Assessment of the Basin-Scale Land Surface Energy Budget in the NCEP Operational and Research NLDAS-2 Systems

This paper compares the annual and monthly components of the simulated energy budget from the North American Land Data Assimilation System phase 2 (NLDAS-2) with observations over the domains of the twelve River Forecast Centers (RFCs) of the continental U.S. (CONUS). The simulations are calculated from both operational and research versions of NLDAS-2. The observed radiation components are obtained from the National Aeronautics and Space Administration (NASA) Surface Radiation Budget (SRB) product. Sensible and latent heat fluxes are obtained from a multi-tree-ensemble (MTE) method applied to gridded FLUXNET data from the Max-Planck Institute, Germany. As these observations are obtained from different data sources, they cannot fully close the energy budget. The range of closure error is less than 15% for mean annual results, although this closure error is substantial. The analysis here demonstrates the usefulness of basin-scale surface energy budget analysis for evaluating model skill and deficiencies. The operational (i.e., Noah, Mosaic, VIC) and research (i.e., Noah-I and VIC4.0.5) NLDAS-2 land surface models (LSMs) exhibit similarities and differences in depicting basin-averaged energy components. For example, the energy components of the five LSMs have similar seasonal cycles, but with different magnitudes. Generally, Noah and VIC overestimate (underestimate) sensible (latent) heat flux over several RFCs of the eastern CONUS. In contrast, Mosaic underestimates (overestimates) sensible (latent) heat flux over almost all twelve RFCs. The research Noah-I and VIC4.0.5 versions show moderate-to-large improvements (albeit basin and model dependent) relative to their operational versions, which indicates likely pathways for future improvements in the operational NLDAS-2 system.