[1] Changes in air temperature, precipitation, and, in some cases, glacial runoff affect the timing of river flow in watersheds of western Canada. We present a method to detect streamflow phase shifts in pluvial, nival, and glacial rivers. The Kendall-Theil robust lines yield monotonic trends in normalized sequent 5-day means of runoff in nine river basins of western Canada over the period . In comparison to trends in the timing of the date of annual peak flow and the center of volume, two other less robust metrics often used to infer streamflow timing changes, our approach reveals more detailed structure on the nature of these changes. For instance, our trend analyses reveal extension of the warm hydrological season in nival and glacial rivers of western Canada. This feature is marked by an earlier onset of the spring melt, decreases in summer streamflow, and a delay in the onset of enhanced autumn flows. Our method provides information on streamflow timing changes throughout the entire hydrological year, enhancing results from previous methods to assess climate change impacts on the hydrological cycle.

Climatic and hydrologic variations between the decades 1976-1985 and 1986-95 are examined at 210 climate stations for temperature,2Tl climate stations for precipitation, and 642 hydrology stations from across Canada. The variations in climate are distributed across a broad spatial area. Temperatures were generally warmer in the more recent decade, with many stations showing significant increases during spring and fall. Significant decreases in temperature were found during winter in eastern Canada. Significant increases in temperature were more frequent in western Canada than in the east. Significant decreases in precipitation were also more prevalent in the north, as were increases in the south, except for Ontario and Quebec where little or no change has taken place. The hydrologic responses to these variations in climate are classified into four hydrograph types and six patterns of shifts in streamflow between the two decades. The 642 hydrologic stations fall into pr6cipitations dtaient dgalement plus courantes dans le Nord, tout comme l'6taient Ies hausses dans le Sud, sauf en Ontario et au Qudbec, oil l'on a enregistrd que tEnvironment Canada, Vancouver, BC

Abstract:The Pacific Decadal Oscillation (PDO) is a large-scale climate system feature that influences the surface climate and hydrology of western North America. In this paper, we review the literature describing the PDO and demonstrate its effects on temperature, precipitation, snowfall, glacier mass balance, and streamflow with a focus on western Canada, and particularly British Columbia. We review how the PDO index was developed and discuss other North Pacific climate patterns that resemble the PDO. The impacts of PDO on glacier mass balance and streamflow from retrospective studies are also reviewed and illustrated with specific examples from BC. We assess the current state of knowledge regarding the PDO and provide a critical assessment of its use in hydroclimatology. This information should provide insight on the sensitivity of projects to climatic variability.

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Concern over the potential impact of anthropogenic climate change on flooding has led to a proliferation of studies examining past flood trends. Many studies have analysed annual-maximum flow trends but few have quantified changes in major (25-100 year return period) floods, i.e. those that have the greatest societal impacts. Existing major-flood studies used a limited number of very large catchments affected to varying degrees by alterations such as reservoirs and urbanisation. In the current study, trends in majorflood occurrence from 1961 to 2010 and from 1931 to 2010 were assessed using a very large dataset (>1200 gauges) of diverse catchments from North America and Europe; only minimally altered catchments were used, to focus on climate-driven changes rather than changes due to catchment alterations. Trend testing of major floods was based on counting the number of exceedances of a given flood threshold within a group of gauges. Evidence for significant trends varied between groups of gauges that were defined by catchment size, location, climate, flood threshold and period of record, indicating that generalizations about flood trends across large domains or a diversity of catchment types are ungrounded. Overall, the number of significant trends in major-flood occurrence across North America and Europe was approximately the number expected due to chance alone. Changes over time in the occurrence of major floods were dominated by multidecadal variability rather than by long-term trends. There were more than three times as many significant relationships between major-flood occurrence and the Atlantic Multidecadal Oscillation than significant long-term trends.

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Abstract:The Georgia Basin-Puget Sound Lowland region of British Columbia (Canada) and Washington State (USA) presents a crucial test in environmental management due to its combination of abundant salmonid habitat, rapid population growth and urbanization, and multiple national jurisdictions. It is also hydrologically complex and heterogeneous, containing at least three streamflow regimes: pluvial (rainfall-driven winter freshet), nival (melt-driven summer freshet), and hybrid (both winter and summer freshets), reflecting differing elevation ranges within various watersheds. We performed bootstrapped composite analyses of river discharge, air temperature, and precipitation data to assess El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) impacts upon annual hydrometeorological cycles across the study area. Canadian and American data were employed from a total of 21 hydrometric and four meteorological stations. The surface meteorological anomalies showed strong regional coherence. In contrast, the seasonal impacts of coherent modes of Pacific circulation variability were found to be fundamentally different between streamflow regimes. Thus, ENSO and PDO effects can vary from one stream to the next within this region, albeit in a systematic way. Furthermore, watershed glacial cover appeared to complicate such relationships locally; and an additional annual streamflow regime was identified that exhibits climatically driven non-linear phase transitions. The spatial heterogeneity of seasonal flow responses to climatic variability may have substantial implications to catchment-specific management and planning of water resources and hydroelectric power generation, and it may also have ecological consequences due to the matching or phase-locking of lotic and riparian biological activity and life cycles to the seasonal cycle. The results add to a growing body of literature suggesting that assessments of the streamflow impacts of ocean-atmosphere circulation modes must accommodate local hydrological characteristics and dynamics.