Assessing the Influences of Urbanization on
Terrestrial Carbon Pools and Fluxes
Andy B. Reinmann and Lucy R. Hutyra
Boston 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
View of the Terrestrial Carbon Cycle
• 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
Seto et al. 2012 ; Nickerson et al. 2011
Projecting Land Cover Change from Urbanization
ICLUS
EPA Integrated Climate
and Land Use Scenarios
(ICLUS)
Projects housing development
• 1 ha resolution across U.S.
• 13 housing density categories
• 5 population growth scenarios
Bierwagen et al. 2010
Projecting Land Cover Change from Urbanization
ICLUS
NLCD
• 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
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
Agriculture
Water
Urban/Developed
Other
0.2
0.4
0.6
0.8
1.0
• Approach is an empirically informed,
bookkeeping and scenario analysis
• NOT a process-based model
0.0
Proportion
TotalArea
Area
Proportion of Total
• Forest and Urban are most
common land cover types
• Inversely related
1
2
3
4
5 6 7 8 9 10 11 12 13 99
Housing Density
Category
Housing
Density
Category
90
Historical Changes in MA Forest Cover
80
Reforestation
70
60
50
40
Agricultural Expansion
FIA (Historical)
30
MA % Forested
Urban Expansion
1600
1675
1750
1825
Year
1900
1975
2050
90
Projected Changes in
MA Forest Cover
70
60
50
40
FIA (Historical)
B1 (Low)
BC (Baseline)
A2 (High)
30
MA % Forested
• 2010-2050 (projected)
• 0.07 to 0.27% yr-1 decline
80
• 1971-2010 (observed)
• 0.22% yr-1 decline
1600
1675
1750
1825
Year
1900
1975
2050
7
6
5
4
3
1950
2000
2050
40
50
60
hist.pop[, 3]
FIA (Historical)
B1 (Low)
BC (Baseline)
A2 (High)
Population (Historical)
1600
1675
1750
1825
Year
US Census; UN Population Division
Population (millions)
FALSE
70
1900
30
• MA pop. growth rate is
0.31% yr-1
• US mean is 0.97% yr-1
• Global mean is 1.29% yr-1
MA % Forested
• 2010-2050 (projected)
• 0.07 to 0.27% yr-1 decline
80
• 1971-2010 (observed)
• 0.22% yr-1 decline
8
90
Projected Changes in
MA Forest Cover
1900
1975
2050
Projected Spatial
Distribution of Forest Cover
2010 Forest Cover
Boston
20-30%
60-70%
40-50%
70-80%
50-60%
80-90%
• Forest cover decreases west to east
(Inverse of population patterns)
B1 (Low Pop. Growth) 2010-50
• Lowest forest losses in most rural
counties, losses increase from west
to east
Forest Loss
<10%
20-30%
10-20%
30-40%
A2 (High Pop. Growth) 2010-50
Forest Loss
<10%
20-30%
10-20%
30-40%
Changes in Spatial Distribution of Forest Cover
2010 to 2050
Conserved/Undevelopable
Stable > 50% Forest Cover
Stable Urban
> 25% Loss of Forest Cover
Uptake by veg. Loss to atmosphere
0.5
0.0
A2 (High)
-0.5
Essex
Berkshire
MA
Essex
Berkshire
MA
• Land conversion reduces
forest C sink by up to 28%
B1 (Low)
-1.0
• A2 (High pop. growth)
• Land conversion
becomes net source in
rapidly urbanizing
counties
Development/Harvesting
Forest Biomass Accrual
Urban Biomass Accrual (only expansion)
C Flux (MgC ha-1yr-1)
• B1 (Low pop. growth)
• Forest carbon sink
offsets emissions from
land conversion
1.0
Terrestrial Carbon Fluxes 2010 to 2050
Terrestrial Carbon Fluxes 2010 to 2050
40
30
20
Steet
Trees
Urban
patch
PreUrban
10
BAI (cm2 yr-1)
50
Urban growing conditions in aggregate
favor vegetation growth (at least in MA)
Briber et al. (in review)
?
?
?
?
Essex
MA
Essex
Berkshire
Berkshire
?
?
Uptake by veg. Loss to atmosphere
0.5
A2 (High)
0.0
B1 (Low)
MA
• Importance increases
with urbanization
Development/Harvesting
Forest Biomass Accrual
Urban Biomass Accrual (only expansion)
Urban Biomass Accrual (expansion and 2x growth rate)
-0.5
• Potential to offset
reductions in C storage
from forest loss
-1.0
• Urban biomass accrual
up to 75% of terrestrial
C sink in rapidly
developing landscapes
C Flux (MgC ha-1yr-1)
1.0
Terrestrial Carbon Fluxes 2010 to 2050
25
Terrestrial Carbon Fluxes 2010 to 2050
15
A2 (High)
Loss to atmosphere
10
Essex
Berkshire
MA
Essex
Berkshire
MA
• MA terrestrial carbon sink
projected to offset 10 to
12% of fossil fuel emissions
B1 (Low)
5
• Rural emissions offset by
terrestrial carbon sink
Fossil Fuels
Development/Harvesting
Forest Biomass Accrual
Urban Biomass Accrual (only expansion)
Urban Biomass Accrual (expansion and 2x growth rate)
0
• Emissions from land cover
change < 2% of total
emissions
C Flux (MgC ha-1yr-1)
20
• Assuming constant per
capita rate of emissions
See Gately et al. poster on fossil fuel emissions
Summary
Urbanization 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
Funding Sources:
Special Thanks to:
Britt Briber, Tori Dearborn, Conor Gately, Jackie Getson, Brady Hardiman