This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Chen, Andrew Title: Climatic controls on drainage basin hydrology and topographic evolution General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. However, if you have discovered material within the thesis that you consider to be unlawful e.g. breaches of copyright (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please contact [email protected] and include the following information in your message: •Your contact details •Bibliographic details for the item, including a URL •An outline nature of the complaint Your claim will be investigated and, where appropriate, the item in question will be removed from public view as soon as possible. Climatic controls on drainage basin hydrology and topographic evolution Shiuan-An Chen A dissertation submitted to the University of Bristol in accordance with the requirements for award of the degree of Doctor of Philosophy in the Faculty of Science. School of Geographical Sciences March 2021 Word count: 26,276 Abstract Climate is assumed to influence drainage basin evolution through interactions between rainfall, runoff, and erosion processes. Although former studies have extensively explored climatic controls on land surface processes and landforms, they were mainly targeted humid regions, owing to the lack of data in drylands and limited global databases. In addition, climatic controls tend to covary with other factors, such as vegetation and topography, complicating the detection of climatic signals on landforms. To explore the influences of climate on drainage basin topography across climate zones, this thesis meta-analysed hydrological regimes in the USA, and river longitudinal profile concavity and short- and long- term drainage basin erosion rates around the globe. The data were compiled from published literature and databases and classified by climate classifications. There is a spectrum of downstream changes in water discharge across basin aridity, reflecting different characteristics of rainfall–runoff links between climate zones. These various hydrological regimes control the shapes of river longitudinal profile, which are generally concave-up in all climate zones but systematically straighter with higher aridity. On the other hand, drainage basin erosion rates are influenced by various environmental controls between timescales. Long-term erosion rates are non-linearly related to climate, reflecting the balance between precipitation and vegetation cover. Long-term rates are also enhanced by past glaciation in mid- and high-latitude regions, and positively related to the topography of drainage basin. Short-term rates are dominated by anthropogenic activities and are more detectable in small basins with lower sediment buffering capacity. These results link climate with hydrology and land surface processes, improving our understanding on the influences of climate and climate change on drainage basin evolution. i Acknowledgements Studying the PhD degree is an exciting yet challenging journey, especially studying abroad. I have faced many circumstances and made decisions that I had never done in the past. Fortunately, my supervisors, Dr Katerina Michaelides and Dr Michael Bliss Singer, are very kind, patient, and willing to spend time guiding students. They are not only teachers who taught me how to do research, but also friends who care about my thoughts, my life, and my future, and are always encouraging me. They made my life in Bristol much more comfortable than I would ever imagine. I also appreciate my supervisor, Dr David A. Richards, who taught me the principle of cosmogenic nuclides and helped me improve my study. I thank Prof Rudy Slingerland for providing and modifying the LONGPRO model’s code, and Dr Stuart W. D. Grieve for building the river long profile database and solving the following issues. I appreciate Prof Jim Freer, Prof Rachel Flecker, Dr Anita Ganesan, and Dr Gemma Coxon, who reviewed my works and gave me advices. I also appreciate my colleagues, Rosie Lane and Jeison Sosa, to provide me with ideas and helps for my study. Many thanks to Isaac Kipkemoi, Tamsin Lockwood, and Yinxue Liu. They are my colleagues and best friends who share lives with me, encourage me, and do our common hobbies together. I thank my wife, Ya-Hsiu (Ashley) Chang, who paused her job in Taiwan and came to the UK for me. Without her support, I would not finish my study and would not gain as many experiences in the UK as I did. Huge thanks to my parents. They always support my hobbies and encourage me to study abroad. They did not give me pressure on my study or my life; therefore, I could conduct my research at my own pace and seek my career freely. Finally, I thank God who always create miracles in my life. No matter what challenges I face, what frustrations I have, He always solve my problem and give me more than I ask. iii Author’s declaration I declare that the work in this dissertation was carried out in accordance with the requirements of the University's Regulations and Code of Practice for Research Degree Programmes and that it has not been submitted for any other academic award. Except where indicated by specific reference in the text, the work is the candidate's own work. Work done in collaboration with, or with the assistance of, others, is indicated as such. Any views expressed in the dissertation are those of the author. SIGNED: ............................................................. DATE:.......................... v Table of contents Abstract ................................................................................................................................. i Acknowledgements ............................................................................................................. iii Author’s declaration ............................................................................................................. v Table of contents ............................................................................................................... vii List of tables ........................................................................................................................ xi List of figures .................................................................................................................... xiii Glossary ............................................................................................................................xvii 1. General introduction ......................................................................................................... 1 2. Background and Motivation ............................................................................................. 4 3. Methodology overview ..................................................................................................... 7 4. Links between climate and hydrological regime ............................................................. 11 4.1 Introduction .............................................................................................................. 11 4.2 Methodology ............................................................................................................ 14 4.3 Relationship between ephemerality and downstream distribution of streamflow ..... 18 4.4 Relationship between drainage area and discharge ................................................ 21 4.5 Climatic controls on streamflow characteristics ....................................................... 23 4.6 Chapter summary .................................................................................................... 26 5. Climatic controls on river long profiles globally .............................................................. 28 5.1 Introduction .............................................................................................................. 28 5.1.1 The characteristics and controls of river long profile ....................................... 28 5.1.2 Indices of river long profile concavity .............................................................. 29 5.1.3 Motivations and objectives .............................................................................. 33 5.2 Methodology ............................................................................................................ 33 5.3 Preliminary analyses of manually-extracted river long profiles ................................ 40 5.4 Global analyses of river long profile concavity ......................................................... 43 5.5 Simulating the influences of hydrology on river long profile evolution ...................... 48 5.6 Chapter summary .................................................................................................... 52 6. Climatic controls on drainage