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

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

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

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

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

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…

Land Cover Change and Tocantins -- Costa et al., 2003 2000 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 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

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

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 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

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

Land cover changes affect the energy and water balance -- at two scales Regionally – Global and regional climate models suggest that when large enough (~> 100000s 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

Albedo difference is large. Upper Xingu

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

Land cover changes affect the energy and water balance -- at two scales Regionally – Global and regional climate models suggest that when large enough (~> 100000s 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

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

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.

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

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?

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

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 CTL Predominantly tropical evergreen forest and Cerrado MOD pasture and agriculture have replace 15% of native vegetation 2 simulations with prescribed historical climate 1939-2000 and different land cover Any difference in simulations is function of land cover change alone

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

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

Tocantins River – 1990s Observed -- black Achieve agreement with observations only if observed deforestation is included NOTE: With potential vegetation simulations 1949-2000 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

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

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 1939-2000 and different land cover Any difference in simulations from CTL is a function of land cover change alone

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

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

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

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

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

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%)

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

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

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

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.

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

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

IBIS/THMB alone – the effect of modern deforestation