Evapotranspiration Estimates from Remote Sensing for Irrigation Water Management - Satellite-based Applications on Climate Change - page 206

Application of METRIC for ET mapping at Landsat scale can be used to assess
the impacts of climate change on future water consumption. Rates and spatial
variation of ET are derived over large areas and at relatively fine resolution,
providing substantial input to other hourly or daily land surface process models
that can, in turn, be applied with climate projections. Because METRIC requires no
a priori knowledge of soil water content, the ET estimates from METRIC are
independent of biases or assumptions regarding vegetation physiology and phenol-
ogy. This allows derivation of vegetation-related parameters by inverting
components of the energy balance produced by METRIC with less bias and
independent of the process models.
A METRIC-produced image from Landsat or MODIS satellites can be sampled
using basic GIS analysis to provide numerous combinations of ET, vegetation
amount, relative water availability, and ambient air and surface temperature.
Analysis of these combinations can increase understanding of how various vegeta-
tion communities may behave under different levels of water, environmental, and
management stressors. METRIC and other satellite-based analyses also provide the
means to extend local studies and measurements of surface energy and CO 2 fluxes
to much larger areas by confirming or bias-correcting model calibration and for
particular vegetation types.
Acknowledgements Some contents in Sect. 4 describing the METRIC model are derived from
Allen et al. ( 2011 ).
This work was funded by the World Bank under the guidance of Mr. Hassan Lamrani, the
World Bank, Rabat. The authors recognize and thank the Tadla, Doukkala, and Haouz ORMVAs
for providing data and insight into irrigation systems management and operations.
In addition to the authors, this study was conducted by a team of scientists and engineers from
Morocco and USA (in alphabetical order): Graeme Aggett, Nils Babel, Omar Berkat, Mohammed
Bourass, Jan Hendrickx, Said Ouattar, Claudio Schneider, and Ricardo Trezza. The views,
opinions, and findings contained in this publication are those of the authors and should not be
considered official position, policy, or decision.
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