摘要:  Under the increasing pressure of water shortage and steppe degradation, information on the hydrological cycle in steppe region
in Inner Mongolia, China is urgently needed. An intensive investigation of the temporal variations of δD and δ18O in precipitation was
conducted in 2007–2008 in the Xilin River Basin, Inner Mongolia in the northern China. The δD and δ18O values for 54 precipitation
samples range from +1.1‰ to –34.7‰ and –3.0‰ to –269‰, respectively. This wide range indicates that stable isotopes in
precipitation are primarily controlled by different condensation mechanisms as a function of air temperature and varying sources of vapor.
The relationship between δD and δ18O defined a well constrained line given by , which is nearly identical to the Meteoric Water Line in
the northern China. The temperature effect is clearly displayed in this area. The results of backward trajectory of each precipitation day
show that the vapor of the precipitation in cold season (October to March) mainly originates from the west while the moisture source is
more complicated in warm season (April to September). A light precipitation amount effect existes at the precipitation event scale in this
area. The vapor source of precipitation with higher d-excesses are mainly from the west wind or neighboring inland area and precipitation
with lower d-excesses from a monsoon source from the southeastern China .