HR: 14:15h
AN: A43E-02    [Abstracts]
TI: The effect of vegetation biophysical processes (VBP) on global as well as West African and south American precipitations
AU: * Xue, Y
EM: yxue@geog.ucla.edu
AF: University of California, Los Angeles, 1255 Bunche Hall, Los Angeles, CA 90095, United States
AU: Vasic, R
EM: rvasic@geog.ucla.edu
AF: University of California, Los Angeles, 1255 Bunche Hall, Los Angeles, CA 90095, United States
AU: De Sales, F
EM: fsales@ucla.edu
AF: University of California, Los Angeles, 1255 Bunche Hall, Los Angeles, CA 90095, United States
AU: Mechoso, C R
EM: mechoso@atmos.ucla.edu
AF: University of California, Los Angeles, 1255 Bunche Hall, Los Angeles, CA 90095, United States
AB: Although the role of individual land surface characteristics, such as soil moisture and albedo, in the climate system has been widely recognized, the effects of vegetation biophysical processes (VBP) are not yet fully understood. In this study, VBP effects are assessed using the coupled GCMs and land models under constrain of observed precipitation and reanalysis data. The Simplified Simple Biosphere Model (SSiB) has been coupled to the UCLA atmospheric general circulation model (UCLA AGCM/SSiB-1) to investigate the role and mechanism of land/atmosphere interactions. The coupled system was run for 6-years using climatological sea surface temperature (SST) and the results compared with those obtained with the same AGCM except for the use of an earlier land surface parameterization (UCLA GCM/CNTL). In this earlier version, climatological surface albedo and ground wetness are prescribed and surface temperature is obtained by using a simple single layer energy balance model. The UCLA AGCM/SSiB-1 results indicate a substantial impact from the explicit representation of VBP. The systematic bias in the CNTL precipitation climatology is reduced, especially over land. The annual mean precipitation bias and rms error were reduced by 60% and 40% over global land, respectively. The improvement is consistent for all continents and all seasons. Improvements are most clear in monsoon climate regions, such as West African monsoon and South American monsoon and areas characterized by large landmass, such as the boreal forest areas over the Eurasian and North American continent. These regions also appeared to be the regions sensitive to climate/VBP interactions with the NCEP GCM in other studies. Over West Africa, both bias and rms error in the UCLA GCM/SSiB were reduced by about 80%. Over Amazon, they were reduced by 50% and 25%, respectively. Among four seasons, VBP has significant contribution in spring and summer for most regions over the world, except West Africa, where VBP has significant effect over all four seasons. These results indicate that under unstable atmospheric conditions, not only low frequency mean forcings from the land surface, such as monthly mean albedo, but also VBP perturbation processes are important to the continental scale precipitation. A realistic representation of VBP in the GCM, therefore, is important for global water and energy studies. It is particular crucial to the monsoon climate regions such as West Africa and South America and areas characterized by large landmass such as the boreal forest zone.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0429 Climate dynamics (1620)
DE: 0495 Water/energy interactions (1878)
DE: 0545 Modeling (4255)
DE: 1833 Hydroclimatology
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly