Remotely-sensed evapotranspiration of typical oasis in the southern edge of tarim basin and its relationship to land cover changes

Abstract

The oasis vegetation evapotranspiration (ET) is a sensitive factor for the arid land surface water-heat exchange caused by land cover changes, which is very important on the feedback between terrestrial ecosystems and climate change. Evapotranspiration in Keriya Oasis of the Tarim Basin was calculated and spatially exhibited in this study by integrating remote sensing data into the Surface Energy Balance Algorithm for Land (SEBAL) model, which was modified and improved by COST atmospheric correction model and mono-window land surface temperature (LST) retrieval algorithm. The Landsat ETM+ imagery, in combination of the meteorological data collected in ground stations, was employed in SEBAL model for estimating oasis surface parameters and vegetation structure parameters in Keriya Oasis. Based on the instantaneous ET estimated by SEBAL, the average and maximum daily ET was calculated to map the spatial differentiation of oasis vegetation ET. Thereafter, the relationship between spatial difference of actual ET and land cover types was analyzed in detail. With the decreasing of mean surface ET, the land use type transferred from wetland, water body, cropland, high densely populated grassland to low densely populated grassland (ecotone) and desert. The actual ET had a certain correlation relationship with NDVI which indicated the features of land cover, thus different land cover type and surface water condition in Keriya Oasis were characterized and distinguished by the Temperature Vegetation Dryness Index (TVDI) and obviously exhibited in NDVI-LST feature space. Land cover type and vegetation density, as well as soil moisture distribution, were identified as the most important biophysical and hydrological parameters influencing the spatial and temporal variation of oasis vegetation ET.