A conceptual hydrological model that links the Xin'anjiang hydrological model and a physically based snow energy and mass balance model, described as the XINSNOBAL model, was developed in this study for simulating rain-on-snow events that commonly occur in the Pacific Northwest of the United States. The resultant model was applied to the Lookout Creek Watershed in the H. J. Andrews Experimental Forest in the western Cascade Mountains of Oregon, and its ability to simulate streamflow was evaluated. The simulation was conducted at 24-hour and one-hour time scales for the period of 1996 to 2005. The results indicated that runoff and peak discharge could be underestimated if snowpack accumulation and snowmelt under rain-on-snow conditions were not taken into account. The average deterministic coefficient of the hourly model in streamflow simulation in the calibration stage was 0.837, which was significantly improved over the value of 0.762 when the Xin'anjiang model was used alone. Good simulation performance of the XINSNOBAL model in the WS10 catchment, using the calibrated parameter of the Lookout Creek Watershed for proxy-basin testing, demonstrates that transplanting model parameters between similar watersheds can provide a useful tool for discharge forecasting in ungauged basins.
Isotopic fractionation is the basis of tracing the water cycle using hydrogen and oxygen isotopes.Isotopic fractionation factors in water evaporating from free water bodies are mainly affected by temperature and relative humidity,and vary significantly with these atmospheric factors over the course of a day.The evaporation rate (E) can reveal the effects of atmospheric factors.Therefore,there should be a certain functional relationship between isotopic fractionation factors and E.An average isotopic fractionation factor (α*) was defined to describe isotopic differences between vapor and liquid phases in evaporation with time intervals of days.The relationship between α* and E based on the isotopic mass balance was investigated through an evaporation pan experiment with no inflow.The experimental results showed that the isotopic compositions of residual water were more enriched with time;α* was affected by air temperature,relative humidity,and other atmospheric factors,and had a strong functional relation with E.The values of α* can be easily calculated with the known values of E,the initial volume of water in the pan,and isotopic compositions of residual water.
Tao WANGWei-min BAOHai-li XUZhen ZHUSi-min QUPeng SHIHai-ying HURui-qi FANQian LI
