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Title: Global Land-surface Evaporation Estimated from Satellite-based Observations

Author
item MIRALLES, DIEGO - Vrije University
item Holmes, Thomas
item DEJEU, RICHARD - Vrije University
item GASH, J - Vrije University
item DOLMAN, A - Vrije University
item MEESTERS, A - Vrije University

Submitted to: Hydrology and Earth System Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2011
Publication Date: 2/3/2011
Citation: Miralles, D.G., Holmes, T.R., DeJeu, R., Gash, J.H., Dolman, A.J., Meesters, A. 2011. Global land-surface evaporation estimated from satellite-based observations. Hydrology and Earth System Sciences. 15:453-459.

Interpretive Summary: Detecting changes in the hydrological cycle is essential if we are to predict the impacts of climate change on agricultural systems. Evaporation is a key component of the global water cycle and there is a need for global evaporation products that can be used to validate components of global circulation models and serve as an observational benchmark for model developers. This paper outlines a new methodology to derive evaporation from satellite observations. The approach uses a variety of satellite-sensor products to estimate daily evaporation at a global scale, with a 0.25 degree spatial resolution. Central to this approach is the use of the Priestley and Taylor (PT) evaporation model. Because the PT equation is driven by net radiation, this strategy avoids the need to specify surface fields of variables, such as the surface conductance, which cannot be detected directly from space. Key distinguishing features are the use of microwave-derived soil moisture, land surface temperature and vegetation density, as well as the use of a detailed rainfall interception module. The modelled evaporation is validated against one year of ground measurements from 44 stations and shows a good performance in all vegetation types and climate conditions.

Technical Abstract: This paper outlines a new methodology to derive evaporation from satellite observations. The approach uses a variety of satellite-sensor products to estimate daily evaporation at a global scale, with a 0.25 degree spatial resolution. Central to this approach is the use of the Priestley and Taylor (PT) evaporation model. Because the PT equation is driven by net radiation, this strategy avoids the need to specify surface fields of variables, such as the surface conductance, which cannot be detected directly from space. Key distinguishing features are the use of microwave-derived soil moisture, land surface temperature and vegetation density, as well as the use of a detailed rainfall interception module. The modelled evaporation is validated against one year of eddy covariance measurements from 44 stations. The estimated annual totals correlate well with the stations’ annual cumulative evaporation (R=0.84, N=44) and show a negligible bias (-1.5%). The validation of the daily time series at each individual station shows good model performance in all vegetation types and climate conditions with an average correlation coefficient of =0.84, still lower than the =0.91 found in the validation of the monthly time series. The first global map of annual evaporation developed through this methodology is also presented.