The WACMOS-ET project – Part 2: Evaluation of global terrestrial evaporation data sets
The WAter Cycle Multi-mission Observation Strategy – EvapoTranspiration (WACMOS-ET) project aims to advance the development of land evaporation estimates on global and regional scales. Its main objective is the derivation, validation, and intercomparison of a group of existing evaporation...
Main Authors: | , , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2016-02-01
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Series: | Hydrology and Earth System Sciences |
Online Access: | http://www.hydrol-earth-syst-sci.net/20/823/2016/hess-20-823-2016.pdf |
Summary: | The WAter Cycle Multi-mission Observation Strategy – EvapoTranspiration
(WACMOS-ET) project aims to advance the development of land evaporation
estimates on global and regional scales. Its main objective is the
derivation, validation, and intercomparison of a group of existing
evaporation retrieval algorithms driven by a common forcing data set. Three
commonly used process-based evaporation methodologies are evaluated: the
Penman–Monteith algorithm behind the official Moderate Resolution Imaging
Spectroradiometer (MODIS) evaporation product (PM-MOD), the Global Land
Evaporation Amsterdam Model (GLEAM), and the Priestley–Taylor Jet
Propulsion Laboratory model (PT-JPL). The resulting global spatiotemporal
variability of evaporation, the closure of regional water budgets, and the
discrete estimation of land evaporation components or sources
(i.e. transpiration, interception loss, and direct soil evaporation) are
investigated using river discharge data, independent global evaporation data
sets and results from previous studies. In a companion article (Part 1),
Michel et al. (2016) inspect the performance of these three models at local
scales using measurements from eddy-covariance towers and include in the
assessment the Surface Energy Balance System (SEBS) model. In agreement with
Part 1, our results indicate that the Priestley and Taylor products (PT-JPL
and GLEAM) perform best overall for most ecosystems and climate regimes.
While all three evaporation products adequately represent the expected
average geographical patterns and seasonality, there is a tendency in PM-MOD
to underestimate the flux in the tropics and subtropics. Overall, results
from GLEAM and PT-JPL appear more realistic when compared to surface water
balances from 837 globally distributed catchments and to separate evaporation
estimates from ERA-Interim and the model tree ensemble (MTE). Nonetheless,
all products show large dissimilarities during conditions of water stress and
drought and deficiencies in the way evaporation is partitioned into its
different components. This observed inter-product variability, even when
common forcing is used, suggests that caution is necessary in applying a
single data set for large-scale studies in isolation. A general finding that
different models perform better under different conditions highlights the
potential for considering biome- or climate-specific composites of models.
Nevertheless, the generation of a multi-product ensemble, with weighting
based on validation analyses and uncertainty assessments, is proposed as the
best way forward in our long-term goal to develop a robust observational
benchmark data set of continental evaporation. |
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ISSN: | 1027-5606 1607-7938 |