Satellite-based modeling of transpiration from the grasslands in the Southern Great Plains, USA

Data from the 2002 International H2O Project (IHOP_2002), which was conducted during May and June 2002 in the Southern Great Plains of the United States, was used to validate a remote sensing-based Vegetation Transpiration Model (VTM). The VTM is based on the linkage between transpiration and photosynthesis, and has been successfully tested over forest landscapes. This study is the first evaluation of the VTM model over grasslands. Since grasslands represent a significant proportion of the Earth's terrestrial surface, this research marks an important step toward applying a satellite-based transpiration model over a landscape that plays a critical role in numerous biogeochemical cycles on both regional and global scales. Comparison of the model output with observer transpiration showed the VTM tended to overestimate transpiration under sparely-vegetated conditions and overestimate transpiration when the vegetation was full. These results indicate that explicitly incorporating the effects of LAI into the VTM could improve model estimates of transpiration; they also underscore the importance of soil evaporation in grassland environments and consequently the need for a companion soil evaporation model that works with the VTM.