Abstract: As natural tracers, the stable hydrogen and oxygen isotope compositions in precipitation are sensitive to global and local environmental changes. The existing modern observations improve the understanding of precipitation isotopes, but the connections between annual, seasonal and diurnal timescales are still not very clear for many regions. The isotope-equipped general circulation model (GCM) provides an effective method to acquire the long-term time series of precipitation isotope compositions, although the accuracy should be examined before being applied to specific locations. Here the stable water isotopes in precipitation simulated by the isoGSM2 are assessed at 12 sites in a valley city, Lanzhou, in western China, and then the simulations are used to examine the annual, seasonal and diurnal variations in precipitation isotopes from 1979 to 2020. According to the observations across this city, the isoGSM2 simulations are good at describing the isotope variability in precipitation. On the annual scale, δ18O in precipitation fluctuates periodically, which may be closely related to large-scale climate periodic change. On the seasonal or monthly scale, the 18O in precipitation is enriched in spring and summer and depleted in autumn and winter. Under various time scales, the δ18O in the daytime is higher than that at night. The temporal variation of δ18O in the daytime and nighttime is the similar as that in the whole day, and the δ18O in the daytime and nighttime is the close in June, July, December and January.
 

precipitation,stable isotope,general circulation model