Central Asian Snow Cover Characteristics between 1986 and 2012 derived from Time Series of Medium Resolution Remote Sensing Data Inaugural-Dissertation zur Erlangung der Doktorwürde der Philosophischen Fakultät I der Julius-Maximilians-Universität Würzburg vorgelegt von Dipl. Geograph Andreas Jürgen Dietz aus Hammelburg München, 2013 Erstgutachter: Professor Dr. Christopher Conrad Zweitgutachter: Professor Dr. Jürgen Rauh Tag des Kolloquiums: 18.12.2013 Acknowledgments Acknowledgments The presented thesis was only made possible due to the support of my supervisors, colleagues, and friends. First of all I want to thank Prof. Dr. Christopher Conrad from the University of Würzburg, who assisted in many research questions related to the study re- gion of Central Asia. His extensive knowledge about the situation in place, the water relat- ed issues, the political framework, combined with the most profound experience in the pro- cessing and analysis of remotely sensed data turned out to be all but unpayable. At the same time, I want to thank Prof. Dr. Stefan Dech from the German Remote Sensing Data Center of the German Aerospace Center for the support. His far-reaching experience in the processing and handling of medium resolution remote sensing data – AVHRR in particular – would have been an irreplacebale store of knowledge. Finally, I want to thank Dr. Claudia Künzer from the Department of Land Surface, German Remote Sensing Data Centre of the German Aerospace Center for her continuous assistance and advice, and for allowing me to be part of a most motivating, open-hearted, and cooperative team. All the colleagues from this team also deserve my special thanks and appreciation, notably - though not exclusively - Dr. Tuan Vo Quoc, inspiring with his exhilarant spirit, Dr. Ursula Gessner for supporting me during the realization of my first paper, Igor Klein for his help with the Russian Translation, Dr. Vahid Naemi for his help and comments regarding IDL programming, Dr. Corinne Frey and Patrick Leinenkugel for enduring to share the of- fice with me, and finally my colleagues Malte Ahrens, Manuel Fabritius, Tim Funkenberg, and Marco Ottinger for diversifying discussions and activities also outside the office. I want to thank Gerhard Gesell from the Department of Atmosphere, German Re- mote Sensing Data Center of the German Aerospace Center for his most valuable support during the processing of AVHRR data, the patient introductions to the APOLLO software, and the provision of the required computer infrastructure to facilitate my processing. Further thanks go to Thomas Eiglsperger who supported the study by collecting field data, the colleagues from the German Research Centre for Geoscience (GFZ) in Potsdam who managed and were involved in the CAWa project, the German Ministry of Foreign Affairs for financing this project, as well as all the interns and administrational staff for doing all the work that usually stays all but unnoticed. Finally, I want to thank my parents Gabi and Gunter Dietz for their long-time sup- port. The presented thesis was only made possible due to your patience, assistance, and compliancy for so many years. II III Table of contents Table of contents Acknowledgments ................................................................................................................. II Table of contents ................................................................................................................. IV List of figures ....................................................................................................................... VI List of tables ......................................................................................................................... X Glossary ............................................................................................................................. XII Abstract ............................................................................................................................. XVI Zusammenfassung (Abstract in German) ........................................................................ XVII резюме́ (Abstract in Russian) ......................................................................................... XVIII 1. Introduction and aims of the thesis ................................................................................... 1 2. Region of interest – Central Asia ...................................................................................... 7 2.1 Climate, climate change, and hydrology ...................................................................... 7 2.2 Land cover and topography ....................................................................................... 17 3. Principles of snow cover monitoring using remotely sensed data .................................. 21 3.1 Physical and spectral properties of snow .................................................................. 21 3.2 Methods to map snow using remotely sensed data ................................................... 31 3.2.1 Discrete methods for snow cover mapping with optical sensors ......................... 31 3.2.2 Fractional snow cover algorithms ........................................................................ 40 3.2.3 Algorithms to estimate snow cover below clouds ................................................ 43 3.2.4 Identification of snow cover and SWE with PM sensors ..................................... 45 3.2.5 Combination of PM and reflective data to map snow cover ................................ 50 3.3 Summary and discussion of presented methods ....................................................... 53 3.4 Existing Snow Cover Studies ..................................................................................... 62 3.4.1 Large scale snow cover studies .......................................................................... 62 3.4.2 Small scale snow cover studies .......................................................................... 65 3.4.3 Conclusions: Transferability of the findings to Central Asia ................................ 68 4. Data Sources .................................................................................................................. 70 4.1 AVHRR LAC Level 1B Data ....................................................................................... 70 4.2 MODIS daily snow cover products MOD10A1 and MYD10A1 .................................. 72 4.3 SRTM data ................................................................................................................. 74 4.4 Landsat ...................................................................................................................... 74 4.5 In situ data ................................................................................................................. 76 IV Table of contents 5. Methods .......................................................................................................................... 78 5.1 AVHRR processing .................................................................................................... 78 5.2 Cloud reduction in AVHRR and MODIS snow data ................................................... 81 5.3 Calculation of snow cover parameters ....................................................................... 85 5.4 Accuracy assessment of APOLLO snow products .................................................... 87 5.4.1 Using Landsat and MODIS to assess APOLLO snow product accuracy ............ 87 5.4.2 Comparison of snow depth station data with the APOLLO snow product ........... 89 5.5 Indirect accuracy assessment of cloud free snow products ...................................... 89 5.6 Accuracy assessment using field trip data ................................................................. 92 6. Results and discussion ................................................................................................... 93 6.1 APOLLO snow cover product and accuracy .............................................................. 93 6.2 Snow cover parameters for Central Asia ................................................................. 112 6.2.1 Snow Cover Duration ........................................................................................ 113 6.2.2 Snow Cover Start .............................................................................................. 124 6.2.3 Snow Cover Melt ............................................................................................... 134 6.2.4 Snow Cover Index ............................................................................................. 144 6.2.5 Discussion of snow cover parameters in Central Asia ...................................... 146 6.3 Results from the accuracy assessments ................................................................. 152 6.4. Snow cover development and its influence on transboundary water management 163 6.5. Outlook on possible applications ............................................................................ 165 7. Conclusions .................................................................................................................. 181 References ........................................................................................................................ 184 Eidesstattliche Erklärung ................................................................................................... 208 Tabellarischer Lebenslauf ................................................................................................