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Martha P. Butler The Pennsylvania State University ChEAS Meeting June 29 – July 2, 2003

Explore ecosystem responses to Spring 1998 climate anomaly using FLUXNET data, CO2 signals, and temperature analyses to detect regional impacts and land carbon uptake.

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Martha P. Butler The Pennsylvania State University ChEAS Meeting June 29 – July 2, 2003

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  1. Spatial Coherence of NEE Response of Different Ecosystems to the Same Climate Anomaly(A Spring 1998 Case Study) Martha P. Butler The Pennsylvania State University ChEAS Meeting June 29 – July 2, 2003

  2. Premise • Different ecosystems, separated in space, exposed to the same climate anomaly, may have similar responses. • If the climate anomaly includes a large area, the shared ecosystem response may be large enough to be detected globally. • Can flux tower measurements be combined to represent regional responses?

  3. Test • Pick a climate anomaly that might be expected to have a widespread response. [Spring 1998] • Locate FLUXNET sites within the anomaly area with data for Spring 1997 and Spring 1998. • Identify and quantify the common response. • MAM mean temperature, cumulative MAM NEE • Look for evidence in local and global CO2 signals.

  4. Why Spring? Why 1998? • In Spring there are detectable phenological changes, especially in deciduous forests. • Onset of photosynthesis, soil thaw • Change in relationship of latent heat flux to sensible heat flux • Spring 1998 was one of the warmest on record for parts of the Northern America. • An El Niño winter…

  5. Map shows the location of grid boxes with station data for January-July 1998 that contributed to our global land analysis. The size and color of the dots indicate how much warmer or colder January-July 1998 was compared to January-July 1997.

  6. Surface Temperature Anomalies in °C (1961-1990 base period) December 1997- February 1998 March 1998 – May 1998 Bell et al., BAMS, Vol.80, No. 5, 1999

  7. A Closer View Of the US Record May 1998 Climate Variations Bulletin National Climatic Data Center, NOAA

  8. Criteria for Choosing Sites • Availability of NEE Data for Spring 1997 and Spring 1998 • Gap-Filled FLUXNET Data Sets • Mirror Sites to PI-Maintained Data • Published Literature • Availability of Good Quality CO2 Mixing Ratio Time Series • Inside/Outside Boundaries of Warm Anomaly • Vegetation Type

  9. Sites Considered…

  10. Comparison of Spring 1998 to Spring 1997 Order of Magnitude of increase in carbon uptake: 50g C m-2 spring-1 (managed) (outside of anomaly) *Old Aspen data from Black et al., 2000; Mean Temperatures are for April-May; cumulative NEE is estimated from Figure 1 **CO2 Flux reported for Howland Forest (not NEE) ***All other data from FLUXNET monthly summary, gap-filled by look-up table method, ustar-screened, from http://daac.ornl.gov/FLUXNET/

  11. Timing of Spring Onset The “cross-over” of latent and sensible heat fluxes in these deciduous and mixed forests occurred earlier in 1998 than in 1997. Data are 15 day bin averages of mean daily fluxes. Source: FLUXNET gap-filled daily data

  12. Quality/Availability of CO2 Mixing Ratio Measurements

  13. Evidence in the Local CO2 Record Earlier spring decrease in mean daytime CO2 mixing ratios in 1998. An early spring is not necessarily a guarantee of a productive summer growing season. Data are 15-day bin averages for hours 10-14 LST. Howland Forest data courtesy of D. Hollinger. All other data from PI-maintained FLUXNET mirror sites.

  14. Questions • If much of North America is affected, can this signal be seen in the global CO2 measurement network? • Or… • What does the global measurement network show? • What is the magnitude of the land response that could account for the global observations? • First cut, simple approach, with many assumptions:

  15. An Order of Magnitude Scaling Exercise • Consider two sites in the CO2 global measurement network, at roughly 53N. • Assume a mean westerly wind, U = 10 ms-1 • Assume that any change in CO2 between the two sites is due to land interaction in North America (land traverse of d = 5 x 106 m). • Assume any change in CO2 is mixed through the depth of the troposphere, • h = 104 m.

  16. Scaling Exercise (continued)… • Find the mean difference in CO2 mixing ratio between SHM and MHD for Spring 1997 (March, April, May). • Find the net land flux, E – D (Emissions – Deposition), that would account for this CO2 difference using dC/dt = E/h – D/h, where • ΔC = [CO2] at MHD – [CO2] at SHM • Δt = d/U • Repeat for 1998. • Compare the net land flux differences for 1997 and 1998. • Compare this result to 50g C m-2 more terrestrial uptake for Spring 1998 that seems plausible from the flux tower results. • Ready? Let’s do it…. • ΔC for 1997 is -1.52 ppm • ΔC for 1998 is -2.05 ppm

  17. Scaling Exercise Results • For 1997: (E – D) = (h U ΔC)/d • (104 m)(10 ms-1)(-1.52 ppm) / (5 x 106 m) = -0.030 ppm ms-1 • Convert to gC m-2 day-1 (multiply by 35) = -1.06 gC m-2 day-1 • Multiply by 100 days = -100 gC m-2 spring-1 • For 1998: • (104 m)(10 ms-1)(-2.05 ppm) / (5 x 106 m) = -0.041 ppm ms-1 • -1.44 gC m-2 day-1 • -140 gC m-2 spring-1 • 40 gC m-2 more uptake in Spring 1998 compared to Spring 1997. • Challenges? • Implications?

  18. Next Steps • What about Europe? • Try another anomaly (more recent, with more operational flux towers) • Apply more rigorous geostatistical methods. • Make the scaling exercise more rigorous • Use the flux towers measurements (including CO2 data) to extend the global measurement network to include more land sites.

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