Regional evapotranspiration estimates through a triangle method approach
integrating MODIS and MSG-SEVIRI products: application over two
Mediterranean sites
Simona Consoli (1), Mario Minacapilli (2), Daniela Vanella (1), Giuseppe Ciraolo (3),
Antonio Motisi (2)
(1) University of Catania, Dipartimento di Agricoltura, Alimentazione e Ambiente (Di3A),
Italy
(2) University of Palermo, Dipartimento di Scienze Agrarie e Forestali (SAF), Italy
(3) University of Palermo, Department of Civil, Environmental, Aerospace, Materials
Engineering (DICAM), Italy
Evapotranspiration (ET) plays an important role in numerous hydrological processes,
especially those related to water resource management, agriculture, ecology and climate
change. Along with the development of remote sensing technology, the estimation models of
regional ET with remote sensing data have been mainly developed in last three decades, but
there are several related problems that have not yet been solved properly (e.g., need of ground
ancillary data, validation ET data at large scale over heterogeneous surfaces).
In this study, spatially distributed estimates of regional ET were obtained using a new triangle
method approach to parameterize the Priestley-Taylor coefficient (. This method does not
depend on ancillary data, and it is only based on remotely sensed vegetation indexes (EVI)
and diurnal-nighttime land surface temperature differences (LST). Furthermore, in the
proposed approach, the available energy (Rn – G) term of Priestley-Taylor equation is
remotely obtained combining freely available satellite time-series products provided by
MODIS (i.e., EVI, albedo, LSTdiurnal, LSTnight, surface emissivity) and MGS-SEVIRI (i.e.,
short and long wave solar radiation) sensors. The reliability of the triangle method strictly
depends on the identification of the dry and wet edges in the triangular feature space (LSTEVI). In our approach, these boundary conditions (i.e. wet and dry edges) were parameterized
pixel by pixel both in time and space.
Two test different areas (with olive and orange orchards as the main land cover features)
located in the Mediterranean semi-arid conditions of Sicily, were selected for testing and
validating the approach.
Daily ET rates, estimated through the satellite-based proposed method, were validated versus
directly measured fluxes of mass (ET) and net radiation (Rn), obtained by integrating energy
balance methods with Eddy Covariance techniques during the observation period 2010-2012.
The proposed approach allowed predictions of daily evapotranspiration with an acceptable
level of accuracy for practical purposes and therefore it can be considered a simple and
effective tool for an easy estimate of spatial and temporal changes of various hydrological
key-variables related to water resource management, agriculture, ecology and climate change.