Modelling surface energy fluxes over a dehesa ecosystem using a two-source energy balance model and medium resolution satellite data

The dehesa, the most widespread agroforest ecosystem in Europe(approximate to 3 million ha), is recognized as an example of
sustainable land use and for its importance in rural economy (\{[\}1]
\{[\}2]). It is characterized by widely-spaced oak trees (mostly Quercus
Ilex L.), combined with crops, pasture and shrubs in the sub-canopy
region. The estimation of the ecosystem evapotranspiration (ET) using
remote sensing may assist the monitoring of its state from local to
regional scales, improving the management and the conservation of the
ecosystem. Thermal-based energy balance techniques which distinguish
soil/substrate and vegetation contributions to the radiative temperature
and radiation/turbulent fluxes have proven to be reliable in the
estimation of the energy surface fluxes, and therefore in the estimation
of ET. In particular, the two-source energy balance (TSEB) model of
Norman et al. (\{[\}3]) and Kustas and Norman (\{[\}4]) has shown to be
robust for semi-arid sparse canopy-cover landscapes. With the objective
of evaluating the model over this environment, an energy flux
measurement system has been used. It was installed in a dehesa located
in Southern Spain (38 degrees 12' N; 4 degrees 17' W, 736 m a.s.l) with
1 km homogeneous fetch in wind direction. The quality of the measured
data fluxes has been tested with the energy-balance closure criterion
(\{[\}5] \{[\}6]) yielding an average closure of 86% which is within the
error range found in similar studies. The TSEB model was evaluated in
the area for 2012 summer season, using images from MODIS (Moderate
Resolution Imaging Spectroradiometer) sensor and ground measured
meteorological data. The half-hourly estimates were compared with the
flux tower measurements, obtaining a RMSD between modeled and measured
energy fluxes within the closure balance error.