Multi-scale assessment of environmental changes impact on subarctic glacierized watersheds hydrology

Abstract

Subarctic glacierized catchments are complex hydrological systems of paramount importance not only for water resources management but also for various ecosystem services. They are environmentally fragile and exert a high sensitivity to changes in climatic forcing. Several studies indicated the hydrological importance of the non-glacierized portions of these watersheds by illustrating the potential water storage capacity and runoff production of their proglacial areas. However, on a watershed scale, the hydrological role of every single component other than glaciers is not yet well understood. I hypothesized that subarctic proglacial areas play an important role in the glacierized watersheds hydrology and that glacier retreat does not entirely define their hydrological response to climate change. Hence, to accurately project the response of subarctic glacierized catchments to environmental changes, it is necessary to better understand and quantify the contribution of each hydrological component in runoff production. The primary objective of this project is thus to improve the knowledge necessary to project the impact of environmental changes on the hydrology of subarctic regions by (i) isolating and quantifying the role of shrinking glaciers in recent hydrological changes in the southwestern Yukon as well as estimating future hydrological changes in the region, (ii) disentangling the importance of various hydrological components to the total summer runoff in the headwaters of a subarctic glacierized watershed, and (iii) analyzing the genesis of icings to obtain new insights into the generation of winter baseflow and winter hydrological processes in the headwaters of subarctic glacierized watersheds of different complexity. To achieve these objectives, three summer field campaigns in a glacierized watershed of the St. Elias Mountains, Yukon, Canada, were conducted. The data collected were complemented with laboratory activities, statistical analyses, and remote sensing. Due to the high hydrological complexity met in such environments, a multi-technique approach based on the use of natural tracers, hydro-meteorological monitoring and time lapse imagery was applied in the field site to understand hydrological processes within the proglacial areas. This project confirms that glacier retreat, even if shown to be of primary importance, cannot explain all the hydrological changes in the study region. Whereas increases in yearly and ablation season discharge, decreases in flow variability and changes in ablation season start are characteristics of watersheds with a dominant glacier runoff, increase in winter discharge magnitude and shifts in its timing were observed in all the watersheds independently on their hydrological regime. In the headwaters of a watershed which passed peak water, this project also illustrates the hydrological role of subarctic proglacial field on a watershed scale. In particular, the findings demonstrate that hydrological components such as talus slope tributaries and, possibly, runoff from areas with buried ice contribute significantly to runoff production. It was also found that the contributing sources of the ablation season seem to be active in winter as well, hence highlighting the importance of the proglacial field for the hydrology of the headwaters during both seasons. The results of this project propose that, to understand the hydrological changes taking place in subarctic mountainous environments, more attention should be given to the headwaters of glacierized watersheds without focusing only on glaciers’ contribution. Instead, future research should focus on identifying the role of specific hydrological features and components, such as areas with buried ice and talus slopes, on a watershed scale. Finally, it demonstrates the importance of working towards incorporating the important hydrological components identified in this study in conceptual and numerical hydrological models.

Date	1 May 2020
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Michel Baraër (Supervisor)