Drexler, Judy Z. and Snyder, Richard L. and Spano, Donatella Emma Ignazia and Paw U, Kyaw Tha (2004) *A Review of models and micrometeorological methods used to estimate wetland evapotranspiration.* Hydrological Processes, Vol. 18 (11), p. 2071-2101. eISSN 1099-1085. Article.

Full text not available from this repository.

DOI: 10.1002/hyp.1462

## Abstract

Within the past decade or so, the accuracy of evapotranspiration (*ET*) estimates has improved due to new and increasingly sophisticated methods. Yet despite a plethora of choices concerning methods, estimation of wetland *ET* remains insufficiently characterized due to the complexity of surface characteristics and the diversity of wetland types. In this review, we present models and micrometeorological methods that have been used to estimate wetland *ET* and discuss their suitability for particular wetland types. Hydrological, soil monitoring and lysimetric methods to determine *ET* are not discussed.
Our review shows that, due to the variability and complexity of wetlands, there is no single approach that is the best for estimating wetland *ET*. Furthermore, there is no single foolproof method to obtain an accurate, independent measure of wetland *ET*. Because all of the methods reviewed, with the exception of eddy covariance and LIDAR, require measurements of net radiation (*R*_{n}) and soil heat flux (*G*), highly accurate measurements of these energy components are key to improving measurements of wetland *ET*.
Many of the major methods used to determine *ET* can be applied successfully to wetlands of uniform vegetation and adequate fetch, however, certain caveats apply. For example, with accurate *R*_{n} and *G* data and small Bowen ratio (β) values, the Bowen ratio energy balance method can give accurate estimates of wetland *ET*. However, large errors in latent heat flux density can occur near sunrise and sunset when the Bowen ratio β≈-1·0. The eddy covariance method provides a direct measurement of latent heat flux density (*E*) and sensible heat flux density (*H*), yet this method requires considerable expertise and expensive instrumentation to implement. A clear advantage of using the eddy covariance method is that E can be compared with *R*_{n}-G-H, thereby allowing for an independent test of accuracy. The surface renewal method is inexpensive to replicate and, therefore, shows particular promise for characterizing variability in *ET* as a result of spatial heterogeneity. LIDAR is another method that has special utility in a heterogeneous wetland environment, because it provides an integrated value for *ET* from a surface. The main drawback of LIDAR is the high cost of equipment and the need for an independent *ET* measure to assess accuracy. If *R*_{n} and *G* are measured accurately, the Priestley-Taylor equation can be used successfully with site-specific calibration factors to estimate wetland *ET*. The 'crop' cover coefficient (*K*_{c}) method can provide accurate wetland *ET* estimates if calibrated for the environmental and climatic characteristics of a particular area. More complicated equations such as the Penman and Penman-Monteith equations also can be used to estimate wetland *ET*, but surface variability and lack of information on aerodynamic and surface resistances make use of such equations somewhat questionable.

I documenti depositati in UnissResearch sono protetti dalle leggi che regolano il diritto d'autore

Repository Staff Only: item control page