Uncertainty Analysis of the Tracer-Based Hydrograph Separation Method

Tracer-based hydrograph separation relying on the mass balance equations of water and isotopic compositions is very appealing and widely used in basin hydrology, due to its simplicity. However, much uncertainty of this method is presented in practical applications, which is mainly affected by model assumptions. In this paper, theoretical analysis is conducted to test the reality of some fundamental assumptions involved in isotopic hydrograph separation method. The results indicate that soil water plays an important role in stormflow generation, and the previous assumption that contributions from soil water are negligible in hydrograph separation seems to be unrealistic. It shows that the bigger the contribution rate of soil water is, or the greater the difference of the isotopic compositions of soil water and base flow is, and thus the bigger the estimated error of the proportion of pre-event water is. Finally, some feasible suggestions are put forward to improve the application of the isotopic hydrograph separation method.