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Supporting Information
Model description
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~3°), and relative to the observations, the simulated climatological distribution of
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precipitation over tropical South America is reasonably good in this model version
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outside the vicinity of the Andes, although details of precipitation feature need to be
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improved (Figure S1). Annual mean present-day minus pre-land use vegetation
We performed simulations with the NCAR CAM3-CLM3.5 at T42 resolution (~3° by
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differences in leaf area index (LAI) are plotted in Figure 2b. Since the exchange of water
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(and carbon) between the biosphere and the atmosphere occurs within leaves of plants,
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LAI is the main variable that controls transpirational flux. The difference map in Fig 2b
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illustrates a large negative difference of present-day minus pre-land use vegetation LAI
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over southern tropical South America, which we view here as a proxy for the
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deforestation/land use change signature (for more information on the pre-land use
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vegetation mapping, see Lawrence and Chase, 2010).
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Table S1. Simulated precipitation and temperature differences due to SST, vegetation,
and both SST and vegetation over northern (latitude: 5S-5N, longitude 70W-60W)
and southern (latitude: 10S-0, longitude 60W-50W) tropical South America (blue and
brown boxes in Figure 1, respectively). The effect of SST only is the ensemble mean
differences from the control run differences from 1993-2006 to 1979-1992, and the effect
of vegetation only is the ensemble mean differences from the present-day vegetation to
pre-landuse vegetation cases for the whole period (1979-2006). The combined effect of
SST and vegetation is the ensemble mean difference from 1993-2006 with present-day
vegetation to 1979-1992 pre-landuse vegetation cases. Observation is GPCP
precipitation (43) difference and GHCN temperature (44) difference between the average
of 1993-2006 and of 1979-1992. Northern part temperature is not available from GHCN
data because of the lack of the observation. Values in parentheses represent standard
deviation.
Model
Observation
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SST
Vegetation
Total
P (mm/year)
Northern
Southern
+108 (160)
-12 (124)
+13 (150)
-70 (131)
+125 (160)
-82 (132)
+127 (148)
-70 (146)
T (C)
Southern
+0.2 (0.34)
+0.5 (0.40)
+0.7 (0.35)
+0.5 (0.22)
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44
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Table S2. Simulated water budget (mm/year) over northern (latitude: 5S-5N, longitude
70W-60W) and southern (latitude: 10S-0, longitude 60W-50W) tropical South
America (blue and brown boxes in Figure 1, respectively). SST only forcing shows the
differences in responses due to SST between the average of 1993-2006 and of 1979-1992,
and vegetation forcing shows the differences between potential and present-day
vegetation. The increase in precipitation in northern SA is the result of increased wind
convergence whereas the decrease in southern SA is largely due to the decrease in
evapotranspiration associated with lower vegetation coverage. V is horizontal wind
vector, q is specific humidity, E is evaporation, and P is precipitation. All divergence
terms are vertically integrated.
V  q
V  q


E
P
48
49
Differences due to SST only
Northern SA
Southern SA
-1
8
-6
14
1
13
119
-48
17
-5
127
-13
Differences due to vegetation only
Northern SA
Southern SA
4
-29
-15
-12
-0.4
-4
19
32
10
-47
17
-70
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Figure S1. Mean annual precipitation (mm/year) from the GPCP merged data (top) and
CAM3 model simulation (bottom). Simulated precipitation is reasonably good outside
the vicinity of the Andes.
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Figure S2. Mean monthly Bowen ratio for the southern part (brown box in Figure 1).
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Figure S3. Gross primary productivity for the pre-landuse (blue) and present-day (red)
vegetation runs over the southern part (brown box in Figure 1).