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| Titel |
Winter stream temperature in the rain-on-snow zone of the Pacific Northwest: influences of hillslope runoff and transient snow cover |
| VerfasserIn |
J. A. Leach, R. D. Moore |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 2 ; Nr. 18, no. 2 (2014-02-27), S.819-838 |
| Datensatznummer |
250120293
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| Publikation (Nr.) |
 copernicus.org/hess-18-819-2014.pdf |
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| Zusammenfassung |
| Stream temperature dynamics during winter are less well studied than
summer thermal regimes, but the winter season thermal regime can be
critical for fish growth and development in coastal catchments. The
winter thermal regimes of Pacific Northwest headwater streams, which
provide vital winter habitat for salmonids and their food sources, may
be particularly sensitive to changes in climate because they can
remain ice-free throughout the year and are often located in
rain-on-snow zones. This study examined winter stream temperature
patterns and controls in small headwater catchments within the
rain-on-snow zone at the Malcolm Knapp Research Forest, near
Vancouver, British Columbia, Canada. Two hypotheses were addressed by
this study: (1) winter stream temperatures are primarily controlled by
advective fluxes associated with runoff processes and (2) stream
temperatures should be depressed during rain-on-snow events, compared
to rain-on-bare-ground events, due to the cooling effect of rain passing
through the snowpack prior to infiltrating the soil or being delivered
to the stream as saturation-excess overland flow. A reach-scale energy
budget analysis of two winter seasons revealed that the advective
energy input associated with hillslope runoff overwhelms vertical energy
exchanges (net radiation, sensible and latent heat fluxes, bed heat
conduction, and stream friction) and hyporheic energy fluxes during rain and rain-on-snow
events. Historical stream temperature data and modelled snowpack
dynamics were used to explore the influence of transient snow cover on
stream temperature over 13 winters. When snow was not present, daily
stream temperature during winter rain events tended to increase with
increasing air temperature. However, when snow was present, stream
temperature was capped at about 5 °C, regardless of
air temperature. The stream energy budget modelling and historical
analysis support both of our hypotheses. A key implication is that
climatic warming may generate higher winter stream temperatures in the
rain-on-snow zone due to both increased rain temperature and reduced
cooling effect of snow cover. |
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