Optimising ORCHIDEE simulations

at tropical sites

Hans Verbeeck

LSM/FLUXNET meeting June 2008, Edinburgh

LSCE, Laboratoire des Sciences du Climat et de l'Environnement - FRANCE

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Outline

Introduction Model: ORCHIDEE model Assimilation system: ORCHIS Temperate sites: results from

Santaren et al. Tropical sites: first results Conclusions

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

POLICE

Marie Curie project:

Parameter Optimisation of a terrestrial biosphere model to

Link processes to Inter annual variability of Carbon fluxes in

European forest Ecosystems

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

POLICE: goals

Increase knowledge about parameters

Variation between and within species (PFT’s)

Spatio-temporal variability of parameters

Validation of the model, model deficiencies

Improve the model’s performance

...

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

ORCHIDEE

ORganizing Carbon and Hydrology In

Dynamic EcosystEms

Process-driven global ecosystem model

Spatial: Developed for global applications

“grid point mode”

Time scales: 30 min – 1000’s years

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

ORCHIDEE

Meteorological forcing

PhotosynthesisTranspiration

Surface Energy budget

AutotrophicRespiration

Soil Moisture budget

Biophysical moduletime step: (half)hourly

Heterotrophic respiration

Allocation

Decomposition

Phenology

Mortality

Carbon dynamics moduletime step: daily

Output variables

Model Parameters

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

ORCHIDEE

13 Plant Functional Types (PFT’s) Standard parameterisation Specific phenology

Initial carbon pools Spinup runs (e.g. 500 years), until pools and fluxes

are at equilibrium

How to deal with spinup runs when optimising a model? New spinup run for each new parameter combinantion?

Using forest inventory data to optimise spinup runs?

Obs.+Errors

Y, R

Parametersand uncertainties

X, P

ModelORCHIDEE

M

Forward approach Modeled flux

M(X)

E(X) = M(X) - YInverse approach« minimize E »

Meteorological driversInitial

conditions

FCO2 (μmol/m2/s)

1 DAY 1 DAY

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Orchidee Inversion System

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Orchidee Inversion System

Bayesian optimisation approach

Prior info on parameters (standard values

+ uncertainties PDF)

Data + uncertainties

Cost function

BFGS algorithm

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Data•Fluxes:

• Carbon

• Latent Heat

• Sensible Heat

• Net Radation

• Only real data

• Errors on the data (PDF)

• Gaussian

• σ=15% (day),

30% (night)

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Cost Function

)()()()(2

1)( 11

bbt

bt xxPxxxHyRxHyxJ

Mismatch between model and observed fluxes

Mismatch between a priori and optimised parameters

Covariance matrices containing a priori uncertainties on

parameters and fluxes and error correlations

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

BFGS algorithm

Gradient based: calculates gradient at each time

step (method of finite differences)

Takes into account lower and upper bound of

each parameter

Minimum reached: curvature, sensitivity,

uncertainties and correlations between

parameters are calculated

1 year 1 year 1 year 1 year

AB

(97

-98)

BX

(97

-98)

TH

(98

-99)

WE

(98

-99)

FCO2 (gC/m2/Day) FH2O (W/m2)

A priori Model

Optimised Model

Observations

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Santaren et al. GBC 2007

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Results & problems

Preliminary results show that this is a promising aproach

Assimilating 3 weeks of summer data:

Improves diurnal fit

Diurnal fit for rest of growing season is not so good seasonality

Should we vary parameters with time? Yearly, monthly, ...

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Results & problems

Same results could be obtained when only NEE and λE observations were included

Photosynthesis parameters are well constrained

Respiration parameters can not be robustly determined. High

dependence on initial carbon pools.

Assimilate NEE, λE, GPP, Reco, ...?

How to constrain the pools?

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Guyana

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Santarem km 67

Parameter optimisation vs. Model structure improvement?

Saleska et al. Science, 2003

Wet Dry

Drought response

GPP: weak

R: strong

Unexpected seasonality dominated by moisture effects on respiration

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Santarem km 67

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Santarem km 67: GPP and Reco

Should we only use “real measured fluxes” or also GPP and Reco? Equifinality?

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Santarem km 67: soil depth

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Santarem km 67: soil water stress

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Conclusions

Possibilities to include forest inventory data: multiple constraint approach? (C pools, spinup runs,...)

How to modify the cost function to assimilate data on different time scales?

How much data are needed?

Introduction ORCHIDEE ORCHIS Temperate sites Tropical sites Conclusions

Conclusions

Temporal variation of parameters?

Optimal parameter value vs. biological significance? Model structure?

How to deal with uncertainty on the measured fluxes? Should we take correlation between uncertainties into account?

Use of GPP and Reco?

Thanks to: Philippe Peylin, Diego Santaren, Cédric

Bacour, Philippe Ciais

Data at tropical sites: PIs from Guyana and Brazilian sites

Thank you!