Im Zusammenhang mit dem globalen Klimawandel ist die Vegetation besonders wichtig, da sie die anthropogenen CO2-Emissionen aufnehmen und den Wasser- und Energiekreislauf regulieren kann. Während frühere Forschungsarbeiten wertvolle Einblicke in langfristige Veränderungen des Grüns der Vegetation und in Bezug auf die Reaktion der Vegetation auf steigende Temperaturen und atmosphärisches CO2 lieferten, sind die Wechselwirkungen zwischen Vegetation und Wasser noch immer nicht vollständig verstanden. Tatsächlich hat die Dynamik der Bodenfeuchte in der Wurzelzone einen grundlegenden Einfluss auf die Veränderung des Grüns und die Produktivität der Vegetation. Dennoch sind weder die die Empfindlichkeit der Vegetationsproduktivität gegenüber der Bodenwasserversorgung noch die funktionelle Reaktion der Vegetation (d. h. Photosynthese und Transpiration) auf Bodentrockenheitsepisoden auf globaler Ebene vollständig geklärt worden. Forschungsengpässe sind fehlende globale Beobachtungen von Vegetationsfunktion und Bodenwasservariabilität. Außerdem werden die statistischen Instrumente für die Analyse umfangreicher und vielschichtiger Daten nur unzureichend genutzt, was ein besseres Verständnis der globalen Reaktion der Vegetation auf Wasser verhindert. Gleichzeitig trägt eine bessere Kenntnis der Reaktion der Vegetation auf die Wasserversorgung zu einem besseren Verständnis des terrestrischen Wasserkreislaufs bei. Hydrologische Extremereignisse schädigen die Infrastruktur, können das menschliche Wohlergehen beeinträchtigen und treten Berichten zufolge in vielen Regionen der Welt immer häufiger und intensiver auf. Während ein Konsens über die Bedeutung meteorologischer Faktoren für die Regulierung des Wasserkreislaufs und der damit verbundenen Extremereignisse besteht, ist die Rolle der Vegetationsdynamik und -eigenschaften noch nicht ausreichend erforscht. Ihre stärkere Berücksichtigung in hydrologischen Studien bietet das Potenzial, die Prozesse, die hydrologische Extreme antreiben, genauer zu verstehen. Dadurch kann ein besseres Verständnis der Wechselwirkungen zwischen Vegetation und Wasser im Hinblick auf die Wasserempfindlichkeit der Vegetation und die Rückkopplung der Vegetation auf Klimaextreme die Genauigkeit der Landoberflächenmodellierung verbessern, was für die Verbesserung der Klimaprojektionen unerlässlich ist. Dank der jüngsten Entwicklungen im Bereich der Erdbeobachtung und der Anwendbarkeit leistungsfähiger statistischer Analysewerkzeuge ist es nun möglich, globale Wechselwirkungen zwischen Vegetation und Wasser mit noch nie dagewesener Genauigkeit zu untersuchen. In diesem Zusammenhang stützt sich diese Arbeit insbesondere auf (i) neuartige Datenprodukte wie sonneninduzierte Chlorophyllfluoreszenz oder globale Bodenfeuchte und Evapotranspiration, die aus der Hochskalierung von Stationsmessungen mit Algorithmen des maschinellen Lernens gewonnen wurden, (ii) längere Aufzeichnungen und aktualisierte Aufbereitungen etablierter Datenprodukte wie Blattflächenindex und terrestrische Wasserspeicherung und (iii) die Entwicklung erklärbarer Methoden des maschinellen Lernens, mit denen Informationen effizient aus multivariaten Datenströmen abgeleitet werden können und die darüber hinaus leicht implementier- und in ökohydrologischen Studien anwendbar sind. Basierend auf diesen Datensätzen und Werkzeugen, wird in dieser Arbeit die Empfindlichkeit der globalen Vegetation gegenüber der Bodenwasserversorgung über Raum und Zeit hinweg neu untersucht.:Summary 7 Zusammenfassung 11 1 Introduction 15 1.1 Motivation 16 1.2 Terrestrial vegetation and its relationship with water supply 18 1.2.1 Vegetation functioning 18 1.2.2 Hydro-meteorological drivers of evaporation and vegetation productivity 19 1.2.3 Vegetation structure and physiology 21 1.3 Terrestrial water cycle and its relationship with vegetation 24 1.3.1 Water balance 24 1.3.2 Vegetation regulating the water cycle 26 1.3.3 The relevance of vegetation on hydrological extremes 27 1.4 Advances in observations and models 30 1.4.1 Spaceborne remote sensing 30 1.4.2 Data-driven and physical-based models 34 1.5 Research questions and thesis outline 37 1.5.1 What is the relationship between vegetation productivity and water supply? 37 1.5.2 Can vegetation regulate hydrological extremes? 38 1.5.3 Can land surface models capture vegetation-water interplay? 40 1.5.4 Thesis outline 40 2 Global vegetation controls using multi-layer soil moisture 41 2.1 Introduction 42 2.2 Data and methods 43 2.3 Results and discussion 45 2.4 Conclusions 53 2.A Appendix 54 3 Widespread increasing vegetation sensitivity to soil moisture 70 3.1 Introduction 71 3.2 Data and methods 72 3.3 Results and discussion 78 3.4 Conclusions 85 3.A Appendix 86 4 The drought effect on vegetation physiology inferred from space 101 4.1 Introduction 102 4.2 Data and methods 104 4.3 Results and discussion 111 4.4 Conclusions 122 4.A Appendix 123 5 Drought propagation into the terrestrial water cycle 136 5.1 Introduction 137 5.2 Data and methods 139 5.3 Results and discussion 145 5.4 Conclusions 155 5.A Appendix 157 6 Drivers of high river flows in European near-natural catchments 171 6.1 Introduction 172 6.2 Data and methods 173 6.3 Results and discussion 179 6.4 Conclusion 184 6.A Appendix 186 7 Synthesis 193 7.1 What is the relationship between vegetation productivity and water supply? 194 7.2 Can vegetation regulate hydrological extremes? 197 7.3 Can land surface models capture the observed vegetation-water interplay? 199 7.4 Limitations 200 7.4.1 Difficulties in predicting SIF in tropical regions 200 7.4.2 Observing terrestrial photosynthesis and evaporation 201 7.4.3 Methods related to variable importance quantification 202 7.5 Outlook 202 7.5.1 Vegetation sensitivity to soil moisture and its implications 203 7.5.2 Vegetation functioning and related structure and physiology 203 7.5.3 Extreme events: floods and drought 204 References 206 Statement of authorship contributions 238 Acknowledgements 239 Curriculum Vitae 241 Scientific publications 242 IMPRS certificate 244 / In the context of global climate change, vegetation is particularly relevant as it can take up anthropogenic CO2 emissions and regulate water and energy cycling. While previous research provided valuable insights into long-term changes in vegetation greenness and in terms of the vegetation response to increasing temperature and atmospheric CO2, vegetation-water interactions are still not fully understood. In fact, root-zone soil moisture dynamics have a fundamental influence on modulating vegetation greenness and productivity. Nevertheless, neither the sensitivity of vegetation productivity to soil water supply nor the vegetation functional response (i.e., photosynthesis and transpiration) to soil drought episodes have been fully resolved at the global scale. Missing global observations of vegetation functioning and terrestrial water variability are bottlenecks, and statistical tools for analyzing large and multi-stream data are poorly exploited, preventing a better understanding of global vegetation water response. At the same time, a better knowledge of the vegetation response to the water supply in turn advances the understanding of the terrestrial water cycle. Hydrological extremes are damaging infrastructure and can affect human well-being, and have been reported to become more frequent and intense in many regions around the world. While a consensus exists regarding the importance of meteorological drivers for regulating the water cycle and related extreme events, the role of vegetation dynamics and characteristics is understudied. Its greater consideration in hydrological studies offers the potential to more accurately understand the processes driving hydrological extremes. Thereby, a better understanding on vegetation-water interactions in terms of vegetation water sensitivity and vegetation feedbacks on climate extremes can advance the accuracy of land surface modelling which is essential to improve climate projections. Thanks to recent developments in Earth observations and in the applicability of powerful statistical analyses tools, investigating global vegetation-water interactions is now possible with unprecedented accuracy. In this context, this thesis builds particularly on (i) novel data products such as Sun-induced chlorophyll fluorescence or global gridded soil moisture and evapotranspiration products obtained from upscaling station measurements with machine learning algorithms, (ii) longer records and updated processing of established data products such as leaf area index and terrestrial water storage, and (iii) the development of explainable machine learning methods which can efficiently derived information from multivariate data streams, and are furthermore implemented and readily applicable in ecohydrological studies. With these datasets and tools, this thesis revisits the sensitivity of global vegetation to soil water supply across space and time.:Summary 7 Zusammenfassung 11 1 Introduction 15 1.1 Motivation 16 1.2 Terrestrial vegetation and its relationship with water supply 18 1.2.1 Vegetation functioning 18 1.2.2 Hydro-meteorological drivers of evaporation and vegetation productivity 19 1.2.3 Vegetation structure and physiology 21 1.3 Terrestrial water cycle and its relationship with vegetation 24 1.3.1 Water balance 24 1.3.2 Vegetation regulating the water cycle 26 1.3.3 The relevance of vegetation on hydrological extremes 27 1.4 Advances in observations and models 30 1.4.1 Spaceborne remote sensing 30 1.4.2 Data-driven and physical-based models 34 1.5 Research questions and thesis outline 37 1.5.1 What is the relationship between vegetation productivity and water supply? 37 1.5.2 Can vegetation regulate hydrological extremes? 38 1.5.3 Can land surface models capture vegetation-water interplay? 40 1.5.4 Thesis outline 40 2 Global vegetation controls using multi-layer soil moisture 41 2.1 Introduction 42 2.2 Data and methods 43 2.3 Results and discussion 45 2.4 Conclusions 53 2.A Appendix 54 3 Widespread increasing vegetation sensitivity to soil moisture 70 3.1 Introduction 71 3.2 Data and methods 72 3.3 Results and discussion 78 3.4 Conclusions 85 3.A Appendix 86 4 The drought effect on vegetation physiology inferred from space 101 4.1 Introduction 102 4.2 Data and methods 104 4.3 Results and discussion 111 4.4 Conclusions 122 4.A Appendix 123 5 Drought propagation into the terrestrial water cycle 136 5.1 Introduction 137 5.2 Data and methods 139 5.3 Results and discussion 145 5.4 Conclusions 155 5.A Appendix 157 6 Drivers of high river flows in European near-natural catchments 171 6.1 Introduction 172 6.2 Data and methods 173 6.3 Results and discussion 179 6.4 Conclusion 184 6.A Appendix 186 7 Synthesis 193 7.1 What is the relationship between vegetation productivity and water supply? 194 7.2 Can vegetation regulate hydrological extremes? 197 7.3 Can land surface models capture the observed vegetation-water interplay? 199 7.4 Limitations 200 7.4.1 Difficulties in predicting SIF in tropical regions 200 7.4.2 Observing terrestrial photosynthesis and evaporation 201 7.4.3 Methods related to variable importance quantification 202 7.5 Outlook 202 7.5.1 Vegetation sensitivity to soil moisture and its implications 203 7.5.2 Vegetation functioning and related structure and physiology 203 7.5.3 Extreme events: floods and drought 204 References 206 Statement of authorship contributions 238 Acknowledgements 239 Curriculum Vitae 241 Scientific publications 242 IMPRS certificate 244

In this study, climate and vegetation interactions are examined for several periods of the geological past with (1) a dynamic global vegetation model CARAIB, and (2) an Earth system model of intermediate complexity Planet Simulator. Both models interact through an equilibrium asynchronous coupling procedure, which consists of a series of iterations of climate and vegetation equilibrium simulations. The climate and vegetation models, as well as the coupling technique developed here and some basic results are rst presented. The models are then applied to study three periods that have experienced large scale climate and vegetation changes: the Last Glacial Maximum, the Middle Pliocene and the Middle Miocene. First, the implications of changing land surface properties on the climate at the Last Glacial Maximum (LGM) are studied. A series of sensitivity experiments is carried out to evaluate the contribution of vegetation change relative to the contributions of the ice sheet expansion and elevation, and the lowering of the atmospheric CO2 on the Last Glacial Maximum climate. We find that the vegetation cover change at the LGM leads to signicant global cooling, together with a decrease in precipitation. The change in the vegetation cover also reinforces the cooling due to other surface cover changes, such as the ice-cover, when applied together with them. Secondly, the climate and vegetation models are used to investigate the Middle Pliocene and Middle Miocene climates and vegetations. Both periods are characterised by a warmer and wetter than present-day climate, and as a consequence, by a reduction of desert areas and an expansion and densification of forests especially at high latitudes. Our results show that the vegetation feedback on climate may have contributed to maintain and even to intensify the warm and humid conditions produced by the other climatic factors at the Middle Pliocene and Middle Miocene. Thus, considering the climate and vegetation interactions could help to reconcile model results with proxy-based reconstructions. This also suggests that vegetation-climate interactions could provide a complementary, if not an alternative mechanism,to the large increase of CO2 required by the models to produce the estimated warming at both periods. The results presented in this study highlight the contribution of the biosphere in past climate changes, and therefore emphasise the study of climate and vegetation interactions to better understand past, present and future climate changes. Furthermore, our results also illustrate that considering the vegetation feedback on climate helps to improve the comparison of climate modelling results to proxy-based reconstructions for the studied periods. Ce travail a pour objet l'étude des interactions entre la végétation et le climat au cours de plusieurs périodes du passé géologique de la Terre, à l'aide (1) du modèle dynamique global de végétation CARAIB, et (2) du modèle climatique de complexité intermédiaire Planet Simulator. Les modèles de végé- tation et de climat interagissent via une procédure de couplage asynchrone à l'équilibre. Dans ce travail, les modèles ont été appliqués à l'étude de trois périodes passées, caractérisées par un changement du climat et de la couverture de végétation à grande échelle : le Dernier Maximum Glaciaire, le Pliocène Moyen et le Miocène Moyen. Dans un premier temps, nous avons étudié l'impact de changements des propriétés de surface continentale sur le climat du dernier maximum glaciaire. Un ensemble de tests de sensibilité a été réalisés à l'aide du modèle climatique afin d'évaluer les contributions relatives de changements dans la couverture de végétation, d'une expansion des calottes de glace et d'une augmentation de leur élévation, et d'une diminution de la concentration de dioxyde de carbone dans l'atmosphère. Les résultats obtenus permettent de mettre en évidence l'impact non-négligeable du changement de végétation sur le climat. Ce dernier changement provoque en effet une diminution des températures, accompagnée d'une réduction des précipitations en moyenne globale. De plus, le changement de végétation renforce les refroidissements obtenus, lorsqu'il est combiné aux autres modifications de la couverture de surface. D'autre part, nous avons modélisé les climats et distributions de végétation du Pliocène Moyen et du Miocène Moyen. Les résultats obtenus témoignent d'un climat plus chaud et plus humide que le climat actuel au cours de ces deux périodes, et par conséquent, d'une réduction des écosystèmes désertiques au profit d'une expansion et densification des écosystèmes forestiers, particulièrement aux hautes latitudes. Ces résultats sont en bon accord avec les résultats de précédentes études de modélisation, ainsi qu'avec les observations. Nos résultats montrent également que la rétroaction de la végétation, en réponse au changement climatique, peut avoir contribué à maintenir, et même à intensier, les conditions chaudes et humides au Pliocène Moyen et au Miocène Moyen produites par les autres facteurs climatiques. Cela suggère également que les interactions végétation-climat pourraient constituer un mécanisme complémentaire, si pas alternatif, à l'importante augmentation de la concentration de CO2 atmosphérique requise par les modèles pour produire les réchauffements estimés aux périodes considérées, et dès lors réconcilier les résultats de modélisation et les estimations basées sur les données, notamment pour Miocène Moyen. Cette étude souligne donc l'importance du rôle joué par la biosphère dans les changements climatiques passés, ainsi que la nécessité de la prise en compte des interactions végétation-climat lors de la simulation de climats passés à l'aide de modèles climatiques et de végétation. De plus, les résultats obtenus montrent, du moins pour les périodes étudiées ici, que la prise en compte des rétroactions de la végétation sur le climat aident à améliorer la comparaison des résultats de modélisation aux reconstructions basées sur des données.

Thesis (Ph.D.)--University of Adelaide, Dept. of Geographical and Environmental Studies, 2001. / Includes bibliographical references (p. 301-319).

In 2011 Manitoba experienced an extreme flood. The operation of the Assiniboine River Diversion resulted in the addition of approximately 1.72 million cubic decameters of water to Lake Manitoba and an increase in water levels to 1.5 m above normal. Although this event resulted damage to farmland and many local homes, it also provided me the unique opportunity to utilize previously impractical methods of bathymetric and substrata distribution analysis in the adjoining Delta Marsh. Combined with satellite imagery taken in 2011 I was able to classify the vegetation classes within the study area and explore the relationship between vegetation distributions and water depth as well as those between water depth and substrata distribution. A seed bank study was carried out to explore the diversity of viable seeds in the area. In addition, satellite imagery taken in 2009 was used to evaluate the effects of the flood event experienced in 2011. / October 2015