Finally, the moisture source in the study area was investigated, and the results show relatively complex patterns: the westerly and polar air masses dominate in winter; however, there are inconsistent results in summer. Whether or not the westerly air mass is the dominant supply of moisture in summer is yet to be determined. Additionally, in the course of reviewing and integrating, some new research questions are identified for future work.