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?