Using Land Use Change Models to Assess Biophysical and

Biogeochemical Consequences: The Future is Not Like the Past

• R. DeFries,

[rd63@umail.umd.edu]• Department of Geography and Earth System Science Interdisciplinary Center,

University of Maryland College Park

L. Bounoua, Dept. of Meteorology, UMD and Goddard Space Flight Center

Land Use Change Models

Human Drivers of Land Use Change

Biophysical/Biogeochemical Consequences of Land Cover Change

Sustainability

Consequences of Land Cover Change for Ecosystem Services:

• Net primary productionglobal terrestrial carbon model (CASA)

• Surface climatecoupled land surface-general

circulation model (SiB2-CSU GCM)

#1: What are the consequences of anthropogenic land cover change for net primary production and surface climate at regional and global scales?

#2: How might consequences of future land cover change differ from the past?

#3: How do the effects from land cover change compare with interannual variability?

Undisturbed (derived from Matthews, 1983)

Existing (DeFries and Townshend, 1994)

2050 Future (derived from IMAGE 2.0)

Broadleaf evergreen forestBroadleaf deciduous forestMixed forestConiferous forestNeedleleaf deciduous forestWooded grasslandGrasslandShrubs and bareTundraBareCroplandIce

% Difference in Net Primary Production(existing - undisturbed land cover)

NPP loss NPP gain

% Difference in Net Primary Production(future - existing land cover)

NPP loss NPP gain

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Average NPP Difference

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Average NPP DifferenceL

atit

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Land cover changeInterannual variability in 1980s

Undisturbed to existing land cover Existing to future land cover

IS EFFECT OF ANTHROPOGENIC LAND COVER CHANGE ON NPP SIGNIFICANT

RELATIVE TO INTERANNUAL VARIABILITY?

Land cover change affects surface climate through:

• Morphologyalbedo

surface roughness

• Physiologyevapotranspiration

balance between sensible and latent heat flux

General increase in albedo (cooling) and decrease in latent heat flux (warming) with land use change

Hansen et al., 1995, Climate Forcings in the Industrial Era, PNAS.

Govindasamy et al., 2001, Land use change and Northern Hemisphere cooling, GRL.

Bonan, 1999, Frost followed the plow: Impacts of deforestation on the climate of the United States, Ecological Applications.

Shukla et al. 1990, Amazonian deforestation and climate change, Science.

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Surface Temperature Difference (C)

Land cover changeModelled interannual variability in 1980s

winter summer

IS EFFECT OF FUTURE ANTHROPOGENIC LAND COVER CHANGE ON CLIMATE

SIGNIFICANT RELATIVE TO INTERANNUAL VARIABILITY?

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Surface Temperature Difference (C)

future cooling future warmingfuture cooling future warming

#1: What are the consequences of anthropogenic land cover change for net primary production and surface

climate at regional and global scales?

• Depends on type of land cover conversion

• Large regional disparities

• Temperate conversion: increase in NPP, surface cooling

• Tropical conversion: decrease in NPP, surface warming

• Global averages mask regional differences

#2: How might consequences of future land cover change differ from the past?

• Past conversions predominantly in temperate regions for mechanized agriculture

• Future conversion likely to be predominant in tropics

• Predominant effect in future likely to be opposite in sign to past

#3: How do the effects from land cover change compare with interannual

variability?

• Consequences of past land cover change mostly within decadal-scale interannual variability

• Consequences of future changes outside of interannual variability

The past is not prologue to the future

1986 1996

50 km

Deforestation in Southern Bolivia