1. GHG and SOC Modelling
HYDROMET, University College Cork.
Rashid Rafique; Xianli Xu; Matthias Peichl; Michael Mishurov; Ger Kiely
EPA National Workshop
Modelling Efforts for Greenhouse Gas Accounting in Irish Agriculture and Associated Land Use
November 24, 2010.

2. OUTLINE
1. Data
2. PaSim
3. DnDc
4. Empirical Scenario modelling for N2O
5. RothC

3. 1. DATA

4. Eddy Covariance Flux Sites
• Three sites with CO2 EC data since 2002
• Two grassland, one peatland
• Dripsey grassland with N20 EC since 2002
• 4th site for CO2 EC at Dripsey forest 2009

5. Chamber N20 Sites
8 chamber N2O sites in
Munster with weekly or
biweekly data for 2008/09.

6. Soil Carbon Sampling Sites
SoilC SoilH ForestC
67 sites (2006/07) 43 sites (2008/09) 38 sites (2006/07)

7. 2. PaSim

8. Modelling net ecosystem exchange of CO2 in intensively managed
humid-temperate grassland using the PaSim Model
PaSim 3.6 (v5) is a mechanistically
based ecosystem model which
simulates the:
carbon, nitrogen and water balances
of the
atmosphere-plant-soil system and
can be used to predict dry matter
production of fertilized and cut mixed
perennial meadows.
The model consists of the five sub-
models:
- Soil physics
- Soil biology
- Plant
- Animal
- Micro-climate

9. Time series - Comparison of PaSim model estimates to eddy-covariance measurements
taken from Lawton et al. (2006)

10. Annual CO2 exchange –
PaSim vs eddy-covariance measurements
Yr Measured Modelled
T C ha-1 yr-1 taken from Lawton et al. (2006)
2002 1.9 2.6
2003 2.7 2.6
2004 2.9 3.4

11. 3. DnDc

12. 12
DNDC : A process oriented computer simulation model
 DNDC components:
First component: soil climate, crop growth and decomposition
(predicts soil temperature, soil moisture, pH, redox potential)
Second component: nitrification, denitrification and fermentation
(predicts trace gases i.e. N2O, CH4, NH3 etc)
 DNDC Use: Cropping, Grazing, and forest systems.
Model validation (validation against experimental data)
Regional inventories (estimate GHG at national scales)
 Sensitivity of DNDC: Very sensitive to climate, soil, and crop inputs
 Results of DNDC: depends on the availability and quality of data.
It varies from good agreement to poor agreement with measured data.
Reproduces general trends and the annual fluxes but poor reproducibility
of instantaneous and daily fluxes

13. Measured N2O Flux = 11.5 kg N-N2O ha-1 yr-1. DnDc Modelled = 15.4 kg:
EFmeasure = 3.4%: EF modelled = 4.6%

14. 11o W 10o W 9o W 8o W 7o W 6o W 5o W
14
Study Sites
 Temperate climate with annual precipitation 54o N
of 1200 mm
 Daily temperature ranges from 5 oC in 53o N
winter to 15 oC in summer Pallaskenry
Solohead
Kilworth
Carrairg na bhFear
 Soil types were Grey brown Podzolic,
Donoughmore
52o N
Ballinhassig
Brown Podzolic and Gleys Clonakilty
 All sites are active pastures and most of
them are frequently grazed (LUha-1 1.0-3.0) 1. Ballinhassig
2. Clonakilty
3. Carriag nabhFear
 Total N application range from 121 kg N ha-
1 yr-1 to 446 kg N ha-1 yr-1
4. Donoughmore
5. Pallaskenry
6. Kilworth
7. Solohead1
8. Solohead2

15. 15
N2O Fluxes Time Series (Measured & Modeled)
BH
SH1
CK
Julian Days (2008 & 2009)

16. 16 Model validation (Measured & Modeled)
16
Statistical Verification
Modelled (kg N2O-N ha-1 yr-1)
14
2
R = 0.5083
12
Sites BE MAE RMSE rRMSE R2
10
BH -0.003 0.007 0.010 0.57 0.56
CK -0.032 0.021 0.034 0.67 0.45 8
D 0.016 0.026 0.041 0.90 0.38 6
CF -0.006 0.020 0.024 0.60 0.49 4
PK -0.003 0.020 0.017 0.59 0.44 2
KW -0.004 0.020 0.017 0.59 0.43
0
SH1 0.003 0.007 0.012 0.59 0.58 0 2 4 6 8 10 12 14
SH2 -0.0001 0.070 0.091 0.60 0.32 Measured (kg N2O-N ha-1 yr-1)
Overall -0.004 0.024 0.031 0.639 0.456
•Overall the average annual modelled annual
Annual flux 1.39 1.75 2.98 0.47 0.51
flux was about 20% higher than measured

17. N2O flux scenario under different management by
using DNDC
18
16
Current management
N2O flux (kg N2O-N ha-1 yr-1) 14 50% reduces N input and LU
Rough management
12
50% increased N input and LU
10
8
6
4
2
0
BH CK D CF PK KW SH1 SH2
Sites
Sites % decrease % increase
BH 15.18 9.45
• The % decrease is from current management to
CK 33.53 7.55 rough management ranged from 15.18 to 57.31
D 57.31 11.99
• The % increase is from current management to 50%
CF 22.11 9.145
increase N input which is ranged from 7.46 to 36.94
PK 19.73 9.40
KW 17.74 10.83
SH1 56.13 36.94
SH2 26.32 7.46
Over all 31.01 12.85
Further task: To work with DNDC and up scale N2O emission for Ireland

18. 4. Empirical Scenarios

19. Scenario analysis of future N2O emissions
• Two time frames: 2020 and 2050 (baseline year
2000)
• Input datasets:
– Common IPCC SRES scenarios: A1, A2, B1
– Climate predictions: C4I (http://www.c4i.ie/)
– Land use change: ATEAM (http://www.pik-
potsdam.de/ateam/)
– N fertilizer use based on that REPS farms
• Emission factors (EF):
– Default IPCC Tier 1 EF (fixed 1%)
– Climate- and crop-responsive EF (Flynn et al., 2005)
– Climate-sensitive EF (Flechard et al. 2007)

20. Scenario analysis: Main conclusions
• Significant drop in grassland area
is the major driver of N fertilizers
use decrease
Croplands + N2O
Year Fertilizers
• Crop lands become marginally grasslands emissions
more prominent both in terms of
land area and the amount of 2000 39 365 km2 408 kt N 0.5-39.0 kt N
N2O emissions
• Climate change would generally 2020 −16 to −28% −40 to −48% −5 to −52%
increase emissions, however, its
contribution is heavily
2050 −31 to −38% −50 to −55% −13 to −57%
dependent on choice of EF
methodology

21. 5. RothC

22. Modelling the change in soil organic carbon (SOC)
of grassland in response to climate change:
effects of measured versus modelled carbon pools
for initializing the RothC model

23. RothC model initialization issue
The objective of this study was:
to test whether the measured carbon
fractions with the procedure of Zimmermann et
al. (2007) are well related with the modelled
pools as required by RothC;
to determine the effects of different
initializations of the RothC model with
measured or modelled carbon pools on the
outputs of SOC;
to examine the effects of climate change on
SOC in the temperate grasslands of Ireland.

24. Converting measured fractions to carbon pools
Zimmermann et al. (2007)
RothC
Plant inputs
DPM=Decomposable
Plant material
RPM = Resistant Plant
DPM+ Material
DPM
RPM Splitting ratio DPM/RPM
POM DOC HUM = Humified Organic
calculated by
equilibrium scenario Material
RPM BIO = Microbial Biomass
IOM = Inert Organic
Matter
HUM+
s+c – BIO Splitting ratio BIO/HUM HUM
DPM Zimmermann (2007)
S+A calculated by
rSOC
equilibrium scenario s+c = silt +clay
Physically protected
BIO
RPM S+A = Sand and stable
aggregates
IOM
POM = Particulate OM
rSOC IOM
RPM
DOC = Dissolved OC
Chemically protected Fractions Pools rSOC = Resistant SOC

25. Climate change from 1961-2000 to 2021-2060 from C4I
1961-2000 A1B A2 B1 1961-2000 A1B A2 B1
200 16
180 14
Precipitation (mm)
Temperature (°C)
160 12
140 10
120 8
100 6
80 4
1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12
Month Month
In future:
wetter winters and drier summers
higher temperatures

26. Measured and modelled carbon pools
The measured and modeled
Modelled DPM (t C/ha)
Modelled RPM (t C/ha)
1.5 15 values for BIO and HUM
1:1 line significantly correlated with
1:1 line
1.0 10 SolA each other, while not for DPM
SolB
and RPM
Pall
0.5 5 Drip
Ball For Pall, SolA and SolB, good
surface drainage due to the
0.0 0
sloping lands and man-made
0.0 0.5 1.0 1.5 0 5 10 15 drainage channels which likely
Measured DPM (t C/ha) Measured RPM (t C/ha) accelerated the decomposition
Modelled HUM (t C/ha) of the RPM pool
Modelled BIO (t C/ha)
1.5 60 For Ball and Drip, poor drainage
(underlying iron at Drip and
1.0 40 samples taken in flat areas at
Ball) is likely to have slowed the
decomposition of the RPM pool
0.5 20
0.0 0
0.0 0.5 1.0 1.5 0 20 40 60
Measured BIO (t C/ha) Measured HUM (t C/ha)

27. 25 Ball A1B_Me A1B_Mo Carr
45
A2_Me A2_Mo
24 B1_Me B1_Mo RothC predicted SOC
Total SOC (t/ha)
44
23 changes 2021 to 2060
43
22
21
1 4 7 10 13 16 19 22 25 28 31 34 37 40
42
1 4 7 10 13 16 19 22 25 28 31 34 37 40
For the sites of Carr, Clon, and Kilw,
Year
Clon Drip
the projected SOC change trends
39 35
from the initialization of the
34
38
33 measured pools were similar to
32 that when RothC was initialized
31
37
30
with the modelled pools
29
36 28
1 4 7 10 13 16 19 22 25 28 31 34 37 40 1 4 7 10 13 16 19 22 25 28 31 34 37 40
For the sites of Ball and Drip, the
35 Kilw 27 Pall projected SOC change trends with
initialization of the measured pools,
26
34 rapidly decreased firstly and then
25
slightly increased
33
24
32
1 4 7 10 13 16 19 22 25 28 31 34 37 40
23
1 4 7 10 13 16 19 22 25 28 31 34 37 40
For the sites of Pall, SolA and SolB,
the projected SOC change trends
Sol SolB
72
A 41 with the initialization of the
71 40 measured pools rapidly increased
70
69
39
firstly and then decreased relatively
68
38
slowly
67 37
66 36
1 4 7 10 13 16 19 22 25 28 31 34 37 40 1 4 7 10 13 16 19 22 25 28 31 34 37 40

28. RothC Summary
 The Zimmermann method has great potential, the measured carbon pools
more reasonably reflect the real environmental conditions (i.e. drainage)
than the modelled pools
 The difference in the predicted SOC outputs among the sites depends on
the balance between the measured and modelled RPM pools
 In response to a future of rising temperature and expected drier summers
and wetter winters, RothC predicts a decrease in the SOC of Irish
temperate grasslands

29. CONCLUSIONS
• PaSim shows much promise
• DnDc is reasonable over the annual cycle by comparison with sub-
daily time scales
• Empirical Scenario Analysis show large reductions to be expected
in N2O for future climate and land use changes
• RothC predicts lower SOC under climate change
• Now that we have good data, we should be able to make significant
progress in modelling

30. Thank You

31. 30
25 DPM
SOC (t C/ha) RPM
20
BIO
15
10
HUM RPM controls Total SOC trend
IOM
5 Total
0
1 4 7 10 13 16 19 22 25 28 31 34 37 40
Year
 Under the conditions that
11
10 Measured
facilitating decomposition
9 Modeled
RPM (t C/ha)
8
7 •If Measured >Modelled RPM
6
The measured rapidly decrease
5
4 until another new equilibrium
3
0 3 6 9 12 15 18 21 24 27 30 33 36 39
Year •If Modelled > Measured RPM
3.5
The measured rapidly increase
3 until another new equilibrium
RPM (t C/ha)
2.5
2
1.5 Measured
1 Modeled
0.5
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Year