Validation of the NOAH-OSU land surface model using surface flux measurements in Oklahoma

Oklahoma Atmospheric Surface-Layer Instrumentation System (OASIS) measurements of net radiation (R-n), latent heat flux (LH), sensible heat flux (SH), and ground heat flux (GH) were used to validate the NOAH-Oregon State University Land Surface Model (NOAH-OSU LSM). A 1-year study period was used. R-n, LH, SH and GH data from seven sites were screened based on an energy balance closure criterion (daily/hourly sum of the flux components within the range of -10 to +10 W m(-2)). The vegetation fraction used in the model was computed using both the Gutman-Ignatov (G-I) and the Carlson-Ripley (C-R) schemes. The simulated net radiation and ground heat fluxes seem less sensitive to the choice of schemes for computing green vegetation fraction, while latent and sensible heat flux show more sensitivity particularly for soil dry-down period. Therefore, the G-I approach was used for the validation study, as it is widely used and linear in its form. The daily aggregated model outputs showed that the predicted R-n had a positive bias of 0.8 MJ m(-2) d(-1) and an RMSE of 1.6 MJ m(-2) d(-1) when averaged over all seven sites. The seven-site average bias in LH was about 0.9 MJ m(-2) d(-1) with an RMSE of 2.5 MJ m(-2) d(-1). The bias in SH and GH was low and positive with an RMSE of about 2.2 MJ m(-2) d(-1) in SH estimation. The hourly average output showed similar results, with the exception that GH had a negative bias. The overall performance of the NOAH-OSU LSM was good for a diverse set of Oklahoma conditions.