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
15