Spatial and temporal dynamics of the terrestrial carbon cycle [Elektronische Ressource] : assimilation of two decades of optical satellite data into a process-based global vegetation model / Birgit Schröder

Birgit Eva Schröder

Sujets

• Biologie

Informations

• Publié par: universitat_potsdam
• Publié le: 01 janvier 2007
• Nombre de lectures: 16
• Langue: English
• Poids de l'ouvrage: 10 Mo

Extrait

Spatial and temporal dynamics of
the terrestrial carbon cycle

Assimilation of two decades of optical satellite data
into a process-based global vegetation model







Birgit Schröder

















Institut für Geoökologie,
Universität Potsdam
und
Potsdam Institut für
Klimafolgenforschung e.V.













































Elektronisch veröffentlicht auf dem
Publikationsserver der Universität Potsdam:
http://opus.kobv.de/ubp/volltexte/2008/1759/
urn:nbn:de:kobv:517-opus-17596
[http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17596]

Spatial and temporal dynamics of the
terrestrial carbon cycle

Assimilation of two decades of optical satellite data
into a process-based global vegetation model



Birgit Schröder







Dissertation
zur Erlangung des akademischen Grades
“doctor rerum naturalium” (Dr. rer. nat.)
in der Wissenschaftsdisziplin “Geoökologie”

eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakultät
der Universität Potsdam


Potsdam, den 8. Mai 2007





Institut für Geoökologie
und
Potsdam Institut für Klimafolgenforschung e.V.








ACKNOWLEDGEMENTS



My principal advisor, Prof. Dr. Wolfgang Lucht, is gratefully acknowledged for his advice and
support. I highly benefited from many fruitful discussions and support in all kinds of scientific
questions. Moreover, I greatly appreciate his confidence in me and his patience and
encouragement during my doubtful phases and during the childbearing period.
I am very grateful to Prof. Dr. Wolfgang Cramer who gave me the opportunity to work at PIK
and to participate at a summer school in the Netherlands as well as at LPJ meetings, and who
always had an open ear to scientific and personal problems.
I also gratefully acknowledge Ranga Myneni and Dong Huang from the University of
Maryland, who provided me with the latest updates of the global fPAR datasets immediately
after release, as well as Compton C. Tucker from NASA Goddard Space Flight Center who
helped me to understand and define the differences of various fPAR datasets.
Many thanks go to Sibyll Schaphoff who supported me in all kind of programming issues with
great patience, which was often necessary.
I’d also like to thank Dieter Gerten who introduced me to statistical issues and for his valuable
comments.
Kirsten Thonicke is gratefully acknowledged for helpful hints concerning the fire module in
LPJ, programming issues, and childbearing affairs.
Thanks go also to Tim Erbrecht who became my “contact person” for remote sensing and
biomass issues and for providing me with interesting music and hints for concerts going on in
Berlin.
This manuscript benefited from critical readings and by Wolfgang Lucht, Dieter Gerten,
Claudia Kubatzki, Elfrun Lehmann, and Tim Erbrecht.
I really appreciated the discussions, support and the fun I had with the members of the LPJ
consortium, (if they not have already been mentioned before): Stephen Sitch, Alberte Bondeau,
Tanja Rixecker, Christoph Müller, Sönke Zaehle, Pascalle Smith, Markus Reichstein,
Herrmann Lotze-Campen, Thomas Hickler, Wolfgang Knorr.
The German Climate Research Programme DEKLIM under the Ministry for Education and
Research (BMBF) funded this work as part of the project ‘Climate, Vegetation and Carbon’
(CVECA).
Last, but not least, I’d like to thank Gerhard Kaulard for his support and encouragement during
the difficult phase of pregnancy.
Finally, I’d like to dedicate this dissertation to my parents. I am highly indebted to them as they
spent a lot of time taking care for me and my little son during the last phase of this PhD thesis
and without their emotional, financial and temporal support this thesis would have never been
completed.
Abstract III




ABSTRACT


Current understanding of the factors that determine the magnitude and temporal variations of
global terrestrial uptake and release and which regions contribute most to these patterns is still
incomplete. Several modelling approaches have provided estimations of the spatio-temporal
patterns of net ecosystem production, but there is still a need for an improved and more realistic
global carbon cycle model with good resolution that does not only simulate potential vegetation
but also allows quantification of regional carbon storage and fluxes.
This PhD thesis presents the spatio-temporal distribution of terrestrial carbon fluxes for the
time period of 1982 to 2002 simulated by a combination of the process-based dynamic global
vegetation model LPJ (Sitch et al. 2003) and a 21-year time series of global AVHRR-fPAR
data (fPAR – fraction of photosynthetically active radiation), provided by Ranga Myneni of
Boston University at 0.5° resolution. Assimilation of the satellite data into the model allows
improved simulations of carbon fluxes on global as well as on regional scales.
Assimilation of the fPAR data was implemented as a two-step process: after a spin-up of the
potential vegetation to determine a base-line vegetation composition satellite-observed fPAR
values were ingested. The fPAR value of each grid-cell was decomposed into fractions
corresponding to the vegetation present at each location, where winter values were used to
determine the evergreen versus deciduous fractions. In agricultural areas the model-predicted
vegetation was replaced by grass; the satellite-observed fPAR provided the seasonality of
planting and harvesting as well as the temporal trajectory of agricultural vegetation growth.
As it is based on observed data and includes agricultural regions, the model combined with
satellite data produces more realistic carbon fluxes of net primary production (NPP), soil
respiration (Rh), carbon released by fire and the net land-atmosphere flux than the potential
vegetation model. It also produces a good fit to the interannual variability of the CO growth 2
rate. The current study adds to results obtained by other approaches, even though the results are
not always consistently and should be seen as supporting a better understanding of the different
processes contributing to the terrestrial carbon budget.
On a global scale, NPP is the main contributor to the interannual variability of net ecosystem
production (NEP), whereas its magnitude and timings are mainly determined by heterotrophic
respiration. The interannual variability of global NPP is dominated by tropical regions where it
is mainly a function of variations in precipitation. The temperate and boreal zone NEP
variations are also controlled by changes in NPP, but these are determined by changes in
temperature. Net fluxes are highly correlated to El Niño-Southern Oscillation (ENSO) events in
the tropics and southern mid latitudes, whereas no tele-connection to the northern hemisphere
can be found. An influence of the North Atlantic Oscillation (NAO) on carbon fluxes on a
latitudinal scale could not be detected. During the post-Pinatubo period boreal NEP declined,
whereas the northern temperate regions show an enhanced uptake due to increased NPP and
decreased Rh. Although temperature rise was strongest in the northern latitudes during 2000 to
2002, this was not reflected in an enhanced net terrestrial uptake.
This study presents a way to assess terrestrial carbon fluxes and elucidates the processes
contributing to interannual variability of the terrestrial carbon exchange. Process-based
terrestrial modelling and satellite-observed vegetation data are successfully combined to
improve estimates of vegetation carbon fluxes and stocks. As net ecosystem exchange is the
most interesting and most sensitive factor in carbon cycle modelling and highly uncertain, the
presented results complementary contribute to the current knowledge, supporting the
understanding of the terrestrial carbon budget. IV Abstract
Contents V


CONTENTS



1. INTRODUCTION ........................................................................ 1


2. SCIENTIFIC BASIS .................................................................... 7

2.1 The terrestrial carbon cycle............................................................................................................... 7
2.1.1 Why is it important to look at the terrestrial carbon cycle? ....................................................... 7
2.1.2 Terrestrial carbon processes and components............................................................................ 9