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Trends in Terrestrial Carbon Sinks Driven by Hydroclimatic Change since 1948: Data-Driven Analysis using FLUXNET Christopher Schwalm , Christopher Williams, Kevin Schaefer, Kusum Naithani, Jingfeng Xiao. Ameriflux Science Meeting & 3rd NACP All-Investigators Meeting 2011

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Trends in Terrestrial Carbon Sinks Driven by Hydroclimatic Change since 1948: Data-Driven Analysis using FLUXNETChristopher Schwalm, Christopher Williams, Kevin Schaefer, Kusum Naithani, Jingfeng Xiao

Ameriflux Science Meeting & 3rd NACP

All-Investigators Meeting 2011

January 31 – February 4, New Orleans, LA


Outline
Outline Change since 1948: Data-Driven Analysis using FLUXNET

  • We ask

    • What are the carbon consequences of hydrologic change?

  • We merge

    • Global monitoring network (FLUXNET)

    • LUH time-varying land cover (IPCC AR5)

    • NCEP/NCAR Reanalysis

  • We derive

    • Monthly time series (1948 – 2009)

    • 1° latitude/longitude resolution

    • Observationally-based estimates of carbon flux solely attributable to hydrologic change


Global monitoring network
Global monitoring network Change since 1948: Data-Driven Analysis using FLUXNET

FLUXNET: Network of regional networks

Eddy covariance method: temporally dense in situ CO2 exchange including gross primary production and ecosystem respiration

Ancillary data: soil moisture, temperature, latent heat flux, LAI, etc.


Mapping points to pixels

Carbon Flux Change since 1948: Data-Driven Analysis using FLUXNET

Evaporative Fraction

Mapping points to pixels

Extract relationship between hydrologic change and carbon flux

Aggregate FLUXNET sites by IGBP land cover class

Calculate sensitivity: change in carbon flux to a unit forcing in evaporative fraction (z-score)

Sensitivity: g C m-2 month-1σ-1

Map sensitivities to globe using

1) LUH [gridded land cover class]

2) NCEP/NCAR Reanalysis [gridded EF]

Schwalm et al. (2010) Global Change Biology


Spatial scaling luh land cover
Spatial scaling: LUH land cover Change since 1948: Data-Driven Analysis using FLUXNET

“Points to pixels”

IGBP maps

18 IGBP land cover classes by pixel

1948

+

FLUXNET sensitivities

Vegetated classes – observed

Non-vegetated classes – set to zero

62 annual snapshots of land cover from Land Use Harmonization (LUH)

Crosswalk: LUH → IGBP

=

Pixel sensitivity [weighted average]

2009

Units: g C m-2 month-1σ-1

http://luh.unh.edu/


Temporal scaling: NCEP reanalysis Change since 1948: Data-Driven Analysis using FLUXNET

Example – Europe in June 1998

NEP sensitivity

(g C m-2 mon-1σ-1 )

EF (σ)

δNEP (g C m-2 mon-1)


Global time series
Global time series Change since 1948: Data-Driven Analysis using FLUXNET

Sink (2000-2006) = +2.8 Canadell et al. (2007) PNAS


Global trends
Global trends Change since 1948: Data-Driven Analysis using FLUXNET

Trend line (p > 0.44)

Visually the same as zero reference line

Grey envelope is ±2σ


Continental trends nep

More uptake Change since 1948: Data-Driven Analysis using FLUXNET

Less uptake

Less uptake

Continental trends - δNEP

significant

not significant

More uptake


Continental trends p r
Continental trends – Change since 1948: Data-Driven Analysis using FLUXNETδP & δR


Cumulative trend
Cumulative trend Change since 1948: Data-Driven Analysis using FLUXNET

outgassing

uptake

TNEP [g C m-2 62yr-1]


Differential response case study
Differential response: Case study Change since 1948: Data-Driven Analysis using FLUXNET

Highest density of FLUXNET sites


Geography of hydrologic change
Geography of hydrologic change Change since 1948: Data-Driven Analysis using FLUXNET


Cru vs willmott precipitation
CRU vs. Willmott precipitation Change since 1948: Data-Driven Analysis using FLUXNET


Relating trend to background flux
Relating trend to background flux Change since 1948: Data-Driven Analysis using FLUXNET

FLUXNET + LUH + NCEP

δR

δP

Does the trend overpower the mean?

What spatial features are present?

δNEP

R

P

NEP

MODIS + CARBONTRACKER


Net effect on gross fluxes
Net effect on gross fluxes Change since 1948: Data-Driven Analysis using FLUXNET

|δP| > |δR| - color contrast

Median ratio 40% larger for |TP/P| than for |TR/R|

More clusters with |δP| > P

Fewer clusters with|δR| > R

Low productivity areas


Net effect on source sink
Net effect on source/sink Change since 1948: Data-Driven Analysis using FLUXNET

Blue: source to sink [4%]

Red: sink to source [20%]

Green: enhanced uptake [18%]

Yellow: enhanced outgassing [12%]


Summary
Summary Change since 1948: Data-Driven Analysis using FLUXNET

  • Observationally-based estimates of carbon cycling solely attributable to hydroclimatic variability

  • Range in del equals or exceeds terrestrial carbon sink magnitude or gross fluxes.

  • Hydroclimatic variability has acted to flip sources to sinks and vice versa (25%) over the 62-yr record → “key player”


Net effect on photosynthesis
Net effect on photosynthesis Change since 1948: Data-Driven Analysis using FLUXNET


Net effect on respiration
Net effect on respiration Change since 1948: Data-Driven Analysis using FLUXNET


Net effect on gross fluxes1
Net effect on gross fluxes Change since 1948: Data-Driven Analysis using FLUXNET

Less assimilation

Trend < 0

More assimilation

Trend > 0


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