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| Titel |
Actual evapotranspiration and precipitation measured by lysimeters: a comparison with eddy covariance and tipping bucket |
| VerfasserIn |
S. Gebler, H.-J. Hendricks Franssen, T. Pütz, H. Post, M. Schmidt, H. Vereecken |
| 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 ; 19, no. 5 ; Nr. 19, no. 5 (2015-05-05), S.2145-2161 |
| Datensatznummer |
250120703
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| Publikation (Nr.) |
 copernicus.org/hess-19-2145-2015.pdf |
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| Zusammenfassung |
| This study compares actual evapotranspiration (ETa) measurements by a
set of six weighable lysimeters, ETa estimates obtained with the eddy
covariance (EC) method, and evapotranspiration calculated with the full-form
Penman–Monteith equation (ETPM) for the Rollesbroich site in the Eifel
(western Germany). The comparison of ETa measured by EC (including
correction of the energy balance deficit) and by lysimeters is rarely
reported in the literature and allows more insight into the performance of both
methods. An evaluation of ETa for the two methods for the year 2012
shows a good agreement with a total difference of 3.8% (19 mm) between
the ETa estimates. The highest agreement and smallest relative
differences (< 8%) on a monthly basis between both methods are
found in summer. ETa was close to ETPM, indicating that ET was
energy limited and not limited by water availability. ETa differences
between lysimeter and EC were mainly related to differences in grass height
caused by harvest and the EC footprint. The lysimeter data were also used to
estimate precipitation amounts in combination with a filter algorithm for the
high-precision lysimeters recently introduced by Peters et al. (2014). The
estimated precipitation amounts from the lysimeter data differ significantly
from precipitation amounts recorded with a standard rain gauge at the
Rollesbroich test site. For the complete year 2012 the lysimeter records
show a 16 % higher precipitation amount than the tipping bucket. After a
correction of the tipping bucket measurements by the method of Richter
(1995) this amount was reduced to 3%. With the help of an on-site camera
the precipitation measurements of the lysimeters were analyzed in more
detail. It was found that the lysimeters record more precipitation than the
tipping bucket, in part related to the detection of rime and dew, which
contribute 17% to the yearly difference between both methods. In
addition, fog and drizzle explain an additional 5.5% of the total
difference. Larger differences are also recorded for snow and sleet
situations. During snowfall, the tipping bucket device underestimated
precipitation severely, and these situations contributed also 7.9% to the
total difference. However, 36% of the total yearly difference was
associated with snow cover without apparent snowfall, and under these
conditions snow bridges and snow drift seem to explain the strong
overestimation of precipitation by the lysimeter. The remaining
precipitation difference (about 33%) could not be explained and did not
show a clear relation to wind speed. The variation of the individual
lysimeters devices compared to the lysimeter mean are small, showing
variations up to 3% for precipitation and 8% for evapotranspiration. |
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