Not all droughts are equal: understanding the climate drivers of wind erosion (ENSO, SAM and IOD) Author Parsons, Katherine Published 2017-08 Thesis Type Thesis (PhD Doctorate) School Griffith School of Environment DOI https://doi.org/10.25904/1912/484 Copyright Statement The author owns the copyright in this thesis, unless stated otherwise. Downloaded from http://hdl.handle.net/10072/373953 Griffith Research Online https://research-repository.griffith.edu.au Not all droughts are equal: understanding the climate drivers of wind erosion (ENSO, SAM and IOD) Katherine Parsons BSc. (Hons) Griffith School of Environment Science, Environment, Engineering and Technology Griffith University Submitted in fulfilment of the requirements of the degree of Doctor of Philosophy August 2017 i Statement of originality This work has not previously been submitted for a degree or diploma in any university. To the best of my knowledge and belief, the thesis contains no material previously published or written by another person except where due reference is made in the thesis itself. (Signed) Katherine Parsons ii iii Abstract Wind erosion is recognised as an important issue globally. It is of importance in Australia due to a large proportion of the continent being classed as arid to semi-arid. With increases in land use and projected increases in the frequency and intensity of drought periods in Australia, wind erosion may be seen to increase, intensify and expand across the continent. Additionally, increases in the severity of annual to inter- annual climate systems (such as the El Niño Southern Oscillation (ENSO), the Southern Annual Mode (SAM), the Indian Ocean Dipole (IOD)) and even in overarching decadal to inter-decadal climate systems (such as the Interdecadal Pacific Oscillation (IPO) and the Pacific Decadal Oscillation (PDO)) will result in the spatial and temporal impacts of wind erosion being altered over time. Variations in drought and climate systems are recognised to affect wind erosion in Australia due to their influences on precipitation and erosive wind systems. Literature in the field of drought, wind erosion and climate systems was reviewed with respect to framing the need for this dissertation. It was identified that although a detailed understanding of drought has been developed over time (including definitions, impacts and influences) there are still challenges associated with the lack of uniform definition and with measures of severity, scale and overall prediction. Few wind erosion studies have focused on the impact that drought may have (and its flow-on effects to other wind erosion variables such as vegetation), particularly with respect to changes in response to climate. Climate systems research presents another layer of complexity to measuring or predicting wind erosion in Australia. This dissertation explores the role of drought and climate systems in wind erosion in eastern Australia (over the past 100 years), comparing a calculation of the potential for wind erosion with actual wind erosion (AWE) measures. It selects and adapts a drought index suitable for use in wind erosion studies and estimates the wind erosion potential (WEP) of eight drought periods, incorporating measures of soil erodibility and wind erosivity. It also evaluates why actual wind erosion rates (according to three different measures) differ to results produced by the WEP and examines how climate systems (the ENSO, SAM and IOD) and synoptic-scale systems influence wind erosion during the drought periods. Two drought indices (rainfall deciles (RD) and the Standardized Precipitation Index (SPI)) were assessed according to seven criteria developed to evaluate the iv favourability of indices for use in wind erosion studies. The SPI was selected as the most favourable due to its ability to identify the start and end dates of drought, provide measures of drought intensity, magnitude and severity and best capture wind erosion activity. The SPI was adapted and enhanced for the calculation of WEP using established factors of drought, erodibility (vegetation cover) and erosivity (wind speed) and applied to historical data (over 100 years from the consolidation of 63 observer stations into 22 stations in eastern Australia. Differences in results were evident for northeastern Australia (NEA) and southeastern Australia (SEA), reflecting varying short and longer term climatic influences. At a localised level wind severity, vegetative cover types and geomorphological features were able to explain differences. Specific climate systems phases (negative ENSO, negative SAM and positive IOD) occurring drought periods were found to favour wind erosion activity (both in NEA and SEA). A combination lock of climate system phase and wind erosion risk was developed to provide a conceptual understanding of the influence of climate systems on wind erosion during drought periods in Australia. This conceptual approach is unique to this dissertation, constituting an original innovation in the field of wind erosion research during drought and climate system studies in general. Combinations of climate system phases and associated wind erosion risk were presented for eight combinatoric scenarios, with highest wind erosion risk associated with negative ENSO, negative SAM and positive IOD. These combinations were demonstrated to have differing impacts according to location on the Australian continent due to differing synoptic-scale system dominance (trough systems in the north and cold fronts in the south). This dissertation has confirmed the important role that climate systems have on wind erosion during drought periods in eastern Australia. Its results have new implications for research in the field of wind erosion. It demonstrates a method of measuring drought from a wind erosion perspective and develops a way of both estimating wind erosion potential risk and investigating wind erosion activity from the lens of climate systems. The combination lock approach to climate systems and wind erosion during drought periods provides a conceptual advance in the climatological and meteorological understanding of wind erosion activity (spatially and temporally). Furthermore, at a time when the future impacts of drought and climate systems are predicted to intensify in severity and spatial scale, this research could provide a way for aeolian geomorphologists and land managers to predict the risk of wind erosion occurrence. v vi Table of Contents Abstract ..................................................................................................................... iv Table of Contents .................................................................................................... vii List of Figures .......................................................................................................... xii List of Tables............................................................................................................ xv Acknowledgements .............................................................................................. xviii Acronyms and Abbreviations ................................................................................. xx Chapter 1 Introduction .............................................................................................. 1 1.1 Preamble ........................................................................................................ 1 1.2 What is already known about drought and climate systems? .......................... 4 1.3 The influence of drought and climate systems on wind erosion....................... 4 1.4 Linkages and knowledge gaps ........................................................................ 5 1.5 Dissertation aims ............................................................................................ 6 1.6 Dissertation structure ...................................................................................... 7 1.7 Selected stations, data types and data sources ............................................ 10 Chapter 2 Understanding wind erosion, drought and climate systems – a literature review ....................................................................................................... 13 2.1 Wind erosion ................................................................................................. 13 2.1.1 Types of wind erosion ............................................................................ 14 2.1.2 Drivers of wind erosion .......................................................................... 17 2.1.3 Source areas, spatial distribution and transport ..................................... 23 2.1.4 Seasonality ............................................................................................ 26 2.1.5 Impacts of wind erosion and dust storm activity ..................................... 27 2.2 Defining drought – Definitions, impacts, influences and indices .................... 31 2.2.1 Conceptual and operational definitions of drought ................................. 33 2.2.2 Causes of and influences on drought ..................................................... 35 2.2.3 Impacts of drought ................................................................................. 37 2.2.4 Quantifying drought – drought indices ................................................... 41 2.2.5 Measuring drought duration, intensity and spatial scale ......................... 45 2.3 Climate systems ..........................................................................................