92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Sunday, 22 January 2012
Deciduous-Broadleaf Forest Simulation Accuracy in the Community Land Model v4.0
Hall E (New Orleans Convention Center )
Walter Andre Perkins, UCAR, Boulder, CO; and G. Bonan

Seasonal changes in leaf area index (LAI) are an important factor in determining radiative transfers, and ecosystem exchanges between the land and atmosphere components of the Community Land Model (CLM). Thus, striving for more accurate vegetation simulations will yield more realistic results from the CLM. A recent study showed a possible problem with the spring green-up in the vegetation simulation of a deciduous-broadleaf forest. This study was conducted using an older version of the CLM with an early prototype of the carbon-nitrogen (CN) biogeochemical model. The result of that study prompted an investigation into the current behavior of deciduous-broadleaf forests in the CLM v4.0. To investigate current behavior, we employed a multi-grid-cell, multi-year, monthly average of a prognostic and prescribed vegetation simulations, and also used averages of observed data from AmeriFlux tower sites. LAI values between the two simulations and observations were compared, and then effects on latent heat flux (LH), sensible heat flux (SH), gross primary production (GPP), and the net ecosystem exchange (NEE) were assessed. Comparisons show that although there has been an improvement in the seasonal behavior of LAI, the LAI for the simulated vegetation is biased high. The high LAI causes increases of GPP and LH, and a decrease in SH. The NEE is underestimated during summer and overestimated during winter, but this does not appear to be caused by the high LAI values. These biases highlight the need for further study and improvement of CN model, and CLM accuracy.

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