Characterisation of Dust Sources in Central Asia Using Remote Sensing PhD in Environmental Science School of Archaeology, Geography and Environmental Science (SAGES) Mohamad Nobakht September 2017 Declaration of original authorship Declaration: I confirm that this is my own work and the use of all material from other sources has been properly and fully acknowledged. Mohamad Nobakht Acknowledgement This thesis was carried out at the Department of Geography and Environmental Science of the University of Reading, from 2013 to 2017. It was financed by the University of Reading International Research Studentships Award. I wish to express my sincere appreciation to those who have contributed to this thesis and supported me in one way or the other during this amazing journey. Firstly I would like to express my special appreciation and gratitude to my supervisors Dr. Maria Shahgedanova and Dr. Kevin White for the continuous support during my PhD study and their guidance, patience and immense knowledge. I also remain indebted for Maria’s understanding and support during the times when I was really down due to personal family problems. Her advice and encouragement has allowed me to grow both professionally and personally and this has been priceless. Besides my supervisors, I would like to thank my thesis examiners for their insightful comments and for letting my viva be an enjoyable experience. My sincere gratitude is reserved for Dr. Matthew Baddock for his invaluable insights and suggestions. A very special thanks goes out to the University of Reading for giving me the opportunity to carry out my doctoral research and for their financial support. And finally, last but by no means least, I would like to thank my family for their support, especially my wife, Sarah. Words cannot express how grateful I am for all of the sacrifices that you have made. I am truly thankful for having you in my life. Page | II Abstract Central Asian deserts are a significant source of dust in the middle latitudes, where economic activity and the health of millions of people are affected by dust storms. Detailed knowledge of sources of dust, controls on their activity, seasonality and atmospheric pathways are of crucial importance but to date, these data are limited. This thesis presents a detailed database of sources of dust emissions in Central Asia, from western China to the Caspian Sea, obtained by a multi-scale analysis of the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. The multi-scale approach consists of the following steps: 1) MODIS Deep Blue Aerosol Optical Depth (DB AOD) at 10 km resolution, acquired between 2003 and 2014, is used to investigate the spatiotemporal distribution of dust hotspots. 2) A dust enhancement algorithm was employed to obtain two composite images (Dust Enhancement Product, DEP) per day at 1 km resolution from MODIS Terra/Aqua acquisitions between 2003 and 2012, from which dust point sources (DPS) were detected by visual analysis of dust plumes and recorded in a database together with meteorological variables at each DPS location derived from the ERA-Interim reanalysis dataset. In all, more than 13500 DPS were identified. Using this multi-scale approach we provided a high resolution inventory of dust sources at sub-basin scale for Central Asia. Our analysis revealed several active source regions, the most active of which are the eastern part of the Taklmakan desert. An important finding was an increase in dust activity in the newly-formed desert of the Aralkum. Several of the identified dust source regions were not previously identified (e.g. sources in northern Afghanistan) or were not widely discussed in literature before (e.g. the Pre-Aral region in western Kazakhstan). Investigation of land surface characteristics and meteorological conditions at each source region revealed mechanisms for the formation of dust sources, including rapid desiccation of water bodies (e.g. Aral Sea), deflation of dust from fluvial sources (e.g. the Upper Amudarya region) and post-fire wind erosion (e.g. Pre-Aral and Lake Balkhash basins). Different seasonal patterns of dust emissions were observed as well as inter-annual trends. Comparison of DB AOD and DPS revealed a noticeable spatial bias in the AOD-based methods for detection of dust sources which is attributed to the fact that the highest atmospheric dust loadings are not always observed over the dust point sources. Page | III Table of Contents List Of Tables………………………………………………………………………………………….…….VII List Of Figures……………………………………………………………………………………………...VIII Introduction .............................................................................................. 1 1.1.Overview ......................................................................................................... 1 1.2.Research Questions and Thesis Structure .................................................... 2 Literature Review ...................................................................................... 4 2.1.Dust in the Climate System ............................................................................ 4 2.1.1.Dust Impacts on Glaciated Environments ............................................. 6 2.2.Satellite and ground-based remote sensing of dust ..................................... 7 2.2.1.AERONET (Aerosol Robotic Network) ................................................... 8 2.2.2.TOMS (Total Ozone Mapping Spectrometer) ..................................... 11 2.2.3.MODIS (Moderate Resolution Imaging Spectroradiometer) .............. 13 2.2.4.CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) ............. 17 2.2.5.POLDER (POLarization and Directionality of the Earth Reflectance) . 19 2.2.6.SEVIRI (Spinning Enhanced Visible and Infrared Imager) ..................... 20 2.2.7.Summary ............................................................................................... 21 2.3.Central Asia ................................................................................................... 22 2.4.Dust source regions in Central Asia ............................................................. 25 2.4.1.Karakum Desert .................................................................................... 26 2.4.2.Kyzylkum Desert ................................................................................... 28 2.4.3.Aral Kum ................................................................................................ 28 Page | IV 2.4.4.Taklamakan Desert ............................................................................... 30 2.4.5.Gurbantunggut Desert ......................................................................... 35 2.4.6.Balkhash Depression ............................................................................ 36 2.5.Conclusion .................................................................................................... 38 Data and Methodology ........................................................................... 40 3.1.Introduction .................................................................................................. 40 3.2.Aeorosol Optical Depth ................................................................................ 44 3.2.1.Data Access and Pre-Processings ....................................................... 44 3.2.2.Dust Hotspot Detection ....................................................................... 46 3.2.3.Uncertainties ........................................................................................ 49 3.3.Dust Enhancement Technique ..................................................................... 49 3.3.1.MODIS Dust Enhancement Products .................................................. 50 3.3.2.Point Source Detection ........................................................................ 53 3.3.3.Uncertainties ........................................................................................ 57 Chapter 4.Dust hotspot detection using MODIS AOD ........................................... 59 4.1.Introduction .................................................................................................. 59 4.2.Frequency of Occurrence (FO) ..................................................................... 59 4.3.Inter-annual variability of dust loading ........................................................ 62 4.4.Summary ....................................................................................................... 65 Chapter 5.Dust emission point source inventory ................................................... 67 5.1.Introduction .................................................................................................. 67 5.2.Spatiotemporal distribution of dust point sources in Central Asia............. 67 5.3.Dust source regions ..................................................................................... 73 Page | V 5.3.1.Aralkum ................................................................................................. 74 5.3.2.Karakum and Kyzylkum ......................................................................... 83 5.3.3.Taklamakan ........................................................................................... 91 5.3.4.Pre-Aral ................................................................................................. 98 5.3.5.Other source regions .......................................................................... 104 Discussion ............................................................................................