Fakultät für Umwelt und Natürliche Ressourcen Professur für Hydrologie der Albert-Ludwigs-Universität Freiburg i. Br. Christoph Ries Streamflow drought characteristics in Australia Referentin: Prof. Dr. Kerstin Stahl Koreferent: apl. Prof. Dr. Jens Lange Master thesis (MSc Environmental Sciences) Freiburg im Breisgau, Mai 2017 Content List of Figures .......................................................................................................................... III List of Maps ............................................................................................................................ III List of Tables ........................................................................................................................... IV List of Annex ........................................................................................................................... IV Keywords ................................................................................................................................ V Abstract ................................................................................................................................. VII Zusammenfassung ................................................................................................................ VIII 1 Introduction ...................................................................................................................... 1 1.1 A short history of drought in Australia ............................................................................... 2 1.2 Climate drivers related to droughts in Australia ................................................................ 3 1.3 Climate change in Australia and repercussions on the hydrosphere................................. 5 1.3.1 Streamflow trends in Australia ....................................................................................... 5 1.3.2 Effects of temperature and evapotranspiration on streamflows .................................. 6 2 Data and study area .......................................................................................................... 9 2.1 Selection criteria for streamflow data .............................................................................. 10 2.2 Processing of precipitation, evapotranspiration and WB data ........................................ 10 2.3 Climate zones in Australia ................................................................................................ 11 2.4 Southeast Australia (Melbourne region) .......................................................................... 13 2.4.1 Hydroclimate at sample station: Murrindindi River ..................................................... 15 3 Methods ......................................................................................................................... 17 3.1 Part I: Characterizing droughts through indicators .......................................................... 17 3.1.1 Correlating meteorological and hydrological drought indicators ................................ 18 3.1.2 The role of accumulation periods ................................................................................ 19 I 3.2 Part I: Calculating the indicator: SPI, SPEI and SSI ............................................................ 19 3.3 Part I: Correlating meteorological and hydrological signals............................................. 20 3.4 Part II: Low flow model and linear trend analysis ............................................................ 21 4 Results ............................................................................................................................ 25 4.1 Part I: All-year indicator performance .............................................................................. 25 4.2 Part I: Seasonal evolution of SPEI correlation strength and response times ................... 33 4.3 Part II: Low flow model ..................................................................................................... 35 4.3.1 Example: Murrindindi River .......................................................................................... 35 4.3.2 All 76 streamflows stations in the Melbourne region .................................................. 39 5 Discussion ....................................................................................................................... 45 5.1 Part I: Are meteorological drought indicators related to streamflow anomalies in Australia? ..................................................................................................................................... 45 5.2 Part II: Are meteorological drought indicators related to the occurrence of low flow in southeast Australia? .................................................................................................................... 50 5.3 Part II: Are meteorological drought indicators related to the occurrence of low flow at the Murrindindi River? ....................................................................................................................... 53 5.4 Influence of autocorrelation ............................................................................................. 54 6 Conclusions ..................................................................................................................... 57 7 References ...................................................................................................................... 59 8 ANNEX ............................................................................................................................ 67 Abbreviations ........................................................................................................................ 70 Symbols ................................................................................................................................. 71 Ehrenwörtliche Erklärung ....................................................................................................... 72 II List of Figures Figure 1: Main climatic drivers of the Australian continent ......................................................... 3 Figure 2: Working process for part II of the thesis: from low flow model to linear trend analysis. ........................................................................................................................ 22 Figure 3: Boxplots showing the absolute difference between SPImaxcor and SPEImaxcor for the stations in Darwin (northwest), Brisbane (east) and Melbourne (southeast). ............ 27 Figure 4: Boxplots: Differences in annual correlation strength (SPI – SPEI) per accumulation period for the stations in the Melbourne region. ........................................................ 30 Figure 5: Boxplots: Differences in annual correlation strength (SPI~SSI – SPEI~SSI) per accumulation period for the stations in the Melbourne region. ................................. 31 Figure 6: Response times (SPEI n, left) and maximum correlation strength (Spearman’s rho, right) for selected stations of the Melbourne region, by season. ............................... 33 Figure 7: Binary flow model for Murrindindi River (ID 178) in southeast Australia (Melbourne region) .......................................................................................................................... 35 Figure 8: Modelled likelihood of Murrindindi River as a function season specific SPEI time series from January 1975 to December 2014. ....................................................................... 37 Figure 9: Goodness of fit (AUC) for all 76 stations in the Melbourne region per season. .......... 39 Figure 10: Boxplots of seasonal AUC values for all 76 stations in the Melbourne region. ........... 40 Figure 11: Summary of the seasonal trend analysis. .................................................................... 42 Figure 12: Annual autocorrelation in SPEI time series at station 178 (Murrindindi River), top: SPEI-1, bottom: SPEI-24................................................................................................ 54 Figure 13: Seasonal autocorrelations (by the example of autumn) in SPEI time series at station 178 (Murrindindi River), top: SPEI-1, bottom: SPEI-24. ............................................... 55 List of Maps Map 1: Spatial distribution of the 222 hydrologic reference stations. ...................................... 9 Map 2: Distribution of the streamflow stations (black dots) over the Koeppen-Geiger climate zones (Peel et al., 2007). .............................................................................................. 11 Map 3: Location of the 76 streamflow stations of the Melbourne region. ............................. 13 III Map 4: Location of the Murrindindi River and its reference station (white circle, zoomed map on right) in southeast Australia. ................................................................................... 15 Map 5: Indicator with the highest maximum correlation with SSI (all-year). .......................... 25 Map 6: Performance differences between SPI (blue) and SPEI (red). ...................................... 26 Map 7: Maximum all-year correlation strength of SPI/SPEI vs SSI. .......................................... 28 Map 8: Accumulation period with highest SPImaxcor/SPEImaxcor (response times). .................... 29 Map 9: Spatial distribution of the flow10 likelihood trends, for stations of the