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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
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
?
?
??
??
• 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)