Transcript Simulating Throughfall Exclusion Experiments in Amazonia

Simulating the Caxiuanã Throughfall
Exclusion Experiment with JULES
David Galbraith, University of Oxford
Images courtesy of Antonio Carlos Lola da Costa
Talk Structure
• 1) An introduction to JULES and how it
simulates drought impacts on vegetation.
• 2) Preliminary results of simulations of the
throughfall exclusion experiment in Caxiuanã.
Land surface processes simulated by JULES
Graphic from Bonan et al. 2008
• JULES: Joint UK Land Environment Simulator;
• Based on MOSES land surface model (embedded within HadCM3 climate model)
TRIFFID – Vegetation Dynamics
Change in Biomass
‘Spreading term’
NPP
Litterfall
Change in Fractional Cover of PFTs: Lotka-Volterra
• JULES run in combination with TRIFFID (Cox 2001) for simulation of
vegetation dynamics.
• Individual gridcells divided into 9 surface types, including 5 plant
functional types (Broadleaf tree, needleleaf tree, C3 grass, C4 grass,
shrub).
• Energy balance, water budget, carbon budget, etc. computed separately
for each PFT/tile.
Drought Physiology in JULES
Cox et al. 1998
Collatz et al. 1991,,1992
A
θw
θc
Soils in JULES
10 cm
25 cm
65 cm
• 4 soil layers; default soil depth: 3m
• PFTs differ in rooting depth – default for
broadleaf trees is 3 m
• Root distribution follows an exponential
decline profile with depth
• β stress factor is weighted by the
fraction of roots in each layer
• Soil hydraulics following Clapp & Hornberger (1978)
2m
• b, ks and ψs are estimated based on soil texture
Using JULES to simulate Amazonian TFEs:
Experimental Protocol
• All runs spun up from bare ground, and pre-industrial CO2
(spin-up period of ~ 100 years sufficient to equilibrate
vegetation and soil carbon pools).
• Following spin-up, ‘transient period’ (1860 – start of
observational period) where CO2 increases annually
according to observations.
• Met data recycled throughout spin-up and transient
periods.
• Observational Period (2001-2008 (Caxiuanã); 20002005(Tapajós)). Rainfall reduced by 50% at the beginning
of the TFE treatment (2002 in Caxiuanã, 2000 in Tapajós).
Simulation Results: Pre-Drought (2001) State
Variable
Modelled
Observed
Broadleaf tree cover (%)
83
100
Canopy height (m)
24.5
30-35 (reference)
Vegetation Carbon (t C ha-1)
156
200 - 240* (including coarse
roots, da Costa et al. 2010)
Leaf Area Index (m2 m-2)
6.55
5.5 (Fisher 2007)
GPP (t C ha-1 yr-1)
49.18
30-33 (Control Plot, Fisher
et al. 2007, Metcalfe et al.
2010b)
NPP (t C ha-1 yr-1)
9.03
10.6 (Control Plot, Metcalfe
et al. 2010b)
Carbon Use Efficiency (NPP/GPP)
0.18
0.32 (Control Plot, Metcalfe
et al. 2010b)
Soil Carbon (t C ha-1 yr-1)
29.12
47.0 (to 3 m, Quesada et al.
2008)
Heterotrophic Respiration (Soils)
(t C ha-1 yr-1)
9.0
10.2 (Metcalfe et al. 2010)
Simulation Results: Soil Moisture and Plant Water Stress
Annual Soil Moisture Dynamics
1600
Layer1(top)
Layer2
Layer3
Layer4(bottom)
Soil moisture content(mm)
1400
1200
1000
800
600
400
200
0
2001
2002
2003
2004
2005
2006
2007
2008
2006
2007
2008
Year
Soil Moisture Stress
Beta Soil Moisture Scalar
1
0.95
0.9
0.85
0.8
0.75
0.7
2001
2002
2003
2004
2005
Year
Simulation Results: Evapotranspiration v
Evapotranspiration dynamics
0.75
Mean Evaporation (kg m 2 s-1)
0.7
0.65
0.6
0.55
0.5
0.45
2001
Total evapotranspiration
Broadleaf tree transpiration
2002
2003
2004
2005
Year
2006
2007
2008
Simulation Results: Soil Carbon and Soil Respiration v
Soil Carbon
3.3
3.2
Soil Carbon(kg C m -2)
3.1
3
2.9
2.8
2.7
2.6
2.5
2001
2002
2003
2004
2005
Year
2006
2007
2008
Simulation Results: GPP and NPP
GPP and its primary components
50
45
Accumulated Annual Flux(t C ha -1 yr-1)
40
35
30
25
20
15
10
5
0
2001
GPP
NPP
Plant Respiration
2002
2003
2004
2005
Year
2006
2007
2008
Simulation Results: Components of Autotrophic Respirationv
Components of Plant Maintenance Respiration
16
Accumulated Annual Flux(t C ha -1 yr-1)
14
12
10
8
6
4
2001
Leaf Maintenance Respiration
Root Maintenance Respiration
Wood Maintenance Respiration
2002
2003
2004
2005
2006
2007
Year
Observed Leaf Respiration: 7.3 (Metcalfe et al. 2010)
Observed Fine Root Respiration: 6.2 (Metcalfe et al. 2010)
Observed Stem Respiration: 8.9 (Metcalfe et al. 2010)
2008
Simulation Results: Leaf Area Index and Vegetation Carbon
Leaf Area Index
Leaf Area Index(m 2 m -2)
7
LAI(JULES)
LAI(Observations)
6
5
4
3
2001
2002
2003
2004
2005
2006
2007
2008
2006
2007
2008
Year
Vegetation Carbon(kg C m -2)
Vegetation Carbon
20
18
16
14
12
10
8
2001
Vegetaion Carbon(JULES)
Vegetation Carbon(Observations)
2002
2003
2004
2005
Year
LAI Data = 20% drop in 2002-2003, sustained in 2007; Model: no change in 2002-2003, ~
30% reduction in 2007
Cveg Data: 20% loss of Cveg over 7 years of drought; Model: 34% loss, but only 10%
relative to pre-drought met data cycle
This version of JULES more sensitive to drought than
previous version of MOSES-TRIFFID
Galbraith et al. 2010
Sensitivity Analysis of Soil hydraulics &
Rooting Depth
18
16
Vegetation Carbon (kg C m-2)
14
12
10
10 m roots; new CH
10m roots; old CH
8
10 m roots; Harris
10 m roots; KM67 soil
6
3m roots;
4
2
0
1992
1994
1996
1998
2000
Year
2002
2004
2006
2008
Conclusions/Closing Thoughts
• JULES captures some of the trends
reasonably well (biomass, LAI)
• GPP and Plant respiration considerably higher
than observations
• This version of JULES more sensitive to
drought than other previous versions ... still
working out why