Impacts of a Rapidly Declining Mountain Snowpack on Streamflow Timing in Canada's Fraser River Basin.

Do Hyuk Kang,Xiaogang Shi,Siraj Ul Islam,Huilin Gao,Stephen J Déry

doi:10.1038/srep19299

Do Hyuk Kang, Xiaogang Shi + Show 3 more

Open Access

https://doi.org/10.1038/srep19299

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Abstract

With its headwaters in the water towers of the western Cordillera of North America, the Fraser River is one of the continent’s mightiest rivers by annual flows, supplies vital freshwater resources to populous downstream locations, and sustains the world’s largest stocks of sockeye salmon along with four other salmon species. Here we show the Variable Infiltration Capacity (VIC) model’s ability to reproduce accurately observed trends in daily streamflow for the Fraser River’s main stem and six of its major tributaries over 1949-2006 when air temperatures rose by 1.4 °C while annual precipitation amounts remained stable. Rapidly declining mountain snowpacks and earlier melt onsets result in a 10-day advance of the Fraser River’s spring freshet with subsequent reductions in summer flows when up-river salmon migrations occur. Identification of the sub-basins driving the Fraser River’s most significant changes provides a measure of seasonal predictability of future floods or droughts in a changing climate.

Highlights

While trends in streamflow timing are commonly used as indicators of climate change[13], identifying the driving factors for observed changes remain quite challenging[14]
The six sub-basins examined in the present study contribute 75.0% (67.9%) of the annual observed Fraser River discharge at Hope, British Columbia (BC) with the largest contributions from the Thompson-Nicola (TN), Upper Fraser (UF) and Quesnel (QU) sub-basins (Table 1)
The Variable Infiltration Capacity (VIC) model accurately simulates trends in daily streamflow observed across the FRB, with Nash-Sutcliffe Efficiency (NSE) scores between 0.47 and 0.97, statistically significant correlations and relatively low measures of error (Table 2)

Summary

Introduction

While trends in streamflow timing are commonly used as indicators of climate change[13], identifying the driving factors for observed changes remain quite challenging[14]. This paper addresses three key research goals: 1) to evaluate the performance of a semi-distributed, macroscale hydrological model in simulating FRB observed streamflow trends at a daily timescale; 2) to quantify the relative contribution and its change over time of the FRB’s main sub-basins to total streamflow on the main-stem lower Fraser River; and 3) to assess the impacts of rising air temperatures, of changes in precipitation types and amounts, and of rapidly declining mountain snowpacks on changes in streamflow timing and amounts across the FRB. Both observational and modelling datasets are applied to investigate changes to the hydrologic regime of the FRB from 1949 to 2006

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Conclusion