Post on 30-Jan-2016
description
Changes in the seasonal activity of temperate and boreal vegetation
The critical role of Autumn temperatures.
Shilong Piao, Philippe Ciais,
Pierre Friedlingstein, Philippe Peylin, Nicolas Viovy and
Peter Rayner
LSCE, CEA-CNRS-UVSQGif sur Yvette, France
Carbon Fusion Meeting 9-11 May 2006
As temperature is rising, the length of growing season usually increases.
How will the net
Carbon Uptake Period
respond to the
warming ?
Jan DecJul Aug
earlier spring
delayed fall
Background
Global biospheric model ORCHIDEE
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
ORCHIDEE model simulations
1. Spin up (1000 y) using 1901 climate data, and 1850 CO2 concentration
2. Simulate from 1850 to 1900 using 1901-1910 climate data, and corresponding every year CO2 concentration.
3. Simulate from 1901 to 2002, using corresponding every year climate data and CO2 concentration. Save every day C flux from 1980 to 2002.
65
70
75
80
85
1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 2001
Year
NPP, RH (Pg C)
-6
-3
0
3
6
NEP (Pg C)
NPP
RHNEP
Comparison of spring (AM) LAI
0
1
2
3
4
5
6
- 55 - 45 - 35 - 25 - 15 - 5 5 15 25 35 45 55 65 75
GIMMSPath finderORCHIDEE
Latitude (degree)
Comparison of autumn (SO) LAI
0
1
2
3
4
5
6
- 55 - 45 - 35 - 25 - 15 - 5 5 15 25 35 45 55 65 75
GIMMSPath finderORCHIDEE
Latitude (degree)
Interannual Variability in LAI
Spring
SDORCHIDEE = 0.04
SDGIMMS = 0.06
SDPAL = 0.19
Satellite sensor change
Autumn
SDORCHIDEE = 0.02
SDGIMMS = 0.07
SDPAL = 0.13
Define growing season and carbon uptake periods
A BC
D
A = growing season startB = growing season endAB = growing season length (GSL)
C = net carbon uptake startD = net carbon uptake endCD = Carbon Uptake Period (CUP)
1001 ×−+= ( )]AI t( )]/[LAI t L)[ (LAI t( )tLAIratio
Growing SeasonFrom rate of change of LAI
CUP
GSL
Carbon UptakeFrom NEP zero-crossing dates
Mapping the growing season and carbon uptake timing
Onset date increases with increasing latitude
CUP start occurs later than GS start (because of spring respiration)
Shortest GSL = Central Siberia near the Arctic coast (4 months).
Shortest CUP = Northern Eurasian forests and water limited steppes - also show the shortest GS length.
The distribution of End date in autumn is less uniform than in spring, (reflects vegetation type, as well as water / temperature limitations on plant growth).
Growing season(phenology)
Carbon Uptake
Start (day)
End (day)
Duration (days)
Derived from ORCHIDEE simulation
Trends GSL and CUP during 1980-2002
dGSLstart/dt = 0.16 days/yr
dCUPstart/dt = 0.19 days/yr
Same response of CUPstart and GSLstart to warming trend
RGSLstart-temp = -0.91 P<0.001
RCUPstart-temp = -0.62 P=0.002
dGSLend/dt = 0.14 days/yr
dCUPend/dt = -0.07 days/yr
Opposite response of CUPend and GSLend to warming trend !
RGSLend-temp = 0.71 P<0.001
RCUPend-temp = -0.51 P=0.01ORCHIDEE > 25°N
Spring
Autumn
Mapping the trends
More than 70% of the study region exhibits an advancing trend in the GSL start, especially in Eurasia.
In North America, large regions show delayed trends in the CUP start
GSL length : Trends to increasing GSL over high latitude regions, usually as a result of earlier beginning of growing season in Eurasia and later end of growing season in North America
CUP length : North America shows a trend to shorter CUP length, Eurasia has the opposite behaviour
GSL: most of northern North America shows a trend towards later GSL end, BUT there is a trend to earlier GSL end in temperate Western Eurasia (Europe).
CUP: 70% of the study region display a trend towards an earlier CUP end.
Growing seasonTrends
Carbon Uptake Trends
Beginning
End
Length
Derived from ORCHIDEE
(1) Period from 1980-2002; (2) Period from 1982-1998; (3) Period from 1988-2000
Comparison with satellite observation
Region Change in GSL start (days / year)
>0 = earlier ; <0 = later
Change in CUP
(days / year)ORCHIDEE(1) Zhou et al.(2)
Smith et al. (3)
North America
+0.04 -0.4 -0.08 0.12
Eurasia -0.32 -0.3 -0.39 -0.39
Region Change in GSL (days / year)
>0 = earlier ; <0 = later
Change in CUP
(days / year)ORCHIDEE(1) Zhou et al.(2)
Smith et al. (3)
North America
0.27 0.27 0.22 -0.11
Eurasia 0.11 0.21 -0.31 -0.07
Spring
Autumn
Atmosphere CO2 measurements
Although Keeling et al. (1996) found that there were no significant long-term changes in the upward zero crossing time at site Mauna Loa from mid-1970s to 1994, pronounced advancement at a rate of 0.77 days yr-1 (R=-0.65, P=0.001) is observed in the period of 1980-2002.
Temperature vs. Carbon Uptake Period
Spring
RBRW = -0.85, P<0.001
RMLO= -0.40, P=0.056
Autumn
RBRW = -0.60, P=0.003
RMLO= -0.59, P=0.005 (excluding 1992, 1993)
Differential response of gross C Fluxes to the warming trend in Northern Hemisphere (>25°N)
Spring: Warm temperatures accelerate growth more than soil decomposition. The annual relationship of NEP to temperature is positive=> Warming enhances carbon uptake
Autumn: Warm autumn accelerate growth less than soil decomposition. The annual relationship of flux to temperature is negative.=> Warming reduces carbon uptake
Derived from ORCHIDEE
Derived from ORCHIDEE
Autumn (SON) temperature vs. C Flux
Conclusion
Most of the study region exhibited extending of GSL, usually as a result of earlier vegetation green-up in Eurasia and later vegetation senescence in North America, which strongly supports a lengthening of growing season and greening trend at northern hemispheric observed in the past two decades.
Due to parallel stimulating soil carbon decomposition, increase in GSL does not necessarily lead to increase in CUP and eventually result in higher C net uptake.
Autumn warming does not benefit terrestrial net C uptake through postponing vegetation growing season end in the northern mid and high latitudes.
Relevance to IGCO
• Need for in situ phenological data• Need of long flux time series to confirm processe• Need for snow cover / frozen status of soil data• Long term satellite biophysical products (large
differences between sensors & data processing)• New CO2 column satellite obseravtions may allow
an unprecedented quantification of the spatial distribution in the CO2 seasonal cycle -> regional trends detection
• Integration of surface with atmospheric information
Thank you!