Model Based Spatial Distribution of Oxygen-18 Isotopes in Precipitation Across Canada

Abstract

Challenges inherent in mesoscale (large domain) hydrologic modelling of remote ungauged basins include validation of model results and quantification of uncertainty in the predictions. Isotope equipped hydrological models, such as isoWATFLOOD, have the ability to simulate both quantity and isotopic composition of streamflow and runoff generation processes providing more options for model validation, but first require information about isotopic composition of precipitation across the model domain. The stable water isotopic composition of precipitation (18OPPT) is available from stations sampling monthly composite precipitation, but the data are spatially and temporally discontinuous, particularly in northern areas of Canada. Here we use new data from the Canadian Network for Isotopes in Precipitation (CNIP) to create and evaluate a variety of empirical relationships to develop improved interpolations of the spatial distribution of 18OPPT across Canada. The goal of this research is to develop 18OPPT prediction models that can be incorporated directly within the isoWATFLOOD hydrological modelling framework to provide spatially variant 18OPPT patterns as forcing data for the iso-hydrological model. Comparison of model results has identified models capable of simulating annual 18OPPT distributions, but also identified seasons and areas where the geographical and climatological parameters included in this analysis were not able to simulate the measured distributions. Spring, summer and fall model results were satisfactory; however, winter model results were more variable, indicating increased complexity in the driving forces of 18OPPT patterns during this season. Overall, model results improve with the addition of time-variant climate parameters, this finding being especially significant during the winter. Improving the precipitation input fields within isotope-equipped hydrological models will provide a valuable tool for water use management within large, remote, and often ungauged Canadian rivers and will facilitate studies of both climate variability and surface hydrology in remote regions.

Les dfis inhrents la modlisation hydrologique chelle moyenne (mso-chelle) des bassins non jaugs loigns englobent la validation des rsultats de modle et la quantification de l'incertitude lie aux prdictions. Les modles hydrologiques et isotopiques, par exemple le modle isoWATFLOOD, ont la capacit de simuler la fois la quantit et la composition isotopique des processus de gnration du dbit et de l'coulement, ce qui offre davantage d'options pour la validation de modle. Cependant, ils exigent d'abord des donnes l'gard de la composition isotopique des prcipitations dans l'ensemble du domaine modlis. La composition en isotopes stables des prcipitations (d18OPPT) est disponible partir de stations procdant l'chantillonnage de composites mensuelles. Toutefois, les donnes sont discontinues sur les plans spatial et temporel, en particulier dans les rgions nordiques du Canada. Ici nous utilisons de nouvelles donnes tires du CNIP, c'est--dire le Canadian Network for Isotopes in Precipitation (Rseau canadien pour les isotopes dans les prcipitations), afin de crer et d'valuer diverses relations empiriques dans le but de concevoir de meilleures interpolations de la distribution spatiale des d18OPPT l'chelle du Canada. L'objectif de la recherche consiste laborer des modles de prdiction des d18OPPT pouvant tre intgrs directement au cadre de modlisation hydrologique isoWATFLOOD afin de fournir des tendances des d18OPPT spatialement variables en tant que donnes de forage pour le modle d'observation hydro-isotopique. La comparaison des rsultats de modle a permis d'identifier des modles capables de simuler les distributions annuelles de d18OPPT. Cependant, elle a galement permis de cerner des saisons et des rgions o les paramtres gographiques et climatologiques inclus dans l'analyse ne permettaient pas de simuler les distributions mesures. Les rsultats de modle au printemps, en t et l'automne se sont avrs satisfaisants. Toutefois, les rsultats de modle obtenus en hiver taient plus variables, ce qui indique une complexit accrue des facteurs dterminants des tendances des d18OPPT au cours de cette saison. Dans l'ensemble, les rsultats de modle s'amliorent avec l'ajout de paramtres du climat variables dans le temps, cette constatation tant d'une importance toute particulire au cours de l'hiver. L'amlioration des champs de saisie des donnes de prcipitations dans les modles d'hydrologie isotopique fournira un outil prcieux pour la gestion de l'utilisation de l'eau des rivires canadiennes de grande importance, loignes et souvent non jauges et elle facilitera en outre les tudes de la variabilit climatique et de l'hydrologie de surface dans les rgions loignes.

Acknowledgements

The authors would like to thank all of the reviewers who provided their comments and insight, helping to improve this paper. This research has benefited from discussions with Dr. John Gibson, Dr. Yi Yi, and Dr. Tom Edwards. This research was funded by a University of Manitoba Graduate Scholarship, a Natural Sciences and Engineering Research Council of Canada (NSERC) Canada Graduate Scholarship, and Alberta Innovates-Technology Futures. Additional gratitude is expressed to the Canadian Network for Isotopes in Precipitation for providing the updated isotopes in precipitation data necessary to conduct this research.