降水产流同位素径流分割研究进展与展望

降水产流是陆地水循环中大气降水补给地表水的重要环节。氢氧稳定同位素的指纹效应能够有效示踪径流的补给来源、路径和地理区域。同位素径流分割模型已从二元分割逐渐发展到三元乃至多元分割模型，多学科交叉也逐渐丰富了径流分割研究的方法体系。本文对同位素径流分割在降水产流中的应用进展作了总结分析，介绍了环境同位素（²H和¹⁸O）在降水产流研究中的应用现状、存在的不确定性以及处理误差的方法和应用特点。最后对环境同位素在径流分割领域的应用前景进行了论述，提出环境同位素结合GIS、InSAR、ERT等地球物理方法，将进一步深化流域水文要素时空变化的研究。

Research progress and prospects of isotopic hydrograph separation in rainfall-runoff generation

Background, aim, and scope Rainfall runoff is an important part of the replenishment of surface water in the terrestrial water cycle. Over the past few decades, global patterns and rainfall extremes have been altered by climate change, which has significantly affected the regional hydrological cycle, especially rainfall-runoff events. Extreme rainfall-runoff events have become more frequent, resulting in a series of flood and landslide disasters. Separating the sources of water in extreme runoff is crucially important for understanding the mechanisms of storm runoff generation. Currently, environmental isotopes, e.g., stable isotopes of hydrogen and oxygen, are useful tools in tracing the water sources of surface runoff, while there are still many problems that should be further discussed. This paper aims to review the advancements and shortcomings of the isotopic hydrograph separation method and provide prospects and suggestions for this research field. Materials and methods We focused on the basic principle of hydrogen and oxygen stable isotope tracing. The deficiencies of isotope hydrograph separation of runoff sources were summarized based on theoretical advances and bibliometric methods in this study, and we explored the application prospects of environmental isotopes in runoff source separation. Results We showed that (1) the binary mixed model has difficulty reflecting the real contribution of water sources to stream runoff, especially during rainstorm processes, while the ternary mixed model can be used to effectively divide the contribution ratios of each water source. (2) Isotope fractionation is a major cause of errors in identifying the water sources of stream runoff. In large watersheds, uncertainties will significantly increase, which makes it difficult to control research errors. (3) Errors on a time scale can be handled by models such as VWA, CMW, and RunCE, but the calculation range is expanded in the VWA method, and the risk of subjective judgment errors exists in the CMW method. In contrast, the RunCE model can be used to effectively reduce the deviation of ice and snow melt at a given time scale. Discussion The theory of the binary mixed model is the basis for isotope runoff separation. Although there are many restrictive conditions, this is the beginning of introducing isotope tracer technology into the field of hydrograph separation, which lays a solid foundation for the development of isotope runoff separation. Great progress has been made using the ternary mixed model, which is based on the binary mixed model. The combination of multiple tracers has not only achieved theoretical breakthroughs but also meets the needs of dealing with complex environmental variables. It is possible to solve the problem of isotope runoff separation based on the existing theories. However, the focus of isotope runoff separation research is still on the quantification of uncertainty. The spatial variability of tracers can be accurately reflected using the Gaussian error analysis approach, yet it is challenging to assess errors driven by isotope fractionation effects. The MCMC method, based on Bayesian theory, is used to estimate the uncertainty of parameters, which is an effective means to improve the reliability of isotope runoff separation results. The errors caused by the time-history changes in precipitation and ice and snow meltwater at various stages can be rectified by using the weighted average method and the RunCE method, respectively. Conclusions It is difficult to thoroughly assess deviations in the runoff separation process using the error analysis method of isotope hydrograph separation. The precise separation of the runoff components depends on insight into the direction in which the error occurs and the effective selection of methods for quantifying uncertainty. Recommendations and perspectives The isotope tracing technique is anticipated to offer an exact analysis of the recharge relationship of water resources, while the geophysical approach is an effective way to comprehend the character of the macro hydrological distribution. Therefore, it is necessary to combine isotope runoff separation with geophysical methods such as GIS, InSAR, and ERT to effectively evaluate the hydrological cycle of a watershed. The isotope hydrograph separation of runoff source development trends will be interdisciplinary and complementary in the future.