 |
| Titel |
Evaluating the reliability of point estimates of wetland reference evaporation |
| VerfasserIn |
H. Gavin, C. T. Agnew |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1027-5606
|
| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 7, no. 1 ; Nr. 7, no. 1, S.3-10 |
| Datensatznummer |
250004415
|
| Publikation (Nr.) |
 copernicus.org/hess-7-3-2003.pdf |
|
|
|
|
|
| Zusammenfassung |
| The Penman-Monteith formulation of evaporation has been criticised for its
reliance upon point estimates so that areal estimates of wetland evaporation based upon
single weather stations may be misleading. Typically, wetlands comprise a complex mosaic
of land cover types from each of which evaporative rates may differ. The need to account
for wetland patches when monitoring hydrological fluxes has been noted. This paper presents
work carried out over a wet grassland in Southern England. The significance of fetch on
actual evaporation was examined using the approach adopted by Gash (1986) based upon
surface roughness to estimate the fraction of evaporation sensed from a specified distance
upwind of the monitoring station. This theoretical analysis (assuming near-neutral
conditions) reveals that the fraction of evaporation contributed by the surrounding area
increases steadily to a value of 77% at a distance of 224 m and thereafter declines
rapidly. Thus, point climate observations may not reflect surface conditions at greater
distances. This result was tested through the deployment of four weather stations on the
wetland. The resultant data suggested that homogeneous conditions prevailed so that the
central weather station provided reliable areal estimates of reference evaporation during
the observation period March–April 1999. This may be a result of not accounting for high
wind speeds and roughness found in wetlands that lead to widespread atmospheric mixing.
It should be noted this analysis was based upon data collected during the period
March-April when wind direction was constant (westerly) and the land surface was moist.
There could be more variation at other times of the year that would lead to greater
heterogeneity in actual evaporation.
Keywords: evaporation, Penman-Monteith, automatic weather station, fetch, wetland |
| |
|
| Teil von |
|
|
|
|
|
|
|
|