Development of an innovative coupled isotope-hydrologic model for large Canadian watersheds

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Recent recognition of non-stationarity in climate, and consequently hydrology, is requiring more advanced watershed models to project changes in future runoff and the impacts to Canada’s water supply and therefore security. In Canada, much of the water resides at high latitudes where watershed modelling capabilities and accuracies are hindered by sparse hydro-meteorological networks, with densities below World Metrological Organization minimum gauging network standards. This research endeavours to develop improved hydrologic prediction tools for northern Canadian regimes through an innovative coupled isotope-hydrometric approach. Coupled isotope-discharge measurement has proven particularly useful in tracing progressive downstream hydrologic change related to climate or land-use non-stationarity. Isotopes are also useful diagnostic variables in constraining hydrologic model parameter ranges, but have typically been applied ad-hoc only when and where observational data is available. The proposed program focuses on innovation and development of the isoWATFLOOD model, a fully distributed hydrological model that simulates and routes water isotopes across regional landscapes. Key innovations of the isoWATFLOOD model are proposed to enhance applicability to high-latitude, remote basins by incorporating snow and snowmelt dynamics and the deuterium isotope for evaporation modelling and evapotranspiration partitioning. Simulation of the isotope tracers provides a means to validate internal hydrologic process contributions to streamflow, improving the realism of simulated hydrographs and ensuring proper hydroclimatic feedbacks. Continuous simulation of both isotopes also has the advantage of ‘gap-filling’ observed isotope records in large river basins, and the potential for isotope signal projection under future climates. The model will be tested in two pan-arctic Canadian basins with existing isotope datasets (Mackenize and lower Nelson Rivers). Theoretical (simulated) isotope frameworks will be produced to validate evaporation and evapotranspiration partitioning. Improved simulation of snowmelt dynamics will significantly improve annual water balance simulations since snowmelt represents the largest flow volume on an annual basis for these basins. Research will provide new tools and HQP with specialized training in hydrologic simulation, with the goal of improving simulation in large rivers without additional field instrumentation. Sectors requiring streamflow projection for infrastructure design, planning, and construction in the North, and recertification of dam structures will be impacted as estimates of extreme flow events are required but no longer represented by gauged records. Outcomes are intended for Canadian researchers and water practitioners requiring advanced tools to assist in streamflow projection under climate change.