Key sources of uncertainty in forest carbon inventories

Raisa Mäkipää withMikko Peltoniemi, Suvi Monni, Taru Palosuo,

Aleksi Lehtonen & Ilkka Savolainen

EU Workshop on Uncertainties in Greenhouse Gas Inventories 5-6 September 2005 Helsinki, Finland

• GHG reporting under the UNFCCC and Kyoto Protocol (KP)

• IPCC guidance for GHG reporting– 1996 revised guidelines– 2003 GPG for LULUCF sector (other sectors

already in 2000)– 2006 under expert review (from Sept 12)

Introduction

KP ->Need to improve inventories

• Completeness: all pools to be included• Consistency: time-series 1990-present• Transparency: default values, reporting• Accuracy: uncertainty analysis help to

priroritise efforts to improve inventories; uncertainty to be reduced as far as practicable

Inventories

• Land-use change– methods (sampling based NFI, remote sensing, land-

use statistics)– categories (definitions vs. monitroing system)– challenges e.g. initial C stocks and time of transition

• Forest remaining forest, major C stock and sink of LULUCF sector

Biomass carbon inventories

• Default method: Growth – Drain

• Stock change method: Stock t+1 – Stock t

Uncertainty analysis

• Guidance by IPCC GPG Chapter 5.2 Identifying and quantifying uncertainties

1. Error propagation equations

2. Monte Carlo Analysis

Error propagation equationsUncertainty of a product of several quantities

2n

22

21total U...UUU

where:

Utotal : the percentage uncertainty in the product of the quantities (the 95% confidence interval divided by the total and expressed as a percentage). Note that this uncertainty is twice the relative standard error (in %), a commonly used statistical estimate of relative uncertainty.

Ui :the percentage uncertainties associated with each of the quantities.

(Equation 5.2.2, IPCC GPG 2004)

Uncertainty of biomass stock estimates

222V BEFdstock UUUU

can be one valuewhere:

Uv : uncertainty of the volume

Ud : uncertainty of the wood density

UBEF : uncertainty of BEF

vGU

Relative standard error (rstock) and percentage uncertainty of biomass stock of spruce for Svealand (%)

Age rvol rBEF rstock %Uncertainty (2*rstock)

11-20 11 21 24 4821-30 9 10 13 2631-40 7 7 10 2041-60 6 4 7 1461-80 6 3 7 1481-100 8 3 9 18101-120 9 3 9 18121-140 12 5 13 26141- 16 3 16 32

Measure used in NFIsUsed by

IPCC GPG

Uncertainty of a sum of several quatities

n21

2nn

222

211

E EEE

EUEUEUU

where:

UE : percentage uncertainty of the sum

Ui : percentage uncertainty associated with source/sink i

Ei : emission/removal estimate for source/sink I

(Equation 5.2.1, IPCC GPG 2004)

Uncertainty of stock change: how stock estimates apply on sink assessment

12

21

22 )()(

12

timetime

timeStocktimeStock

eStockChang StockStock

StockUStockUU timetime

Could give for uncertainty of the change in biomass stock (example with illustrative values)

11501200

)1150%25()1200%25( 22

eStockChangU

Soil GHG inventory

• Peatlands based on flux measurements – area * emission factor

• Upland forest soils – change in C stock

Methods to assess change in soil C stock

1. Repeated measurements2. Statistical models on soil C as a function of

stand and tree parameters3. Dynamic soil model integrated to NFI data on

forest resources

Differences in uncertainty assessment??

Uncertainty analysis

• IPCC GPG Ch 5.2 Identifying and quantifying uncertainties

1. Error propagation equations

2. Monte Carlo Analysis

• Aggregated or averaged input data on – growing stock, area (forest land, no peat), growth

indices, harvests, temperature, natural mortality

• Annual estimates of growing stock interpolated from the estimates at calculation period ends (GSstart, GSend) using growth indices and drain estimates

• Integrated with dynamic soil C model

An inventory based carbon model combining a dynamic soil component

Methods to estimate uncertainties and key factors:

Approach 2 - Monte Carlo

X =

1

P1

1

P2

1

Result

X = Any operator

Pi,j = Any parameter, input or variable in the system

Laskennan kulku

Model for litter of

understoryvegetation

Inventory: stand volume

BEFs

Errors of living biomasses by component

Errors of biomass turnover rates

Errors in the amounts of litter for three different litter types (input to the soil model)

Inventory: Area

Drain statistics

Error of drain biomass (harvest residues)

Errors of source data and models

The result distributions for the amount of soil carbon, changes in carbon, soil respiration

Errors related to the parameters in the soil model

stem, branches, roots, etc..

Underst. litter production

Extractives

CelluloseFine

woody

Coarse woody

Lignin-like

Humus 1

Humus 2

CO2

CO2

CO2

CO2

CO2

Carbon stocks in 1990 (Tg)

Vegetation C stock 1998 (Tg)

De

nsi

ty

540 560 580 600 620 640

0.00

00.

005

0.01

00.

015

0.02

00.

025

Min. 538.21st Q. 580.3Med. 590Mean 590.33rd Q. 600.1Max. 648.9SD. 14.8

Soil C stock 1990 (Tg)

De

nsi

ty

1000 2000 3000 4000 50000

e+00

4

e-04

8

e-04

Min. 309.81st Q. 786.2Med. 1044Mean 11743rd Q. 1422Max. 5282SD. 550.9

Forest C stock 1990 (Tg)

De

nsi

ty

1000 2000 3000 4000 5000 60000

e+00

4

e-04

8

e-04

Min. 876.21st Q. 1376Med. 1634Mean 17653rd Q. 2013Max. 5895SD. 552

Vegetation Soil Forest total

CV~ 2.5%

CV~ 47%

CV~ 32%

Carbon sinks in 1990 (Tg)

Soil C sink 1990-1989 (Tg)

De

nsi

ty

-5 0 5 10 15 20

0.00

0.05

0.10

0.15

Min. -5.81st Q. 4.5Med. 6.3Mean 6.43rd Q. 8.2Max. 20SD. 2.8

Forest C sink 1990-1989 (Tg)

De

nsi

ty

5 10 15 20 25

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Min. 1.51st Q. 12Med. 13.9Mean 143rd Q. 15.9Max. 27.6SD. 2.9

Vegetation C sink 1990-1989 (Tg)

De

nsi

ty

4 5 6 7 8 9 10

0.0

0.1

0.2

0.3

0.4

0.5

Min. 4.21st Q. 7Med. 7.6Mean 7.63rd Q. 8.1Max. 10.7SD. 0.8

Vegetation Soil Forest total

CV~ 8%

CV~ 43%

CV~ 21%

1990 1992 1994 1996 1998 2000 2002

05

1015

Vegetation

Year

Ca

rbo

n s

ink

(Tg

)

1990 1992 1994 1996 1998 2000 2002

-50

510

Upland soils

Year

Ca

rbo

n s

ink

(Tg

)

2.5% C.l.25%50%75%97.5%

Uncertainty of C sink

Key factors of uncertainty: vegetation sink and stock

0

0.2

0.4

0.6

0.8

Ap

pro

x. co

ntr

. to

vari

an

ce

Veg C sink 1990-1989Veg. C stock 1990

0

0.2

0.4

0.6

0.8

1

Ap

pro

x. co

ntr

. to

vari

an

ce

Soil C sink 1990-1989Soil C stock 1990

The key factors of uncertainty: soil sink and stock

Combined effectin the 1st run

-40 -20 0 20 40 60 80

Tg CO2-eq

1990

2003

Fuel combustion

Fugitive emissions

Industrial processes

Agriculture

Waste

Forest biomass

Forest soil

Other LULUCF categories

CO2 emissions and removals, error bar is 95% CI

Summary

• Soil C sink can be estimated with a dynamic soil C model; input derived from biomass data provided by NFI

• Complete inventories incl. all pools needed• LULUCF contribute notably to overall uncertainty of the

GHG inventory• Error propagation equations are OK for uncertainty

analysis of carbon sink of biomass• Soil carbon model -> MonteCarlo analysis• Soil model parameters determine most of the uncertainty

of forest/soil stocks.• Variables that are related changes contribute to the

uncertainty of forest sinks

Discussion: Reliability of results (1/2)

• Sources of uncertainty not covered in the study:– model structure: possible wrong or missing

components or processes?– classification/applicability of submodels to this case – forest inventories report average GS for a period, not

for a single year– The use of average climatic conditions for the soil

model instead of detailed data

Discussion: Reliability of results (2/2)

• Subjectivity of uncertainty estimates– Expert judgment needed for parameters

missing uncertainty estimates– What is included in the reported uncertainty

estimates varies

Discussion

• Estimation of annual sinks introduces extra input variables into the system

• Information on variability or correlation of model parameters lacks although the information could be available for input data– For some model parameters (eg. turnover rates)

potential variability should be treated as uncertainty because there is no data

The method is more applicable for the estimation of long term sinks

• Thank you!

• www.efi.fi/projects/uncertainty