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| Titel |
The Plynlimon water balance 1969-1995: the impact of forest and moorland vegetation on evaporation and streamflow in upland catchments |
| VerfasserIn |
J. A. Hudson, S. B. Crane, J. R. Blackie |
| 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 ; 1, no. 3 ; Nr. 1, no. 3, S.409-427 |
| Datensatznummer |
250000186
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| Publikation (Nr.) |
 copernicus.org/hess-1-409-1997.pdf |
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| Zusammenfassung |
The Plynlimon experiment in mid-Wales, designed to
determine the extent to which coniferous plantation increases evaporation
losses and reduces streamflow relative to upland grassland, has now been
yielding data since 1969 from the grassland Wye and the 67% forested Severn
catchments. Water balance analyses of the early data indicated significantly
higher evaporation rates from the forested catchment and studies of the
hydrological processes involved attributed this to the high loss rates
of precipitation intercepted by the forest canopy. Models based on these
process studies predicted losses from the forested catchment that were
similar but marginally higher than those determined by the catchment water
balance.
As the data sets from the catchments increased in length and a
detailed reassessment of the ratings of the streamflow gauging structures
was completed the updated water balances continued to show a significantly
greater evaporation loss from the forested catchment, but the gap between
the forest water balance and the model predictions widened. Furthermore
Hudson and Gilman (1993), using the best data sets then available, identified
downward trends in the evaporation from both catchments which the models
did not reproduce and for which no obvious physical or physiological explanation
was forthcoming.
This dictated a major reassessment of the longer data
sets, using the more powerful data processing techniques now available,
to identify and eliminate any errors and inconsistencies. This paper describes
the reassessment of the precipitation data and the estimates of potential
evaporation and presents the water balance results emerging from the revised
data sets.
The revised results indicate that the evaporation losses from
the grassland Wye catchment remained broadly similar to the potential evaporation
estimates throughout the 1969-1995 period. The losses from the forested
area of the Severn catchment declined from a level some 61% above that
of the grassland in 1972 to a level only 18% higher before the start of
felling in 1985. This downward trend continued as the felling and re-planting
progressed. Over the period since 1990 the forest catchment losses
appear to have stabilised at some 5-10% below those of the grassland
catchment.
Using the revised precipitation and potential evaporation data,
process based models over-predict the forest catchment evaporation throughout
the period and do not mirror the re-felling decline. Possible reasons for
this apparent decline in evaporation rates are discussed. |
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