Evaluating the effects of climate change on river water temperature downstream of a hydropower reservoir in western Canada

Abstract

This paper evaluates the impact of climate change on the water temperature of the Nechako River near the town of Vanderhoof (British Columbia, Canada). To do so, the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) hydraulic and water temperature model was used with data from 10 climate models representing two Shared Socioeconomic Pathways (SSP 2-4.5 and SSP 5-8.5) over two future time periods (2041-2070 and 2071-2100). The results showed an upward trend in projected water temperatures for all tested discharge rates from the impounding reservoir during the warmest periods of the year. The study found that water temperatures are expected to increase by up to 2.57 °C for the near future (2041-2070) and up to 3.56 °C on average for all flow scenarios studied for a far future (2071-2100) when using SSP5-8.5. The timing of the peak water temperature during the summer is also expected to shift, with maximum water temperatures occurring up to 10 days later than in the reference period. In 10.3% of the far future SSP5-8.5 scenarios, at least one day per summer had a mean daily temperature of at least 24 °C, which exceeds limits of 20 °C for sockeye salmon and 21 °C for white sturgeon which are considered detrimental for the fish. It has been shown that over 50% of sockeye salmon will stop their sustained swimming at water temperatures of 24 °C due to cardiac limitations.

Résumé

Cette publication évalue l’impact des changements climatiques sur la température de l’eau de la rivière Nechako près de la ville de Vanderhoof (Colombie-Britannique, Canada). Pour ce faire, le modèle hydraulique et thermique du Hydrologic Engineering Center’s River Analysis System (HEC-RAS) a été utilisé conjointement aux données de 10 modèles climatiques représentant deux trajectoires socio-économiques partagées (SSP 2-4.5 et SSP 5-8.5) couvrant deux horizons futurs (2041-2070 et 2071-2100). Les résultats démontrent une tendance ascendante de la température des eaux pour tous les scénarii de débits étudiés provenant du réservoir en amont durant la période la plus chaude de l’année. Il est attendu que la température de l’eau augmente autant que 2.57  °C pour le futur rapproché (2041-2070) et jusqu’à 3.56 °C pour le futur lointain (2071-2100) pour le scénario SSP 5-8.5. Les températures de pointes se déplaceront aussi et seront retardées d’environ 10 jours comparativement à la période de référence. Dans 10.3% des cas étudiés pour le scénario du futur lointain de SSP 5-8.5, la température de l’eau excède 24  °C au moins une journée par été, ce qui dépasse largement les limites de 20 °C pour le saumon rouge et 21  °C pour l’esturgeon blanc, limites considérées nuisibles à la santé de ces poissons. Il a été démontré que plus de 50% des saumons rouges arrêteront leur nage prolongée lorsque l’eau atteint le seuil des 24  °C en raison des limitations cardiaques.

Keywords:

• Climate change
• water temperature
• hydraulic modelling
• thermal modelling
• HEC-RAS

Acknowledgements

The authors would like to thank Rio Tinto for sharing their HEC-RAS hydraulic model implementation on the Nechako River and associated data (https://riotinto-nechakofacts.herokuapp.com/). The results of this study incorporate modified Copernicus Climate Change Service information from 2020. The European Commission and ECMWF are not responsible for any use that may be made of the Copernicus information or data contained within this paper.

This paper uses the ERA5 reanalysis dataset produced by Hersbach, H. et al. (2018), which was downloaded from the Copernicus Climate Change Service (C3S) Climate Data Store: https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-single-levels?tab = overview.

The base map in Figure 1 was created using ArcGIS® software by Esri. ArcGIS® and ArcMap™ are the intellectual property of Esri and are used herein under license. Copyright © Esri. All rights reserved. For more information about Esri® software, please visit www.esri.com.

The authors would like to acknowledge the World Climate Research Program, which coordinated and promoted CMIP6 through its Working Group on Coupled Modelling. We would also like to thank the climate modeling groups for producing and making their model output available, the Earth System Grid Federation (ESGF) for archiving the data and providing access, and the various funding agencies that support CMIP6 and ESGF.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author, PG, upon reasonable request.