The effect of vegetation biophysical processes VBP on the global precipitation

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The effect of vegetation biophysical processes
(VBP) on the global precipitation Yongkang
Xue1,2, Fernando De Sales1, Ratko Vasic1, C.
Roberto Mechoso2 1. Department of Geography,
UCLA. 2. Department of Atmospheric Oceanic
Sciences, UCLA
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Scientific Goals 1). The temporal and spatial
characte-ristics of effects of vegetation
biophysical processes (VBP) on the precipitation
at global and continental scales. 2). Identify
the major regions and processes, which VBP affect
the most. 3). Assess the results uncertainty
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1st exp UCLA GCM with two surface processes
schemes

• Original UCLA GCM Specified monthly mean soil
  moisture with monthly mean vegetation albedo
• SSiB radiative transfer at canopy,
  transpiration, interception loss,
  vegetation-modified surface resistance,
  vegetation and soil property based on vegetation
  types, etc.
• Six year simulations with climatological SST.
  Five year means are presented.

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Annual cycle of observed and simulated monthly
mean precipitation mm/day
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5-day precipitation evolution over western
Africa Longitude (-15 20)
mm/day
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Simulation Biases and RMS errors
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Simulation Bias and RMS errors
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Simulation Bias and RMS errors
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2nd experiment

• Case S Explicit vegetation NCEP GCM/SSiB
• Case C No explicit vegetation NCEP GCM/soil
  model
• Integration May 1987 to April 1988
• Two land surface models use the same initial soil
  moisture and have similar monthly mean surface
  albedo

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• Summary
• 1). Effects of vegetation biophysical processes
  (VBP) are assessed using the coupled GCMs and
  land models under constrain of observed
  precipitation and reanalysis data.
• 2). Over land, the effects mainly appeared over
  the monsoon regions, boreal forest regions,
  central and eastern U.S., and west Europe with
  spring and summer seasons having the most
  dramatic impact. West Africa has strong impacts
  during all four seasons.

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• 3). Over the ocean, most effects appear in
  Atlantic ITCZ and SACZ, The Gulf of Mexico, Bay
  of Bengal, West Pacific.
• 4). It shows that in general more realistic VBP
  specification produced better precipitation
  simulations. VBP processes in GCMs are crucial
  for adequate simulations of water and energy
  cycles over land.

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• 5). Two GCMs with different numerical schemes and
  different simple land schemes show consistent
  response to the VBP forcing but with some
  regional discrepancy.
• 6). Land surface processes include soil moisture
  process, VBP, snow process, etc. It is important
  to include all these components in land/
  atmosphere interaction studies.