An Assessment of the Surface Energy and Water Balance in Mediterranean Desert Areas based only on Satellite Data

Among the studies on the interactions between the land surface and the atmosphere, the estimation of the surface energy budget in desert areas is of great interest in different applications, like the influence on the climate and the study of the desertification dynamics. Given the scarcity or the complete lack of ground sensors, the large scale assessment of the state of the desert regions and of the surrounding vegetation requires the use of remote sensing techniques on satellite platforms. The main prognostic variable that retains information about the energy budget at the interface between land and atmosphere is the Land Surface Temperature (LST). In this work the LST assimilation model ACHAB, designed for the estimation of the fluxes of sensible and latent heat (evapotranspiration), was employed to assess the energy and water budget through the use of sequences of LST maps from satellite platforms. The LST data were taken from measurements of the MODIS sensor aboard Terra and Aqua satellites, while the auxiliary data at the ground (air temperature, solar radiation, etc.) were estimated basing on a disaggregation of the large scale NCEP reanalysis fields. The domain of the study consisted in the desert areas of the Mediterranean, namely some of the southern regions of Europe and the Mediterranean Africa, while the period considered was 2003- 2006. The results in terms of maps of evapotranspiration and evaporative fraction were compared with maps of FAPAR (Fraction of Absorbed Photosynthetically Active Radiation) obtained by SeaWiFS platform, showing good agreement in terms of trends and spatial patterns. A discussion of the results, also in terms of maps and trends of desertification, is presented.