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, MA2Universidade Federal de Viçosa

3Universidade Federal de Minas Gerais

Land Cover Change

• Original vegetation dominated by evergreen forest and Cerrado biomes.

Ramankutty and Foley, 1998

Potential

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.

Eva et al., 2000

Figure: Paul Lefebvre

2000

Land Cover Change

• Soares-Filho et al., 2006 developed scenarios of future deforestation

• Prescribed governance rules limiting deforestation in individual locations

Soares-Filho et al., 2006About 35% of basin deforested by 2050

GOV-2050

Land Cover Change

Soares-Filho et al., 2006

• 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

About 50% of basin deforested by 2050

BAU-2050

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

Land cover changes affect the energy and water balance -- at two scales

Land Cover Change and Tocantins -- Costa et al., 2003

• 175000 km2 • Compared two periods

1949-1968; 1979-1998• Pasture and cropland

increased from 30% of basin in 1960 to 50% of basin by 1995

Costa et al., 2003

2000

Discharge of Tocantins Before and After Change

• Observed 25% increase in annual discharge with no change in rainfall

• Maximum discharge is one month earlier Costa et al., 2003

Figure 6

1950s-60s 1980s-90s

After land cover change

Before changeD

isch

arge

Land Cover Change and Araguaia -- Coe et al., 2008

• 82000 km2 basin upstream of Aruanã

• Compared two periods 1970-1979; 1990-1999

• Pasture and cropland increased from 25% of basin in 1975 to about 60% of basin by 1995

Coe et al., 2008

Discharge of Araguaia Before and After Change

• Observed 25% increase in discharge• 2% increase in rainfall• Requires 4% decrease in ET

Coe et al., 2008

After land cover change

Before change

Regionally – Global and regional climate models suggest that when large enough (~> 100000s km2):

• Decreased evapotranspiration, increased sensible heat flux

• Decreased net energy– Increased albedo

Land cover changes affect the energy and water balance -- at two scales

Upper Xingu

Upper Xingu

Regionally – Global and regional climate models suggest that when large enough (~> 100000s km2):

• Decreased moisture convergence• Decreased rainfall• Decreased runoff and discharge

Land cover changes affect the energy and water balance -- at two scales

• Increased runoff from local ET decrease• Decreased runoff from climate

feedbacks and decreased regional precipitation

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.

Combined effect of local and regional influences will be complex

• 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.

Hypotheses

2000 GOV-2050 BAU-2050

Perform suite of simulations with land surface and climate models to answer:

1. Has land cover change affected streams already?

2. Are future atmospheric feedbacks of potentially important scale?

3. Are there important differences in future scenarios for the Amazon River?

Modeling Land Surface Processes and Atmospheric Feedbacks

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

Modeling Land Surface Processes and Atmospheric Feedbacks -- Methods

• IBIS/THMB alone- Prescribed historical climate 1939-2000- 4 prescribed vegetation scenarios

-Potential -- Control-Modern-2050 Governance -2050 Business-as-usual

- influence of deforestation on local ET only – no climate feedback

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

IBIS/THMB alone – modern deforestation and local ET

• 2 simulations with prescribed historical climate 1939-2000 and different land cover• Any difference in simulations is function of land cover change alone

Discharge increase proportional to land cover change

MOD - CTL

Observed -- black

Simulated No deforestation -- green

Tocantins River – 1990s

Observed -- black

Simulated No deforestation – green

Simulated with modern vegetation -- red

Tocantins River – 1990s

1. 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

Original Questions

IBIS/THMB alone – future deforestation and local ET

~35% deforested ~50% deforested

• 2 simulations with prescribed historical climate 1939-2000 and different land cover• Any difference in simulations from CTL is a function of land cover change alone

Discharge is increased in all watersheds proportional to the area deforested

IBIS/THMB alone – future deforestation and local ET

GOV

BAU

In absence of atmospheric feedback predicted change is large in SE Amazonia

IBIS/THMB alone – future deforestation and local ET

GOV

BAU

MOD

CCM3/IBIS/THMB coupled

~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

• Precipitation decrease in ALL basins (5-20%)• Discharge decrease in most basins• Significant difference between GOV and BAU

CCM3/IBIS/THMB coupled

GOVBAU

• Madeira and Tocantins have largest deforestation (GOV = 41%, 80%) • Net positive change - local ET decrease is larger

CCM3/IBIS/THMB coupled

• Tocantins and Xingu have similar precipitation decrease (GOV = -15%)• Xingu is less deforested (25% vs 80%)

CCM3/IBIS/THMB coupled

• 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%?)

Synthesis

GOV BAU

2. 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

Original Questions

3. 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

Original Questions

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.

Xingu 66% deforested20% precipitation decrease17% discharge decrease

CCM3/IBIS/THMB coupled BAU 2050

Xingu 66% deforested20% precipitation decrease17% discharge decrease

Tocantins/Araguaia93% deforested14% precipitation decrease 8% discharge increase

CCM3/IBIS/THMB coupled BAU 2050

IBIS/THMB alone – the effect of modern deforestation