Modeling terrestrial carbon and water dynamics: a critical appraisal and ways forward

226 Pages·2015·24.21 MB·English

ETH Library
Modeling terrestrial carbon and
water dynamics
A critical appraisal and ways forward
Doctoral Thesis
Author(s):
Pappas, Christoforos
Publication date:
2014
Permanent link:
https://doi.org/10.3929/ethz-a-010384188
Rights / license:
In Copyright - Non-Commercial Use Permitted
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22152
DISS. ETH NO.
MODELING TERRESTRIAL CARBON AND WATER
DYNAMICS: A CRITICAL APPRAISAL AND WAYS
FORWARD
A thesis submitted to attain the degree of
of
DOCTOR OF SCIENCES ETH ZURICH
(Dr. sc. ETH Zurich)
presented by
christoforos pappas
dipl civil eng national technical university of athens
. .
30 1988
born January
citizen of GREECE
accepted on the recommendation of
prof dr paolo burlando examiner
. . ,
prof dr valeriy ivanov co examiner
. . , -
dr simone fatichi co examiner
. , -
2014
ChristoforosPappas:Modelingterrestrialcarbonandwaterdynamics:acriticalappraisaland
ways forward, A thesis submitted to attain the degree of Doctor of Sciences of ETH
2014
Zurich,
Dedicated to the memory
of my beloved mother.

ACKNOWLEDGMENTS
I would like to thank all those people that helped me during the period of my
studies at ETH Zurich and made my time in Switzerland a very nice experience.
Iamgratefultomyadvisor,PaoloBurlandoforhistrustinofferingmethisPhD
position and for his guidance and support during my research. Many thanks go
to Simone Fatichi for his support during the last three years of my research,
for all the fruitful discussions and ideas, but mostly for our disagreements that
made me improve my argumentation. I would like to acknowledge the external
examiner of my thesis, Valeriy Ivanov, who accepted my invitation to review
my work and provided thoughtful comments on my thesis.
I wish also to thank former and current members of the HWRM group of the In-
stituteofEnvironmentalEngineeringforthenicetimewehad.Specialthanksgo
to Grigoris Anagnostopoulos for his generous support during my first months
in Zurich, Marco Carenzo for the nice time inside and outside of the ETH cam-
pus, Stefan Rimkus for helping me with the ‘Zusammenfassung’, and the Silvan
Ragettli, Álvaro Ayala and Simone Schauwecker for all the brainstorming at
KuBaA! I am grateful to Martin Heynen (http://martinheynen.com) for design-
ing the artwork of my thesis cover.
I would like to express my sincere gratitude to Demetris Koutsoyiannis, my
diploma thesis advisor at National Technical University of Athens, for intro-
ducing me to the fascinating world of probability theory and stochastics and
for his support to conduct my doctoral studies abroad. Special thanks go to my
friend,anddiplomathesisco-advisor,Simon-MichaelPapalexiouforthenumer-
ouschallengingdiscussions(scientificandnon-scientific)andforhiscontinuous
encouragement.
Last but not least, I would like to thank my family, my friends in Greece, and
Anna for all our amazing non-PhD-related moments and for their continuous
support and encouragement.
Funding: This study was funded by the Swiss National Science Foundation
61
under the NRP project HydroServ (Vulnerability of hydrological ecosystem
services: Integrative analysis under changes of climate and socio-economy with
4061 125926
an emphasis on adaptation; project no. - ).
v

ABSTRACT
Terrestrial carbon and water balances and their variability under changing cli-
matic conditions and anthropogenic disturbances are topics of great societal
and scientific importance. The role of vegetation in shaping carbon and water
dynamics is of paramount significance. Many numerical models, reflecting dif-
ferent degrees of complexity and abstraction, have therefore been developed to
mimic plant function. The aim of this thesis is to (i) shed light on how vegeta-
tion functioning is simulated in state-of-the-art terrestrial ecosystem models, (ii)
provide a critical appraisal of model strengths and weaknesses, and (iii) present
ways forward to remove some of the identified model limitations.
The first part of the thesis provides a thorough evaluation of a state-of-the-art,
process-based, dynamic vegetation model, LPJ-GUESS, by means of a global
sensitivity analysis. The rationale is that since process-based models embed
physical causalities, the sensitivity of the simulated processes should also re-
flect measurable and observed sensitivities. Having scrutinized the structural
andparameterizationissuesunderlyingLPJ-GUESS,reflectingalsothatofother,
structurally similar dynamic vegetation models, the subsequent parts of the the-
1
sis are devoted to two major model limitations, namely ( ) the lack of spatial
2
representationandsimplifiedsoilwaterhydrology,and( )thelackofecological
realism due to simplified representation of plant trait variability.
The former limitation is analyzed with a novel ecohydrological scheme, D-LPJ,
which is based on an iterative coupling between a spatially explicit, process-
basedhydrologicalmodel(TOPKAPI-ETH)andawell-establisheddynamicveg-
etation model (LPJ). The advantages of D-LPJ over the original, aspatial ap-
proaches of LPJ and LPJ-GUESS are illustrated for a topographically-complex
area located in the central Switzerland. The aggregation-induced biases due to
smoothing of spatial heterogeneities through coarse-grained aspatial represen-
tations are also explicitly quantified.
The second limitation is investigated with an innovative Monte Carlo approach
that is applied to simulate the diversity of plant traits. This approach revises
the broad vegetation categories, based on a discrete and static parameteriza-
tion (named Plant Functional Types), often incorporated in terrestrial ecosystem
models. Proxy plant species are generated using observed multivariate distribu-
tions of coordinated plant traits. Their performance is assessed with a mecha-
nistic ecohydrological model (T&C) across continuous, naturally occurring, me-
teorological gradients in the European Alps. The significant importance of trait-
induced variability in simulating water and carbon dynamics is quantified and
vii
an alternative, probabilistic approach is presented, enhancing the ecological re-
alism within models.
Thelastpartofthethesisprovidesasynthesisoftheaforementionedfindingsto-
gether with a critique of commonly applied approaches for modeling terrestrial
carbonandwaterdynamics.Directionsforfuturemodelimprovementsarehigh-
lighted, combining deterministic with probabilistic concepts, aiming towards a
predictive framework of terrestrial ecosystem functioning.
viii