1. Deforestation and the Stream Flow of the Amazon River -- Land Surface Processes and Atmospheric Feedbacks
Michael T. Coe1, Marcos Heil Costa2, and Britaldo Soares-Filho3
1The Woods Hole Research Center, Woods Hole, MA
2Universidade Federal de Viçosa
3Universidade Federal de Minas Gerais
Talk about our recent use of numerical models to understandthe historical and future influence of deforestation on streamflow in the basin

2. Land Cover Change Potential
Original vegetation dominated by evergreen forest and Cerrado biomes.
Only large scale example available is one by Marcos Costa et al.,
Compared observed discharge of Tocantins for 2 periods
early period where cropland covered roughly 30% of basin
later period where cropland increased to about 50% of basin
Ramankutty and Foley, 1998

3. Land Cover Change
About 15% of basin is currently deforested, 50% of Cerrado, 10% of evergreen forest
Demand for agricultural and forest products is currently high
Possibility exists for large increase in the deforested area.
2000
Eva et al., 2000
Figure: Paul Lefebvre

4. Land Cover Change
Soares-Filho et al., 2006 developed scenarios of future deforestation
Prescribed governance rules limiting deforestation in individual locations
GOV-2050
Only large scale example available is one by Marcos Costa et al.,
Compared observed discharge of Tocantins for 2 periods
early period where cropland covered roughly 30% of basin
later period where cropland increased to about 50% of basin
About 35% of basin deforested by 2050
Soares-Filho et al., 2006

5. Land Cover Change
Soares-Filho et al., 2005 developed scenarios of future deforestation
Business-as-Usual where current trends are extrapolated to future with no control on total deforestation
BAU-2050
Some change will occur and will affect terrestrial and riverine ecosystems
About 50% of basin deforested by 2050
Soares-Filho et al., 2006

6. Land cover changes affect the energy and water balance -- at two scales
Locally – small and large scale observations show that deforestation causes:
Decreased evapotranspiration
Decreased rooting depth
Decreased LAI
Less soil infiltration
Increased runoff and river discharge
We have seen this in SE Amazonia already…

7. Land Cover Change and Tocantins -- Costa et al., 2003
2000
km2
Compared two periods ;
Pasture and cropland increased from 30% of basin in 1960 to 50% of basin by 1995
Only large scale example available is one by Marcos Costa et al.,
Compared observed discharge of Tocantins for 2 periods
early period where cropland covered roughly 30% of basin
later period where cropland increased to about 50% of basin
Costa et al., 2003

8. Discharge of Tocantins Before and After Change
After land cover change
1950s-60s
1980s-90s
Discharge
Before change
Coincident with those changes in land use…
Found a 25% increase in the annual discharge with no significant change in precipitation. 30% in the wet season, plus one month earlier.
Therefore, recent land cover change had big impact on water budget of this river. As the rains that fall are not used by the crops as much as by the previous natural vegetation, runs off landscape and discharge increases.
Observed 25% increase in annual discharge with no change in rainfall
Maximum discharge is one month earlier
Costa et al., 2003

9. Land Cover Change and Araguaia -- Coe et al., 2008
82000 km2 basin upstream of Aruanã
Compared two periods ;
Pasture and cropland increased from 25% of basin in 1975 to about 60% of basin by 1995
Only large scale example available is one by Marcos Costa et al.,
Compared observed discharge of Tocantins for 2 periods
early period where cropland covered roughly 30% of basin
later period where cropland increased to about 50% of basin
Coe et al., 2008

10. Discharge of Araguaia Before and After Change
After land cover change
Before change
Z-test for comparison of mean monthly discharge of two periods – highly significant difference (0.0002)
Hydrology of SE Amazon appears to be responding to deforestation
Observed 25% increase in discharge
2% increase in rainfall
Requires 4% decrease in ET
Coe et al., 2008

11. Land cover changes affect the energy and water balance -- at two scales
Regionally – Global and regional climate models suggest that when large enough (~> s km2):
Decreased evapotranspiration, increased sensible heat flux
Decreased net energy
Increased albedo
Human changes to land cover will impact hydrology…
Many small-scale studies have shown that in general, evaporation decreases and runoff and river discharge increase with increasing deforestation.
Chemical composition of runoff and discharge also changes as soil materials become mobilized and management practices change.
And additionally… as Roni Avissar showed Large-scale land cover changes may lead to large changes in rainfall pattern and amount

12. Albedo difference is large.
Upper Xingu

13. Without strong evaporation, transfer of energy to atmosphere occurs via much greater sensible heat flux.
Upper Xingu

14. Land cover changes affect the energy and water balance -- at two scales
Regionally – Global and regional climate models suggest that when large enough (~> s km2):
Decreased moisture convergence
Decreased rainfall
Decreased runoff and discharge
Human changes to land cover will impact hydrology…
Many small-scale studies have shown that in general, evaporation decreases and runoff and river discharge increase with increasing deforestation.
Chemical composition of runoff and discharge also changes as soil materials become mobilized and management practices change.
And additionally… as Roni Avissar showed Large-scale land cover changes may lead to large changes in rainfall pattern and amount

15. Combined effect of local and regional influences will be complex
Increased runoff from local ET decrease
Decreased runoff from climate feedbacks and decreased regional precipitation

16. Combined effect of local and regional influences will be complex
Exact response will depend on:
How much of individual watershed has been deforested.
How much of the entire Amazon has been deforested.

17. Hypotheses
2000
GOV-2050
BAU-2050
Land cover change within the Amazon has already resulted in large changes in discharge due to local ET decrease.
Influences will increase and become more complex as deforestation expands.
Influences will increase as we move to a progressively deforested Amazon

18. Modeling Land Surface Processes and Atmospheric Feedbacks
Perform suite of simulations with land surface and climate models to answer:
Has land cover change affected streams already?
Are future atmospheric feedbacks of potentially important scale?
Are there important differences in future scenarios for the Amazon River?
1. Observations say yes, do the simulations back it up?
2. Do we have to worry about them also?
3. In other words, do conservation strategies have strong outcome?

19. Modeling Land Surface Processes and Atmospheric Feedbacks -- Models
IBIS land surface model
Partitions incoming radiation and precipitation into surface and sub-surface energy and water balance
CCM3-IBIS coupled climate and land surface model
Simulate dynamic equilibrium between climate and vegetation, feedbacks between land surface changes and the atmosphere
THMB water transport model
Simulate river discharge and flood plain inundation
Models we have developed and applied over course of LBA – not going to go into details of the models here

20. Modeling Land Surface Processes and Atmospheric Feedbacks -- Methods
IBIS/THMB alone
Prescribed historical climate
4 prescribed vegetation scenarios
Potential -- Control
Modern
2050 Governance
2050 Business-as-usual
influence of deforestation on local ET only – no climate feedback

21. Modeling Land Surface Processes and Atmospheric Feedbacks -- Methods
CCM3-IBIS/THMB coupled
Simulate dynamic equilibrium between climate and vegetation
3 prescribed vegetation scenarios
Potential -- Control
2050 Governance
2050 Business-as-usual
Combined influence deforestation on local ET and regional precipitation

22. IBIS/THMB alone – modern deforestation and local ET
CTL Predominantly tropical evergreen forest and Cerrado
MOD pasture and agriculture have replace 15% of native vegetation
2 simulations with prescribed historical climate and different land cover
Any difference in simulations is function of land cover change alone

23. MOD - CTL Discharge increase proportional to land cover change
See large simulated increase in Tocantins and modest increases in other basins of the SE Amazon – proportional to amount of basin deforested.
Shown as fractional difference from CTL (potential vegetation) simulation
Discharge increase proportional to land cover change

24. Tocantins River – 1990s Observed -- black
Mean monthly discharge in in the 1990s
Observed -- black
Simulated No deforestation -- green

25. Tocantins River – 1990s Observed -- black
Achieve agreement with observations only if observed deforestation is included
NOTE: With potential vegetation simulations agree in 1950s but diverge from observations with time
Agreement returns in 1990s in MOD simulation
2/3 of change between periods is a function of land cover change
Observed -- black
Simulated No deforestation – green
Simulated with modern vegetation -- red

26. Original Questions Has land cover change affected streams already?
In SE Amazonia discharge agrees with observations in the 1990s only if land cover change is included
Strongly suggests that observed change in discharge over last few decades is largely a result of deforestation
In fact. 2/3 is due to deforestation, 1/3 precipitation increase

27. IBIS/THMB alone – future deforestation and local ET
So what might happen in the future?
~35% deforested
~50% deforested
2 simulations with prescribed historical climate and different land cover
Any difference in simulations from CTL is a function of land cover change alone

28. IBIS/THMB alone – future deforestation and local ET
BAU
GOV
GOV and BAU, increased in all watersheds, strong differences in those basins in SE where Governance reduces deforestation. Note that Tocantins has little difference because is largely deforested in GOV
Discharge is increased in all watersheds proportional to the area deforested

29. IBIS/THMB alone – future deforestation and local ET
MOD
BAU
GOV
Compared to what has already occurred. - - In absence of atmospheric feedback expect large change in watersheds in SE Amazonia
So how important might climate feedbacks be?
In absence of atmospheric feedback predicted change is large in SE Amazonia

30. CCM3/IBIS/THMB coupled
… question is How important will climate feedbacks be?
~35% deforested
~50% deforested
Simulations with prescribed land cover and dynamic climate
Any difference in simulations from CTL is function of land cover change and climate feedback

31. CCM3/IBIS/THMB coupled
GOV
BAU
Precipitation decrease in ALL basins (5-20%)
Discharge decrease in most basins
Significant difference between GOV and BAU

32. CCM3/IBIS/THMB coupled
Tocantins and Madeira have largest deforestation –local ET decrease is larger than precipitation decrease
Tapajos and Xingu similar precipitation decrease but different response because much less high deforestation in Xingu
Madeira and Tocantins have largest deforestation (GOV = 41%, 80%)
Net positive change - local ET decrease is larger

33. CCM3/IBIS/THMB coupled
Tocantins and Madeira have largest deforestation –local ET decrease is larger than precipitation decrease
Tapajos and Xingu similar precipitation decrease but different response because much less high deforestation in Xingu
Tocantins and Xingu have similar precipitation decrease (GOV = -15%)
Xingu is less deforested (25% vs 80%)

34. Synthesis Streams are currently dominated by local effects
Streams will follow current trajectory in the near-term
Should see large shift in future when deforestation in entire basin reaches some threshold (~40%?)
GOV
BAU

35. Original Questions
Are the changes to the future energy and water balance of potentially important scale?
Effect of climate feedback is of same scale and opposite sign as local ET decrease from deforestation
Changes not limited to those basins where deforestation takes place
Indicates that climate feedbacks are likely to be important factor in future of river

36. Original Questions
Are there important differences in future scenarios for the Amazon River?
Governance of deforestation reduces change relative to business as usual
Policies favoring forest conservation will potentially have a large influence on the river

37. Summary
Deforestation and Local ET changes appear to have already increased discharge in SE Amazonia
Future changes due to regional climate feedbacks are likely to be as large and opposite in sign to the local changes
The Integrated effect in any watershed will be some complex function of local and Amazon-wide deforestation
Future studies will need to investigate impact on extreme events because this is where greatest ecosystem disruption will occur.
Can and HAS been used to understand…
On our way to providing a tool that can be of use to many different groups.

39. CCM3/IBIS/THMB coupled BAU 2050
Xingu
66% deforested
20% precipitation decrease
17% discharge decrease

40. CCM3/IBIS/THMB coupled BAU 2050
Xingu
66% deforested
20% precipitation decrease
17% discharge decrease
Tocantins/Araguaia
93% deforested
14% precipitation decrease
8% discharge increase

41. IBIS/THMB alone – the effect of modern deforestation