Assessment of actual evapotranspiration over a semiarid heterogeneous land surface by means of coupled low-resolution remote sensing data with an energy balance model: comparison to extra-large aperture scintillometer measurements
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Published:2018-04-09
Issue:4
Volume:22
Page:2187-2209
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ISSN:1607-7938
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Container-title:Hydrology and Earth System Sciences
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language:en
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Short-container-title:Hydrol. Earth Syst. Sci.
Author:
Saadi Sameh, Boulet GillesORCID, Bahir MalikORCID, Brut Aurore, Delogu Émilie, Fanise Pascal, Mougenot Bernard, Simonneaux Vincent, Lili Chabaane ZohraORCID
Abstract
Abstract. In semiarid areas, agricultural production is restricted by water
availability; hence, efficient agricultural water management is a major issue.
The design of tools providing regional estimates of evapotranspiration (ET),
one of the most relevant water balance fluxes, may help the sustainable
management of water resources. Remote sensing provides periodic data about actual vegetation temporal
dynamics (through the normalized difference vegetation index, NDVI) and water
availability under water stress (through the surface
temperature Tsurf),
which are crucial factors controlling ET. In this study, spatially distributed estimates of ET (or its energy
equivalent, the latent heat flux LE) in the Kairouan plain (central Tunisia)
were computed by applying the Soil Plant Atmosphere and Remote Sensing
Evapotranspiration (SPARSE) model fed by low-resolution remote sensing data
(Terra and Aqua MODIS). The work's goal was to assess the operational use of
the SPARSE model and the accuracy of the modeled (i) sensible heat flux (H)
and (ii) daily ET over a heterogeneous semiarid landscape with complex
land cover (i.e., trees, winter cereals, summer vegetables). SPARSE was run to compute instantaneous estimates of H and LE fluxes at the
satellite overpass times. The good correspondence (R2 = 0.60 and 0.63
and RMSE = 57.89 and 53.85 W m−2 for Terra and Aqua,
respectively) between instantaneous H estimates and large aperture
scintillometer (XLAS) H measurements along a path length of 4 km over the
study area showed that the SPARSE model presents satisfactory accuracy.
Results showed that, despite the fairly large scatter, the instantaneous LE
can be suitably estimated at large scales (RMSE = 47.20 and 43.20 W m−2
for Terra and Aqua, respectively, and R2 = 0.55 for both
satellites). Additionally, water stress was investigated by comparing
modeled (SPARSE) and observed (XLAS) water stress values; we found that most
points were located within a 0.2 confidence interval, thus the general
tendencies are well reproduced. Even though extrapolation of instantaneous
latent heat flux values to daily totals was less obvious, daily ET estimates
are deemed acceptable.
Publisher
Copernicus GmbH
Subject
General Earth and Planetary Sciences,General Engineering,General Environmental Science
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