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Comparative statistical hydroclimatology of glacial and nival rivers in southwest Yukon and northwest British Columbia Fleming, Sean William

Abstract

A diverse suite of nonparametric statistical and time series analysis techniques was applied to historical streamflow data from five glacier-fed and four snowmelt-fed rivers in the southwest Canadian subarctic, in order to determine whether, and if so, how the two fluvial regimes respond differently to variability in climatic forcing. Four types of streamflow variability dynamics, corresponding to four timescales of climatic forcing, were considered. Methodological development was also performed as appropriate. Results were as follows. At the seasonal level, the annual hydrographs of glacial and nival rivers differed in virtually every aspect of their flow magnitude and timing. Glacial rivers exhibited higher water resource productivity throughout the year and an extended freshet, and glacial cover was of similar importance to basin scale in determining annual hydrologic cycle amplitude, probably reflecting negative mass balance trends. High-frequency interannual streamflow fluctuations were then corifirmed to be strongly attenuated by watershed glacierization, but the effect was statistically significant only for robust metrics of freshet flow and timing and overall yearly flow magnitude. The dampening mechanism responsible appears restricted to variability timescales of roughly two years or less, consistent with separate analyses of lower-frequency behaviour. Glacial and nival rivers in the study area were then demonstrated to exhibit selective teleconnectivity to the Arctic Oscillation and El Nino-Southern Oscillation, respectively, from a net annual water resource perspective; this reflects a broader decoupling of glacial and nival yearly discharge anomalies. Seasonal responses were more complex. At the longest timescale considered, presence or absence of watershed glacierization was shown to control whether rivers here grew larger or smaller, respectively, in response to historically-observed climatic changes. Progressive shifts in annual hydrograph form were also observed and linked to glacierization. The results were in all cases readily physically interpretable, underscored the dramatic impacts of glacierization upon water resource variability, and strongly confirmed and extended existing understanding of glacial-nival hydroclirnatologic contrasts. In particular, this is the first study to examine the comparative hydroclimatology of glacial and nival rivers at a broad range of variability timescales using a single dataset, affording a more comprehensive view of such watershed dynamical processes.

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