Assessing the Influences of Urbanization on Terrestrial Carbon Pools and Fluxes

Andy B. Reinmann and Lucy R. HutyraBoston University, Department of Earth & Environment

View of the Terrestrial Carbon Cycle

Carbon cycle research has centered on quantifying and understanding the controls on the terrestrial carbon sink in undeveloped landscapes

• Global urban expansion occurring at twice the rate of population growth• Tripling of urban land cover

from 2000-2030

• Developed land covers ~6% of contiguous U.S. land area• Twice the extent of northern

hardwood forest• Doubling of urban extent

from 2000-2030

• Urbanization is new face of land cover change

View of the Terrestrial Carbon Cycle

Seto et al. 2012 ; Nickerson et al. 2011

Projecting Land Cover Change from Urbanization

Projects housing development• 1 ha resolution across U.S. • 13 housing density categories • 5 population growth scenarios

EPA Integrated Climate and Land Use Scenarios (ICLUS)

ICLUS

Bierwagen et al. 2010

Projecting Land Cover Change from Urbanization

• Combine ICLUS with National Land Cover Database (NLCD) products

• Composition of each housing density category

• Proportions used to infer land cover change from ICLUS projections

ICLUS NLCD

Projecting Changes in Carbon Storage and Fluxes

• USFS Forest Inventory and Analysis• Forest growth curves• Forest biomass• Harvesting patterns

• Biomass removed from harvesting and development divided into 9 carbon turnover pools

• Published urban biomass values (Raciti et al. 2012)

Massachusetts-Specific Parameters• Forest and Urban are most

common land cover types• Inversely related

• Approach is an empirically informed, bookkeeping and scenario analysis• NOT a process-based model

Prop

ortio

n of

Tot

al A

rea

Housing Density Category

Historical Changes in MA Forest Cover

Agricultural Expansion

Reforestation

Urban Expansion

Projected Changes in MA Forest Cover

• 1971-2010 (observed)• 0.22% yr-1 decline

• 2010-2050 (projected)• 0.07 to 0.27% yr-1 decline

Projected Changes in MA Forest Cover

• 1971-2010 (observed)• 0.22% yr-1 decline

• 2010-2050 (projected)• 0.07 to 0.27% yr-1 decline

• MA pop. growth rate is 0.31% yr-1 • US mean is 0.97% yr-1

• Global mean is 1.29% yr-1

US Census; UN Population Division

• Forest cover decreases west to east (Inverse of population patterns)

• Lowest forest losses in most rural counties, losses increase from west to east

Projected Spatial Distribution of Forest Cover

20-30%

40-50%

50-60%

60-70%

70-80%

80-90%

2010 Forest Cover

B1 (Low Pop. Growth) 2010-50

A2 (High Pop. Growth) 2010-50

<10%

10-20%

20-30%

30-40%

Forest Loss

<10%

10-20%

20-30%

30-40%

Forest Loss

Boston

Conserved/UndevelopableStable > 50% Forest Cover

Stable Urban> 25% Loss of Forest Cover

Changes in Spatial Distribution of Forest Cover 2010 to 2050

Terrestrial Carbon Fluxes 2010 to 2050

• B1 (Low pop. growth)• Forest carbon sink

offsets emissions from land conversion

• A2 (High pop. growth)• Land conversion

becomes net source in rapidly urbanizing counties

• Land conversion reduces forest C sink by up to 28%

Loss

to a

tmos

pher

eU

ptak

e by

veg

.

Briber et al. (in review)

Urban growing conditions in aggregate favor vegetation growth (at least in MA)

Terrestrial Carbon Fluxes 2010 to 2050

• Urban biomass accrual up to 75% of terrestrial C sink in rapidly developing landscapes

• Potential to offset reductions in C storage from forest loss

• Importance increases with urbanization

Loss

to a

tmos

pher

eU

ptak

e by

veg

.

Terrestrial Carbon Fluxes 2010 to 2050

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• Assuming constant per capita rate of emissions

• Emissions from land cover change < 2% of total emissions

• Rural emissions offset by terrestrial carbon sink

• MA terrestrial carbon sink projected to offset 10 to 12% of fossil fuel emissions Lo

ss to

atm

osph

ere

See Gately et al. poster on fossil fuel emissions

Terrestrial Carbon Fluxes 2010 to 2050

SummaryUrbanization has a profound affect on the terrestrial C cycle• Rapid decline in MA forest cover; urban biomass can comprise a large proportion

of the terrestrial C sink

• Terrestrial C sink will offset emissions associated with urbanization, but will be less than 12% of MA fossil fuel emissions

• Most of our future urban area does not yet exist, we can actively shape the patterns in C fluxes through development choices

• Urban biosphere fluxes also vital for atmospheric inversions and GHG verification

Ongoing & Future directions• Process-based modeling (e.g., Hardiman et al. poster)

• Albedo and latent heat flux

• Quantify uncertainty

• Export to other states (Gradient of land cover types and urbanization trajectories)

Acknowledgements

Special Thanks to:Britt Briber, Tori Dearborn, Conor Gately, Jackie Getson, Brady Hardiman

Funding Sources: