Evidence from the Horn of Africa Sil La
Total Page:16
File Type:pdf, Size:1020Kb
Exploring causality in interactions between climate shifts, land degradation and humans: evidence from the Horn of Africa Sil Lanckriet Proefschrift voorgedragen tot het behalen van de graad van Doctor in de Wetenschappen Geografie Faculteit Wetenschappen Sil Lanckriet Exploring causality in interactions between climate shifts, land degradation and humans: evidence from the Horn of Africa Proefschrift voorgelegd tot het behalen van de graad van Doctor in de Wetenschappen: Geografie 2015-2016 vii Cover: View of the marginal graben and degraded basalt mountains around Lake Ashenge. Photograph taken by Mérielle Van de Graaf (April 2012). viii ix Promoters: Prof. Dr. Jan Nyssen, Department of Geography, Faculty of Sciences, Ghent University, Belgium Dr. Amaury Frankl, Department of Geography, Faculty of Sciences, Ghent University, Belgium Members of the Jury: Prof. Dr. Ben Derudder, Department of Geography, Faculty of Sciences, Ghent University, Belgium (Chair) Prof. Dr. Veerle Van Eetvelde, Department of Geography, Faculty of Sciences, Ghent University, Belgium (Secretary) Prof. Dr. Ir. Ann Verdoodt, Department of Soil Management, Faculty of Bioscience Engineering, Ghent University, Belgium Dr. Jan Moeyersons, Earth Sciences and Natural Hazards, Royal Museum for Central Africa, Belgium Prof. Dr. Piet Termonia, Department of Physics and Astronomy, Faculty of Sciences, Ghent University, Belgium; Royal Meteorological Institute of Belgium Prof. Dr. Haripriya Rangan, School of Geography, Faculty of Science, University of Melbourne, Australia Prof. Dr. Henry Lamb, Department of Geography and Earth Sciences, Aberystwyth University, Wales, UK Dean: Prof. Dr. Herwig Dejonghe Rector: Prof. Dr. Anne De Paepe x xi Aποκλινομένης δὲ μεσαμβρίης παρήκει πρὸς δύνοντα ἥλιον ἡ Αἰθιοπίη χώρη ἐσχάτη τῶνοἰκ εομενέων: αὕτη δὲ χρυσόν τε φέρει πολλὸν καὶ ἐλέφαντας ἀμφιλαφέας καὶ δένδρεαπάντα ἄ γρια καὶ ἔβενον καὶ ἄνδρας μεγίστους καὶ καλλίστους καὶ μακροβιωτάτους. Where south inclines westwards, the part of the world stretching farthest towards the sunset is Ethiopia; this produces gold in abundance, and huge elephants, and all sorts of wild trees, and ebony, and the tallest and longest-lived and handsomest of all people. Ἡρόδοτος, Ἱστορίαι; Herodotos, The History, Muse 3 114.1 (430 BCE) xii xiii Acknowledgements This study could not have existed without the help of many others. First of all, I thank my promoter Prof. Dr. Jan Nyssen for his support and supervision of my fieldworks in Ethiopia, for his advice in Belgium, for answering my many questions and for his zeal for sustainable development in the Ethiopian Highlands. I equally would like to express my gratitude to my co-promoter Dr. Amaury Frankl, for his strong support, help and advice both in Belgium and in Ethiopia. I thank Prof. Dr. Haripriya Rangan for her hospitality in Australia, our pleasant stay in Ethiopia and for the different opportunities she offered me. I thank Dr. Amanuel Zenebe Abraha and Dr. Tesfay Araya for their support in Mekele, Dr. Jean-Luc Schwenninger for his advice and kindliness in Oxford, Dr. Vanessa Gelorini for her advice on the pollen analysis, and all other co-authors for their valuable inputs. Special thanks go to Dr. Tesfaalem Asfaha, Dr. Cornelis Stal, Dr. Nasem Badreldin, Prof. Dr. Ben Derudder and Dr. Miró Jacob for their auxiliary support. Furthermore, this study would not have been possible without the enormous support of Seifu, Gebrekidan, Bereket and Yohannes. Their translations and help on the field have been extremely valuable. The kindliness of the many farmers who helped us or let us work on their fields was astonishing. I am very thankful for their hospitality, as well as for the many invitations to injera and sowa. Their in-depth knowledge of agricultural and environmental management is truly impressive; they taught me so much. To all of them: ክብረት ይሃበለይ! Additionally, I thank Biadgilgn, Etefa, Hailemariam, Zbelo, Romha, Haileselassie, Teshager, Dereje, Tzega, Mulu, Alemou, Gebregeorgis, Haftu, and many others, for supporting me in Ethiopia. Thanks go to Marlies, Sofie, Wouter and Anthony for our xiv pleasant trips in the Highlands. I express my gratitude to the people of the Belgo- Ethiopian VLIR-UOS projects at Mekele University for their important logistical support, and to the Special Research Fund (BOF) of Ghent University and the Flanders Research Foundation (FWO) for the project funding. I thank Helga, Hanne, Hanibal, Marijn and Henok for their help in Ghent. Thanks go to Elizabeth, for proofreading the manuscript and to Lys, for our days in Hagere Selam. Special thanks go to Laurens, who has encouraged me since the first day at university. Last but not least, I cannot forget to thank several other friends, in particular Koen, Feli and all members of De Droge Worsten Groep, KSA Schuiferskapelle, Valuable Tits and Smadders. I owe my deepest thanks to my family; my parents, my brother and my sisters, who are always there for me. Finally, I am deeply grateful to Tasha. In Ghent, Istanbul, Melbourne or Mekele, she has been by my side. Sil, Gent – 29 October 2015 xv Table of Contents Acknowledgements ................................................................................................................................... xiv Table of Contents ....................................................................................................................................... xvi List of Tables .............................................................................................................................................. xxi List of Figures ........................................................................................................................................... xxiii List of Acronyms .......................................................................................................................................... 30 List of Publications ...................................................................................................................................... 33 Abstract ........................................................................................................................................................ 36 Chapter 1 General introduction .................................................................................... 37 1.1 Problem statement ....................................................................................................... 37 1.2 Regional study ............................................................................................................... 39 1.2.1 The Ethiopian Highlands as a representative case study ........................... 39 1.2.2 Sediment characteristics as research proxies.............................................. 41 1.3 Objectives and research questions ............................................................................. 42 1.4 Outline of the thesis ..................................................................................................... 45 1.5 The study area ............................................................................................................... 48 1.6 References ...................................................................................................................... 52 Part I ........................................................................................................................ 58 Chapter 2 Rainfall and drought: modelling the impact of global atmospheric- oceanic teleconnections .............................................................................. 60 2.1 Introduction .................................................................................................................. 63 2.2 Materials and methods ................................................................................................ 66 2.2.1 Climatic background of the study area ......................................................... 66 2.2.2 Pressure and rainfall data ............................................................................... 67 2.2.3 Empirical Orthogonal Teleconnection computations ................................ 68 2.3 Results ............................................................................................................................ 69 2.3.1 Identification of the EOTs ............................................................................... 69 2.3.2 Identification of the inter annual rainfall variability ................................. 71 2.3.3 Linking EOTs with inter annual rainfall variability .................................... 72 2.3.3.1 Single kiremt EOT-logit models ....................................................................... 72 2.3.3.2 A multivariate kiremt model .......................................................................... 72 2.4 Discussion ...................................................................................................................... 74 2.4.1 Physical mechanisms ....................................................................................... 74 2.4.2 Implications for land degradation and climate change ............................. 76 2.5 Conclusions .................................................................................................................... 77 2.6 References ...................................................................................................................... 78 xvi Chapter 3 Hillslope runoff: the impacts of