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Ameriflux Science Meeting & 3rd NACP All-Investigators Meeting 2011

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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Ameriflux Science Meeting & 3rd NACP All-Investigators Meeting 2011

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  1. 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

  2. Outline • 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

  3. Global monitoring network 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.

  4. Carbon Flux 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

  5. Spatial scaling: LUH land cover “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/

  6. Temporal scaling: NCEP reanalysis Example – Europe in June 1998 NEP sensitivity (g C m-2 mon-1σ-1 ) EF (σ) δNEP (g C m-2 mon-1)

  7. Global time series Sink (2000-2006) = +2.8 Canadell et al. (2007) PNAS

  8. Global trends Trend line (p > 0.44) Visually the same as zero reference line Grey envelope is ±2σ

  9. More uptake Less uptake Less uptake Continental trends - δNEP significant not significant More uptake

  10. Continental trends – δP & δR

  11. Cumulative trend outgassing uptake TNEP [g C m-2 62yr-1]

  12. Differential response: Case study Highest density of FLUXNET sites

  13. Geography of hydrologic change

  14. CRU vs. Willmott precipitation

  15. Relating trend to background flux FLUXNET + LUH + NCEP δR δP Does the trend overpower the mean? What spatial features are present? δNEP R P NEP MODIS + CARBONTRACKER

  16. Net effect on gross fluxes |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

  17. Net effect on source/sink Blue: source to sink [4%] Red: sink to source [20%] Green: enhanced uptake [18%] Yellow: enhanced outgassing [12%]

  18. Summary • 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”

  19. Net effect on photosynthesis

  20. Net effect on respiration

  21. Net effect on gross fluxes Less assimilation Trend < 0 More assimilation Trend > 0

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