Evaluation of Evapotranspiration Component in Global Climate Model

Evapotranspiration (ET) is a major component of regional and global hydrologic cycle. However, in most cases ET is not included in model evaluation or validation, because of the lack of long term observation data. Global network of over 400 flux measurement sites (FLUXNET) provide continuous measurements of carbon, water and energy fluxes over the last decade. The broader goal of this research is to use these flux data in conjunction with reanalysis data to improve regional scale hydrologic predictions by global climate model. In this study, energy flux data from 72 AmeriFlux sites ranging from one year to 15 years length, and spread over 10 land cover types are analyzed. Climatology of AmeriFlux measurements for different land cover types are compared with high resolution North American Regional Reanalysis (NARR) data and Community Climate System Model (CCSM Version 3.0.1) output. In agriculturally dominated Midwest region, NARR climatology of latent and sensible heat flux agrees well with the AmeriFlux measurements at 4 crop sites, whereas coupled simulation of CCSM highly overestimates sensible heat flux and underestimates latent heat flux during the summer months. Results from off line simulation of CLM3.5 (land component of CCSM) will also be presented.