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| Titel |
Methods for snowmelt forecasting in upland Britain |
| VerfasserIn |
R. J. Moore, V. A. Bell, R. M. Austin, R. J. Harding |
| 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 ; 3, no. 2 ; Nr. 3, no. 2, S.233-246 |
| Datensatznummer |
250000912
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| Publikation (Nr.) |
 copernicus.org/hess-3-233-1999.pdf |
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| Zusammenfassung |
| Snow, whilst not a dominant feature of Britain's maritime climate, can exert
a significant influence on major floods through its contribution as snowmelt.
Flood warning systems which fail to take account of melting snow can prove
highly misleading. Selected results of a study on methods for improved snowmelt
forecasting using trail catchments in upland Britain are presented here. Melt
models considered range from a temperature excess formulation, with the option
to include wind and rain heating effects, to a full energy budget melt
formulation. Storage of melt in the pack is controlled by a store with two
outlets, allowing slow release of water followed by rapid release once a
critical liquid water content is reached. For shallow snow packs, a partial
cover curve determines the proportion of the catchment over which snow extends.
The melt, storage and release mechanisms together constitute the PACK snowmelt
module which provides inputs to the catchment model. Either a lumped or
distributed catchment model can be used, configured to receive snowmelt inputs
from elevation zones within the catchment; a PACK snowmelt module operates
independently within each zone and its inputs are controlled by appropriate
elevation lapse rates. Measurements of snow depth and/or water equivalent, from
snow cores or a snow pillow, are assimilated to correct for a lack of direct
snowfall measurements needed to maintain a water balance during snowfall. The
updating scheme involves operating a PACK module at the measurement site (the
"point model") in parallel to PACK modules in the catchment model,
with point model errors being transferred using a proportioning scheme to adjust
the snowpack water contents of the catchment model. The results of the
assessment of different model variants broadly favour the simpler model
formulations. Hourly automatic monitoring of water equivalent using the snow
pillow can help in updating the model but preferential melting from the pillow
can be a problem. The energy budget melt formulation proves useful in
understanding the energy components of melt typical of upland Britain. It
reveals that, during the main melt phase, melt can occur in almost equal measure
by sensible heat exchange and by latent heat of condensation, as warm air near
saturation in cloud condenses on the snowpack; net radiation makes a negligible
contribution. This provides a physical explanation for the success of the simple
temperature excess approach to snowmelt estimation. |
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