Hydrograph separation is a fundamental catchment descriptor,revealing information about sources of water in runoff generation processes. The water isotopes are ideal tracers in studying hydrological processes since the isotope fractionation produces a natural labeling effect within the hydrologic cycle. The water isotope technique has become one of effective means for investigating complex hydrologic system on a catchment scale. This paper reviews the progress on the use of stable water isotope techniques in catchment hydrograph separation in last decades. Also,the isotope mixing model for hydrograph separation and its uncertainties are explained in detail. In future research,there are three hot issues in the use of isotopic hydrograph separation（ IHS） ： integrating new approaches into IHS,calibration and verification of IHS model and IHS application in large river basins.
Hydrogen and oxygen isotopes in precipitation have been widely used as effective traces to investigate hydrological processes such as evaporation and atmospheric moisture source. This study analyzed δD and δ^(18)O of precipitation in continuous event-based samples at three stations of Pailugou Catchment from November 2012 to December 2013. The δ^(18)O and δD values ranged from-32.32‰ to +3.23‰ and from-254.46‰ to +12.11‰, respectively. Results show that the δ^(18)O displayed a distinct seasonal variation, with enriched values occurring in summer and relatively depleted values in winter, respectively. There was a statistically significant positive correlation between the δ^(18)O and δD values and local surface air temperature at all the three stations. The nearest Global Network of Isotopes in Precipitation(GNIP) station(Zhangye), compared to the Meteoric Water Lines for this study, showed the obvious local evaporation effects with lower intercept and slope. Additionally, d-excess(δD- 8δ^(18)O) parameter in precipitation exhibited an anti-phase seasonal variability with the δ^(18)O. The 96-h back trajectories for each precipitation event using Hybrid Single Particle Lagrangian Integrated Trajectory(HYSPLIT) model indicated a dominant effect of westerly air masses in summer and the integrated influence of westerly and polar air masses in winter.
