Dynamic Modelling and its Usein Integrated Assessment Models

Maximilian Posch

Coordination Center for Effects(ICP M&M&, WGE)

RIVM/MNPBilthoven, The Netherlands

Effects-related Thresholds Used in IAM so far (1)

A. Critical Levels for Ozone: AOT40 for forests (10 ppm.h ) and crops (3 ppm.h) not dependent on location etc., ==> only exceedance mapping. B. Critical Loads of nutrient N (eutrophication) - single number per ecosystem - many numbers per grid - protection percentiles or average exceedances mapped.

Exceedance of CLnut(N) in 1980 and 2000

on 50x50 grid

Effects-related Thresholds Used in IAM so far (2)

C. Critical Loads of Acidity (S and N) - infinitely many CLs defining the CL function - many CL functions per grid - protection or average exceedance (AAE) mapped - protection and AAE isolines computed and used in IAM (optimisation).

Exceedance of acidity CLs for forests in 2000:

Grid average dep. Dep. to forests

Modifications since Gothenburg:

- Modifications to critical levels (fluxes; inclusion of site/grid-specific parameters (e.g. VPD)

- Update of critical loads (2003/2004)- separation of critical loads into ecosystem types (forests, waters, semi-nat. …)

… and exceedance calculations with concentrations/depositions that is

- on a 50x50 km2 grid and- ecosystem specific

Dynamic Modelling and Target Loads

Purpose of Dynamic Modelling (under the Convention):

Investigate time aspects (delay of damage and recovery) ofareas where critical loads were, are and will be exceededunder different deposition scenarios

- This cannot be done with Critical Loads!

Target Loads are one way to link dynamic model resultsto IAM.

Delay in Damage and Recovery:

Deposition

Delayedchemical response

Further delayedbiological response

What causes these delay times?

Finite buffers in the soil (irrelevant for steady state)

1. Cation exchangeCharacterised by Cation exchange capacity (CEC), i.e.the total amount of exchangeable base cations

2. (Additional) nitrogen sinks (immobilisation)Present immobilisation of N (much) larger than steady-state Ni

3. Sulphate ad/desorption(not everywhere)

Constraints for dynamic modelling under the LRTAP Convention:

- Emission reduction targets in Gothenburg Protocol have been derived with critical loads- CLs indicate where exceedances will remain after 2010- Dynamic models shall determine when recovery (or further damage) will occur

Thus:- Dynamic models have to be compatible with (updated) critical loads, i.e.- Dynamic models have to identify same areas as “exceeded” (risk of damage) and recovering (Dep<CL)

Target Loads (1)

Target Load (TL) =Deposition path (of S and N) for which a desired ecosystemstatus (e.g. Al/Bc=1) is reached in a pre-defined year(the target year) and maintained afterwards!

=> many TLs can be determined for a given ecosystem, depending on the choice of target year and the implementation of deposition reductions (policy options)

Critical Load (CL) =TL at steady state (infinite time horizon)

CL is an ecosystem property --a TL is not (but depends on ecosystem properties!)

Target Loads (2)

Deposition paths (of S and N):- we assume that deposition until 2010 is given (fixed): Gothenburg Protocol & NEC Directive …

- after N years (implementation period) the new deposition (target load) is kept constant (e.g. N=5 or 10)

- deposition decreases linearly during the implementation period

1960 1980 2000 2040 20602020

Protocol year

DM implementation year

DM target year 1

DM target year 2

Dep

ositi

on

Select (future) DepRun Model Al/Bc in target year = 1?Yes: TL=Dep; No:

Target Loads (3)

For calculating TLs the “inverse” of a dynamic modelis needed:

Scenario analysis: Al/Bc=Model (Dep,pars)

TL calculation: Dep=Model -1 (Al/Bc=1,pars)

Since Model -1 is not available, TL calculation requires the iterative use of Model:

What can happen when calculating TLFs?

(1) No time-dependent S and N processes (simplest case):

Target Load function

Critical load function Bc/Al=1,Cpool_0=0; Target year=2050Deposition reduction w indow

N deposition (eq/ha/yr)2.4002.2002.0001.8001.6001.4001.2001.000800600400200

S d

ep

osi

tion

(e

q/h

a/y

r)

1.500

1.400

1.300

1.200

1.100

1.000

900

800

700

600

500

400

300

200

100

CLmaxS

CLmaxN

Deposition in: 2010

What can happen when calculating TLFs?

(2) Time-dependent N immobilisation (Cpool >0): TLF becomes non-linear and may intersect with CLF.

Target Load function

Critical load function Bc/Al=1; Target year=2050Deposition reduction w indow

N deposition (eq/ha/yr)3.0002.5002.0001.5001.000500

S d

ep

osi

tion

(e

q/h

a/y

r)

1.500

1.400

1.300

1.200

1.100

1.000

900

800

700

600

500

400

300

200

100

CLmaxS

CLmaxN

Deposition in: 2010

Summary:

- TL calcs much more involved than CL calcs; however- TL output analogous to CL output (TlL functions) =>- Methods/tools used incorporating CLs into IAM can also be used for TLs (exceedance becomes non-achievement!)

State of play:

- Last call for data (<31-03-04) requested also TL calculations from NFCs (2030, 2050, 2100)- 8 (of 25) countries provided them- data are currently analysed- should be available during summer/fall