Examining the impacts of estimated precipitation isotope (δ18O) inputs on distributed tracer-aided hydrological modelling

Other literature type English OPEN
Delavau, Carly J. ; Stadnyk, Tricia ; Holmes, Tegan (2016)

Tracer-aided hydrological models are becoming increasingly popular tools as they have documented utility in constraining model parameter space during calibration, reducing model uncertainty, and assisting with selection of appropriate model structures. However, the issue of data availability, particularly input data, proves to be a major challenge associated with this type of application. Tracer-aided hydrological modelling typically requires a time series of isotopes in precipitation (<i>&delta;</i><sup>18</sup>O<sub>ppt</sub>) to drive model simulations, but unfortunately, throughout much of the world, and particularly in sparsely populated high-latitude regions, these data are not widely available. This study uses the isoWATFLOOD tracer-aided hydrological model to investigate the usefulness of three types of estimated <i>&delta;</i><sup>18</sup>O<sub>ppt</sub> for model input, and the impact that these data have on model simulations and parameterization in the remote Fort Simpson Basin, NWT, Canada. This study showed that although total simulated streamflow was not significantly impacted by choice of <i>&delta;</i><sup>18</sup>O<sub>ppt</sub> input, isotopes in streamflow (<i>&delta;</i><sup>18</sup>O<sub>SF</sub>) simulations and the internal apportionment of water (and therefore, model parameterizations) were impacted, particularly during large precipitation and snowmelt events. This finding highlighted the importance of estimated <i>&delta;</i><sup>18</sup>O<sub>ppt</sub> to capture both the variability and seasonality in precipitation isotopes as critical for tracer-aided hydrological modelling, especially when precipitation events displayed distinctly different isotopic compositions than that of streamflow. This study achieves an understanding of how isoWATFLOOD can be used in regions with a limited number of <i>&delta;</i><sup>18</sup>O<sub>ppt</sub> observations, and that the model can be of value in such regions. This study reinforces that a tracer-aided modelling approach assists with resolving hydrograph component contributions, and works towards diagnosing the issue of model equifinality.
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