trade-offs between sequestration and bioenergy benefits nicolas vuichard (1,2) philippe ciais (2)...
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Trade-offs between sequestration and bioenergy benefits
Nicolas VUICHARD (1,2) Philippe CIAIS (2)
Luca BELELLI (3) Riccardo VALENTINI (3)
(1) CIRED – Nogent (France)(2) LSCE/IPSL – Saclay (France)
(3) University of Tuscia – Viterbo (Italy)
Growing biofuels over abandoned croplands
in the former USSR
• Abandoned cultivated lands are suitable candidates for bioenergy production (Field, 2008)► Do not compete with food security► Dot not induce a carbon debt
• Bioenergy competes with soil C sequestration but has a higher environmental impact
• Is there an optimal onset time to start biofuel cultivation, given future climate change and management practices?
The end of the USSR resulted into one of the largest crop
abandonment of the 20th century
- 20 Mha
Hurtt et al., 2006
20 Mha
Soil carbon changes are impacted by
CropsRecovering grassland
Natural grassland
Soi
l car
bon
+ Climate + Climate
++ Management
+ Climate
++ Land-use legacy
1950’s 1990’s
A potential of 0.5 GtC could be sequestered
into the abandonned 20 Mha of croplands
New soil C data from abandonned crop fields in Russia
Goals
• Carbon benefit of sequestration by natural steppe recovery
• Carbon benefit of biofuel due to both:- biofuel can also sequester below ground C- biofuel harvest substitutes to Fossil Fuel
• Compare recovery vs. biofuel option
-> Use a spatially explicit process-basedmodel to address these questions
The ORCHIDEE global carbon-water-energy model
ORCHIDEESECHIBA
energy & water cyclephotosynthesis
t = 1 hour
LPJspatial
distributionof vegetation(competition, fire,…)t = 1 year
STOMATEvegetation & soil carbon
cycle(phénologie, allocation,
…)
t = 1 day
NPP, biomass,litterfall
vegetation types
LAI,roughness,
albedo
soil water,surface temperature,
GPP
rain, température, humidity,incoming radiation, wind, CO2
meteorological forcing
sensible & latent heat fluxes, CO2 flux, net
radiation
output variables
prescribed vegetation
vegetation types
Including crops in ORCHIDEE
Same Gridded climate and soil
data
STICS agronomic Model
Library of ≠ crop varieties
LUE growth
Biomass allocation and yield
Water and Nitrogen demand
No soil C balancescale : field , months
ORCHIDEE global modelGeneric ecosystem C dynamics
with land-use disturbances
scale : local => regional => global
1 year => 1000 years
Brisson et al. (2002)
LAIRoot profileIrrigation needs
Daily data assimilation of crop parameters into ORCHIDEE
• Input (spatially explicit) land-use statistics FAO
Including land-use change & land management
• Input N-fertilizer addition statistics USDA
• Simple agricultural parameterizationHarvest -> grains + straw exported
Tillage -> Mean Residence Time of soil C pools faster by 30%
time
1951 1993 Recovery period 2000
Orchidee-Stics Orchidee
Cultivation period
on arable land of former USSR
Croplands100% instant. aband.
If croplands all maintained after 1993If croplands all abandoned in 1993Realistic abandonment scenario
g
C m
-2 y
r-1
Sink regional mean
Net Carbon Balance changes
agriculture
1951 1993
recovering grassland
2000
Orchidee-Stics Orchidee
Sink spatial patterns
Regional C gain from 1993 to 2000 373 gC per m2
Some grid points in the south are net sources, because NPP of steppes is
lower than soil carbon input from former crop fields
-> we really need spatially explicit modelling
Towards realistic estimates
Map of the C storage from 1993 to 2000
Abandoned cropland area from 1993 to 2000
C gain from 1993 to 2000 per m2
64 TgC in 8 years over 17 Mha
Sensitivity tests
• No fertilization during cultivation period
=> +37%• No tillage during cultivation period (no impact
on soil decomposition)
=> -25%• 10% of straw remained on plot
=> -15%
Modelling Biofuel on the steppe
• Ethanol production from natural grassland biomass as in Tilman et al. (2006)►1 gC substitutes 0.42 gC
• Scenario: an abrupt switch to biofuels in 1990
• Compare scenario with sequestration by calculating the crossing time tcross
• tcross = time at wich biofuels deliver more C benefits than sequestration
Biofuel production vs steppe recovery sequestration
Soil C sequestration in natural steppe
Total Bioenergy production
Soil C sequestered with Bioenergy production
tcross
Timing of bioenergy implementation• If we wait 60-years after abandonment to
install biofuels ?
• Trajectories change... but same tcross
Soil C sequestration
Bioenergy production
Soil C released with bioenergy production
tcross
Sensitivity to C initial stocks
• Condition: MRT must remain constant over time• This condition could be challenged if
Warming accelerates decompositionTillage must be increased for cultivating biofuels
Tilling t0=just after abandonment
Tilling t0=60 years after abandonment
Never tilled
tcross tcross tcross
Conclusions
• Biofuel production looks suitable on abandoned croplands of former USSR
• Energy = 0.23 EJ per year (0.05% of world demand)
• Net Carbon balance of biofuelssink of 0.56 Gt C over 60 years- Carbon storage in biofuel soils = 0.08 GtC - Fossil carbon substituted = 0.48 Gt C
• Net Carbon Storage if steppe recoverysink of 0.3 Gt C over 60 years
Crossing date = 11 years, at which biofuels have a better carbon balance than steppe recovery
Crossing date is relatively insensitive to timing of implementation under some conditions (no soil warming)
Quick benefits