SATELLITE-BASED EVAPOTRANSPIRATION AND GROSS PRIMARY PRODUCTIVITY FOR THE MID-CONTINENT INTENSIVE CAMPAIGN

Evapotranspiration (ET) and Gross Primary Productivity (GPP) are tightly coupled and play critical roles in regulating the hydrological, climatic, and ecological dynamics at various scales. Accurately estimating ET and GPP over large areas is important but has been challenging due to their variability in space and time. The purpose of this study was to develop a modeling approach for estimating ET and GPP at different spatial and temporal scales. We used temporal Landsat images for the midwestern USA with an energy balance approach for estimating ET and with a light use efficiency method for estimating GPP. The estimated fluxes were compared with measurements from flux towers. We show that energy balance and light use efficiency methods can be effectively used in this region for estimating ET and GPP, respectively. The partitioning of available energy into latent heat (ET) at the surface (evaporative fraction) is constrained by the available moisture and evaporative demand of the atmosphere. The spatial distribution of ET was closely linked to the spatial pattern of GPP on land surfaces. The results also indicate the need for quality assessment of flux tower measurements. The modeling approach used in this study will be implemented using Moderate Resolution Imaging Spectroradiometer (MODIS) images to understand the scaling issues for continental and global study of ET and GPP.