Estimation of vegetation type specific evapotranspiration in a mountainous area using Landsat, field research and SEBS A case study for Vorarlberg, Austria

Abstract

Evapotranspiration is one of the key parameters in the global water balance. It shows a high spatial and temporal variability, especially in mountainous areas. This variability is influenced by climatic and vegetation parameters. Different vegetation species possess different leaf area, root depth and tree height, which all influence evapotranspiration quantities. This research aims to extricate the influence of vegetation characteristics on evapotranspiration from climate spatial variability. Research was carried out in the Austrian province of Vorarlberg which shows a high variation in altitude and subsequent variation in vegetation. Vegetation properties were defined for eight tree species over a small area, in a fieldwork conducted in collaboration with the BioSLIDE project. Remote sensing research was carried out using both Landsat and MODIS images. This remote sensing imagery served as input for modelled evapotranspiration using the SEBS model. From the result a serious unreliability of the MODIS products came to light, related to their low spatial resolution. For this reason, results are based solely on Landsat imagery. Comparison of results shows a considerable difference between evapotranspiration for vegetation species both among individual species and between conifer and deciduous grouped vegetation. Deciduous trees exhibit an average evapotranspiration of up to 1 mm/day above that of coniferous trees. However, this difference can mostly be explained by general position of conifer trees at higher altitude, which in turn relates to lower potential evapotranspiration. For this reason, it can be concluded that climatic spatial variability is the most prominent factor in evapotranspiration modelling.