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Die-back of the Amazon in DGVMs: climate drivers and mechanisms
David Galbraith, Patrick Meir, Peter Levy, Daniel Metcalfe
What is the best use of Biosphere 2?March 06, 2009
White and Friend (1999)
Amazon Die-back Predictions: A Brief History
Cox et al. (2000)
Sitch et al. (2008)
Uncertainty in Modelled Die-back
ECOSYSTEM RESPONSE
EMISSIONS
CLIMATE RESPONSE
PARAMETERS
PROCESSES
Carbon Cycle Feedbacks
Aims
1) Separate the contributions of four environmental variables to Amazon dieback in 3 DGVMs:
• precipitation• relative humidity• temperature • carbon dioxide
2) Identify which carbon cycle process responses most affect the simulated loss of Amazon vegetation carbon in different models?
• Direct effect on Plant respiration• Direct effect on GPP • Indirect effect on GPP
Modelling Protocol
3 DGVMS (HYLAND, LPJ, TRIFFID) + IMOGEN GCM ANALOGUE
4 IPCC SCENARIOS
16 Factorial Simulations per model/scenario
combination
Predicted Change in Vegetation C in 2100
Simulations with CO2 held constant
A1FI Precipitation Only
A1FI Temperature Only
A1F1 except CO2
HYLAND LPJ TRIFFID
Predicted Change in Vegetation C to 2100
A1F1 Precipitation + CO2
A1F1 Temperature + CO2
A1F1 Scenario
Simulations with varying CO2
HYLAND LPJ TRIFFID
Contributions of Environmental Drivers to Dieback
HYLAND
A1F1 A2 B1 B2
Ch
ang
e in
Am
azo
n V
eget
atio
n C
arb
on
(P
gC
)
-100
-80
-60
-40
-20
0
20
40
HYLAND
A1F1 A2 B1 B2
Ch
ang
e in
Am
azo
n V
ege
tati
on
Car
bo
n (
Pg
C)
-100
-80
-60
-40
-20
0
20
40
LPJ
A1F1 A2 B1 B2
Ch
an
ge
in
Am
azo
n V
eg
eta
tio
n C
arb
on
(P
gC
)
-100
-80
-60
-40
-20
0
20
40
TRIFFID
A1F1 A2 B1 B2C
ha
ng
e in
Am
azo
n V
eg
eta
tio
n C
arb
on
(P
gC
)-100
-80
-60
-40
-20
0
20
40
LPJ
A1F1 A2 B1 B2
Ch
an
ge
in
Am
azo
n V
eg
eta
tio
n C
arb
on
(P
gC
)
-100
-80
-60
-40
-20
0
20
40
TRIFFID
A1F1 A2 B1 B2
Ch
an
ge
in
Am
azo
n V
eg
eta
tio
n C
arb
on
(P
gC
)
-100
-80
-60
-40
-20
0
20
40
Precipitation CO2 RH Temperature
Contribution of environmental drivers to Amazon VegC loss in 4 IPCC scenarios
Response Curves of Amazonian Veg C to Precipitation
0 10 20 30 40 50 60 70 80 90 100-15
-10
-5
0
Precipitation Reduction(%)
G
PP
(PgC
)
0 10 20 30 40 50 60 70 80 90 100-10
-8
-6
-4
-2
0
Precipitation Reduction(%)
N
PP
(PgC
)
0 10 20 30 40 50 60 70 80 90 100-120
-100
-80
-60
-40
-20
0
Precipitation Reduction(%)
V
eget
atio
n C
arbo
n (P
gC)
0 10 20 30 40 50 60 70 80 90 100-30
-20
-10
0
10
20
Precipitation Reduction(%)
S
oil C
arbo
n (P
gC)
0 10 20 30 40 50 60 70 80 90 100-100
-80
-60
-40
-20
0
Precipitation Reduction(%)
Tr
ee C
over
(%)
0 10 20 30 40 50 60 70 80 90 100-100
-80
-60
-40
-20
0
Precipitation Reduction(%)
av
aila
ble
soil
moi
stur
e (%
)
HYLAND
LPJ
TRIFFID
Temperature Mechanisms
Lloyd and Farquhar 2008
Temperature Mechanisms: Results
Similar outcome, yet very different mechanisms
0
10
20
30
40
50
60
70
80
Lo
ss o
f Ve
ge
tatio
n C
arb
on
(P
gC
)
HYLAND LPJ TRIFFID
Direct Effect on PhotosynthesisDirect Effect on RespirationIndirect Effect via VPD
Temperature Mechanisms: Results (2)
0 5 10 15 20 25 30 35 40 45 500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Temperature(°C)
no
rma
lise
d r
ate
of n
et p
ho
tosy
nth
esi
s
HYLAND
LPJ
TRIFFID
2010 2020 2030 2040 2050 2060 2070 2080 2090 21000
20
40
60
80
100
120
Year
Am
azo
nia
n V
eg
eta
tion
Ca
rbo
n (
Pg
C)
Standard LPJLPJ(NPP=GPP/2.0)MOSES TRIFFID v. 1.0TRIFFID-JULES
How reliable are current DGVM processes?
• Which photosynthesis temperature dependency is correct?
• How plastic are temperature response curves to photosynthesis?
• How important are direct vs. indirect effects of temperature on photosynthesis?
• How should we represent plant respiration under changing climate?
Soil
moi
stur
e 0-
3 m
(m
m)
400
600
800
2002 2003 2004 2005 2006 2007
Eco
syst
em f
olia
r re
spir
atio
n(t
C h
a-1 y
r-1)
2
3
4
5
6
7
2002 2003 2004 2005 2006 2007
Lea
f d
ark
res
pira
tion
(m
ol m
-2 s
-1)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Lea
f da
rk r
espi
rati
on(n
mol
g-1
s-1
)
2
3
4
5
6
7
8
ControlTFE
Rai
nfal
l(m
m d
ay-1
)
30
60
90
Metcalfe, Meir et al.
Functional Diversity in Climate Change Responses in DGVMs
- How much variability is there in rainforest species sensitivity to drought/temperature?
- Which mechanisms dictate the outcome of plant competition under drought and increasing temperatures?
- Below-ground adaptation strategies – which processes are the most important?