1) Current greenhouse gas emission reporting methods provide simple estimates that may not accurately reflect actual emissions and do not help guide mitigation. 2) Process-based models can provide more detailed and accurate estimates of emissions by taking into account factors like soil type, temperature, fertilizer use and crop growth, which inter-annual reporting methods do not. 3) Improving emission estimates through measurement data, refined models and reporting approaches can help develop agricultural systems that reduce environmental impacts from greenhouse gas emissions.

1. Reconciling greenhouse gas
emissions from measurements and
modelling in the land use sector
Bob Rees, Kairsty Topp
ICARB workshop, 5 February 2013

2. Reporting metrics
• UK greenhouse gas emissions reported using
internationally agreed protocols (IPCC)
• Provide simple rule based accounting system
• Underpin C footprinting tools
• Unlikely to reflect actual emissions
• Unhelpful in guiding mitigation
2

3. IPCC approach to GHG inventory
IPCC 2006
3

4. Scottish GHG emissions
NAEI 2012 4

5. Inter-annual variation of N2O
emissions
5
Smith and Dobbie 2002

6. Historic datasets
70
60
50
Fr e q ue nc y
40
30
20
10
0
- 0 .0 1 0 .0 0 0 .0 1 0 .0 2 0 .0 3 0 .0 4 0 .0 5 0 .0 6
Emis s io n Fa c t o r ( %)
An analysis of 237 individual historic UK observations. Buckingham et al 2012
6

7. Climatic controls of nitrous oxide
emissions
Scottish
summers
Flechard et al, Agriculture, Ecosystems and Environment 121 (2007) 135–152
7
7

8. Emissions calculations
Annual N2O emission (kg N ha-1)
 IPCC default EF
assumes N2O
emissions from soil are
supply-related
 But at least some 0 100 200 300 400
arable soil emissions
Annual N2O emission (kg N ha-1)
N application rate (kg ha-1)
must be N-balance-
related … because
they will occur after the
crop has taken up
some fertiliser N
0 100 200 300 400
N application rate (kg ha-1) 8
Thorman et al, 2012

9. Inventory comparison with Model
Is the NAEI emission inventory overestimating UK N2O emissions?
250
200
150
kt N2O/y
100
50
0
1990 1995 2000 2005 2010
NAME 5th 95th Inventory
A. Manning
9

10. DEFRA: improving N2O inventory
UKIPCC Tier 1 N2Dynamics Model
Specific Tier 3 N Dynamics Model
Inventory
1% fn{N
10% type, Soil temp}
NDevelopment
2 O EFDeposited NH3 fVolatilisation
programme will
Emissions Deposition
N Type Soil Temperature
improve
structure and 2.5% fn{Soil
28%
30% type}
Internationa
fLeached
l Reporting refine EFLeachate Emissions Model
N Leached
Emissions Soil Type
N Type
Factors via plot fn{N type,
0.8%
1.25% SMC, pH}
National N/Manure
to field scale EFDirect
Reporting Applied
measurementsSoil Moisture Content Soil pH
GHG platform programme
10

11. Process based modelling
Soil Characteristics Crop Parameters
Climatic Drivers Farming Practices
Crop Growth/ Climate Soil
Development Physics
Soil C,N
Biochemistry
Crop Production Trace Gas Emissions
Soil C, N Dynamics N leaching
11
DNDC

12. Validation
Easter Bush 12 12

13. Daily nitrous oxide fluxes in the arable phase
of a rotation
800
g N2O-N ha-1 d-1
Fertiliser
600
applications
400
200
0
01-Jan 01-Mar 30-Apr 29-Jun 28-Aug 27-Oct 26-Dec
DNDC 9.2 Rees et al, 2008
13

14. Regional modelling
• Homogeneous
Mapping Spatial Unit
DNDC
(HMSU) etc.
– Soil type
– Slope
– Land cover
– Admin boundaries
– agronomic practices
and climate are similar
14

15. Conclusions
• Current inventory reporting of agricultural GHG
emissions provide a crude estimate of actual
emissions
• Improved reporting will help improve the accuracy
of emissions and help to deliver mitigation
• Revised emission factors in improved modelling will
provide opportunities for the development of
farming systems with reduced environmental
impact
15
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