Assessing Climate Change Impacts on Physical Structure of Lakes and Reservoirs Using One, Two and Three-Dimensional Hydrodynamic Models
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Faculty of Environmental Sciences Assessing climate change impacts on physical structure of lakes and reservoirs using one, two and three-dimensional hydrodynamic models DISSERTATION In fulfilment of the requirements for the academic degree Doctor rerum naturalium (Dr.rer.nat.) Presented by: Chenxi Mi, January 9th 1989 in Shenyang, China Reviewers: Prof. Dr. Dietrich Borchardt Department of Aquatic Ecosystem Analysis and Management Helmholtz Centre for Environmental Research, Magdeburg, Germany Dr. Karsten Rinke Department of Lake Research Helmholtz Centre for Environmental Research, Magdeburg, Germany Prof. Dr. Thomas U. Berendonk Institute of Hydrobiology Technische Universität Dresden, Dresden, Germany Declaration of Conformity I, Chenxi Mi, hereby confirm that this copy conforms with the original dissertation on the topic: “Assessing climate change impacts on physical structure of lakes and reservoirs using one, two and three-dimensional hydrodynamic models” Ort, Datum Unterschrift Table of Contents List of Tables ................................................................................................................................... v List of Figures ................................................................................................................................. vi List of Abbreviations ....................................................................................................................... x 1. Introduction ................................................................................................................................. 1 1.1. Thermal stratification............................................................................................................ 2 1.2. Recent studies on stratification and current research gaps ................................................... 3 1.3. Main research questions and hypotheses .............................................................................. 6 1.3.1. Assessing vertical diffusion in a stratified lake using a 3D hydrodynamic model ........ 6 1.3.2. Stratification dynamics in Rappbode Reservoir under different wind conditions ......... 7 1.3.3. Variable withdrawal elevations as a management tool to counter the effects of climate warming in Rappbode Reservoir ............................................................................................. 7 1.3.4. Ensemble warming projections in Rappbode Reservoir and potential adaptation strategies .................................................................................................................................. 8 2. Assessing vertical diffusion in a stratified lake using a 3D hydrodynamic model ...................... 9 2.1. Abstract ................................................................................................................................. 9 2.2. Introduction .......................................................................................................................... 9 2.3. Materials and Methods ....................................................................................................... 11 2.3.1. Study site ..................................................................................................................... 11 2.3.2. Numerical model ......................................................................................................... 12 2.3.3. Model setup and parameters ........................................................................................ 15 2.3.4. Calculation of vertical turbulent diffusion coefficient Kz............................................ 16 2.3.5. Model performance and uncertainty analysis .............................................................. 17 2.3.6. Scenarios ...................................................................................................................... 17 2.4. Results ................................................................................................................................ 18 2.4.1. Model performance and validity .................................................................................. 18 i 2.4.2. Mixing conditions in the metalimnion ......................................................................... 22 2.4.3. Effects from changing temperature and wind conditions ............................................ 23 2.5. Discussion ........................................................................................................................... 25 2.5.1. Evaluation of the modelling approach ......................................................................... 25 2.5.2. Opportunities and limits of the 3D hydrodynamic model ........................................... 26 2.5.3. Limnological processes and lake ecosystem dynamics ............................................... 27 2.6. Conclusion .......................................................................................................................... 28 3. Stratification dynamics in a reservoir under different wind conditions .................................... 30 3.1. Abstract ............................................................................................................................... 30 3.2. Introduction ........................................................................................................................ 30 3.3. Methods .............................................................................................................................. 32 3.3.1. Study site ..................................................................................................................... 32 3.3.2. Numerical model ......................................................................................................... 33 3.3.3. Model setup and input data .......................................................................................... 33 3.3.4. Model calibration ......................................................................................................... 35 3.3.5. Wind scenarios ............................................................................................................. 35 3.3.6. Evaluation of simulations ............................................................................................ 37 3.4. Results ................................................................................................................................ 38 3.4.1. Calibration results ........................................................................................................ 38 3.4.2. Statistical properties of wind velocity at Rappbode Reservoir .................................... 39 3.4.3. Scenario S1: Stratification phenology in 2015 at different wind conditions ............... 40 3.4.4. Scenario S2: Sensitivity to wind speed under averaged meteorological conditions ... 41 3.4.5. Scenario S3: Effects of short-term wind events on stratification ................................ 42 3.4.6. Scenario S4: Effects of short-term wind events on stratification (seasonally varying) ............................................................................................................................................... 45 3.5. Discussion ........................................................................................................................... 46 4. Variable withdrawal elevations as a management tool to counter the effects of climate ii warming in Germany’s largest drinking water reservoir ............................................................... 49 4.1. Abstract ............................................................................................................................... 49 4.2. Introduction ........................................................................................................................ 49 4.3. Methods .............................................................................................................................. 51 4.3.1. Study site ..................................................................................................................... 51 4.3.2. Numerical models ........................................................................................................ 52 4.3.3. Model setup and input data .......................................................................................... 54 4.3.4. Model calibration ......................................................................................................... 56 4.3.5. Scenarios ...................................................................................................................... 57 4.4. Results ................................................................................................................................ 57 4.4.1. Model calibration ......................................................................................................... 57 4.4.2. Scenario S1: Influencing ice dynamics by withdrawal regime ................................... 60 4.4.3. Scenario S2: Mixing regimes under different withdrawal and warming regimes ....... 61 4.5. Discussion ........................................................................................................................... 63 4.6. Conclusions ........................................................................................................................ 67 5. Ensemble warming projections in Germany's largest drinking