Dynamic Modelling and its Use
in Integrated Assessment Models
Maximilian Posch
Coordination Center for Effects
(ICP M&M&, WGE)
RIVM/MNP
Bilthoven, 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) of
areas where critical loads were, are and will be exceeded
under different deposition scenarios
- This cannot be done with Critical Loads!
Target Loads are one way to link dynamic model results
to IAM.
Delay in Damage and Recovery:
Deposition
Delayed
chemical response
Further delayed
biological response
What causes these delay times?
Finite buffers in the soil (irrelevant for steady state)
1. Cation exchange
Characterised 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 ecosystem
status (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
Protocol year
DM target year 1
1960
1980
2000
2020
DM implementation year
2040
2060
DM target year 2
Target Loads (3)
For calculating TLs the “inverse” of a dynamic model
is 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:
Select (future) Dep
Run Model
Al/Bc in target year = 1?
Yes: TL=Dep; No:
What can happen when calculating TLFs?
(1) No time-dependent S and N processes (simplest case):
Target Load function
Deposition in: 2010
1.500
CLmaxS
1.400
1.300
1.200
1.100
1.000
900
800
700
600
500
400
300
200
100
CLmaxN
200
400
600
800
1.000 1.200 1.400 1.600 1.800 2.000 2.200 2.400
N deposition (eq/ha/yr)
Critical load function
Deposition reduction w indow
Bc/Al=1,Cpool_0=0; Target year=2050
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
Deposition in: 2010
1.500
CLmaxS
1.400
1.300
1.200
1.100
1.000
900
800
700
600
500
400
300
200
100
CLmaxN
500
1.000
1.500
2.000
2.500
N deposition (eq/ha/yr)
Critical load function
Deposition reduction w indow
Bc/Al=1; Target year=2050
3.000
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