Hydrological changes prints in subarctic watersheds discharge records: a case study in the Duke River watershed, Yukon, Canada.

Abstract:

Hydrological changes from alpine glacierized watersheds have been reported from almost all the regions of the world. In most cases those changes have, or are foreseen to have, marked impacts on water resources with implications for downstream population and ecosystems. One of the ways to assess climate change impacts on glacierized watersheds is to conduct appropriate statistical analyses on historical hydrometric data where long and accurate time series exist.

In the Yukon, Canada, a fair number of hydrometric time series are made accessible by institutions such as Environment Canada or the Yukon National Parks Organisation. Some of those time series have been studied previously at a regional scale in the territory. In the present study, focusing on the Duke River watershed area, we reanalyse these datasets based on a larger number of discharge characteristics and compare results with regional meteorological data analysis. We perform non-parametric trend analysis to assess long-term changes in watersheds response to climate-induced variability.

Eight watersheds with varying glacierized area were chosen for this study. Main glaciers in the region are situated in St. Elias Mountains and are characterised by ubiquitous mass loss (Arendt et al., 2002; Barrand and Sharp, 2010). Historical hydrometric data analysis shows two distinct hydrological regimes in the area: (i) – snow fed rivers with peak runoff following spring snowmelt, and (ii) – glacier fed rivers with peak runoff following glacier ablation in July. While total discharge during ablation season does not vary significantly between watersheds with different regimes, the difference in late summer runoff is close to 50%.

Moreover, trend analysis provides evidence of changes in hydrological regimes in the area. As a response to ubiquitous temperature increase, hydrologically active period for highly glacieized watershed (with glacierized area of 30%) has shifted from the beginning of August to the beginning of July in the course of the last 39 years.

Results of trend analysis also show increase in winter and early spring low flows for almost all watersheds. This can be attributed to changes of ground freezing/thawing timing, and thus reflects changes in ground water contribution to watershed runoff as a response to observed trends in climatic forcing.