Impact of climate uncertainty upon trends in outputs

generated by an ecosystem model

Adam Butler & Glenn Marion, Biomathematics & Statistics Scotland

•

Ruth Doherty, Edinburgh University•

Jonathan Rougier,University of DurhamProbabilistic Climate Impacts workshop,

September 2006

Some backgroundSome background

AimsTo quantify uncertainties in projections of global and regional vegetation trends for the 21st century from the LPJ ecosystem model, based on future climate uncertainty

BIOSSPublic body providing quantitative consultancy & research to support biological science

Funded by ALARM: a 5 year EU project to assess risks of environmental change upon European biodiversity

The LPJ Ecosystem ModelThe LPJ Ecosystem Model

“The Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ) combines process-based, large-scale representations of terrestrial vegetation dynamics and land-atmosphere carbon and water exchanges in a modular framework…”

http://www.pik-potsdam.de/lpj/

Fluxes(daily)

VegetationDynamics (annual)

Drivers

LPJ-Lund Potsdam Jena LPJ-Lund Potsdam Jena Vegetation ModelVegetation Model

Based on climate and soils inputs LPJ simulates:Vegetation dynamics and competition amongst 10 Plant Functional Types (PFTs)Vegetation and soil carbon and water fluxes

Average grid-cell basis with a 1-year time-step

Spin-up period of 1000 years to develop equilibrium vegetation and soil structure at start of simulation

LPJ-Lund Potsdam Jena LPJ-Lund Potsdam Jena Vegetation ModelVegetation Model

Inputs:Soils: FAO global soils dataset: 9 types inc coarse-fine range (CRU)Climate: monthly temperature, precipitation, solar radiation

CO2: provided for 1901-1998; updated to 2002 from CDIAC

Model output scale determined by driving climate

Acknowledgements:LPJ code- Ben Smith, Stephen Sitch, Sybil SchapoffCRU data- David Viner (CRU), GCM data (PCMDI)

Tropical Broadleaf Evergreen Tree (FPC)Tropical Broadleaf Evergreen Tree (FPC)

C3 Grasses (FPC)C3 Grasses (FPC)

LPJ Model UncertaintyLPJ Model Uncertainty

Model inputs: future climate uncertainty

Representation of mechanisms driving model processes (Cramer et al. 2001; Smith et al. 2001- tests different formulations of relevant processes)- generally use most up-to date formulations from literature

Parameters within the model (Zaehle et al. 2005, GBC)

Zaehle et al. 2005Zaehle et al. 2005Latin hypercube sampling

Assume uniform PDF for each parameterExclude unrealistic parameter combinations

Simulations at sites representing major biomes (81)

400 model runs (61-90 CRU climatology and HadCM2 1860-2100)

Identified 14 functionally important parametersDifferences in parameter importance in water-limited regionsEstimated uncertainty range of modelled results:

61-90: NPP=43.1 –103.3 PgC/yr; cf. 44.4-66.3 Cramer et al. (2001)

Zaehle et al (2005)Zaehle et al (2005)

NBP = NEE+BiobUc=full uncertainty rangeC=excluding unrealistic

parametersNPP accounting

for parameter uncertainty

Increases in 2050s due

to increased CO2 and

WUE, thereafter a

decline

Parameter uncertainty

increases in the future

Uncertainty estimates in

NBP/NPP comparable to

those obtain from

uncertainty amongst 6

DGVMs

Future Climate Uncertainty Future Climate Uncertainty based onbased on

IPCC 4IPCC 4thth Assessment GCM Assessment GCM simulationssimulations

IPCC-AR4 simulationsIPCC-AR4 simulations

GCMs contributing to SRES A2GCMs contributing to SRES A2

COCO22 concentrations concentrations

Investigating the effect of Future Investigating the effect of Future Climate Uncertainty for Climate Uncertainty for

LPJ predictions LPJ predictions

Perform 19 separate runs of LPJ at the global scaleone run using CRU data for 1900-2002 at 0.5o x 0.5o

results from 18 simulations from 9 GCMs for the period 1850-2100 (20th Century and A2) running at the native scale of each GCM

GCMs with multiple ensemblesCCCMA-CGCM3, MPI-ECHAM5, NCAR-CCSM3

GCMs with single ensemble memberCNRM-CM3, CSIRO-MK3, GFDL-MK2, MRI-CGCM2-3, UKMO-HADCM3, UKMO-HADGEM

Global mean temperature anomalyGlobal mean temperature anomaly relative to 61-90 relative to 61-90

Net Primary Production

Net Ecosystem Production

Plant Functional Type

Heterotrophic respiration

Vegetation carbon

Soil carbon

Fire carbon

Run-off

Evapotranspiration

For each grid cell LPJ produces annual values for:

LPJ OutputsLPJ Outputs

…we focus on globally averaged values of these variables…

Net Primary Production

Net Ecosystem Production

Plant Functional Type

Heterotrophic respiration

Vegetation carbon

Soil carbon

Fire carbon

Run-off

Evapotranspiration