Regionalization of Parameters of a Conceptual Rainfall-Runoff Model Von der Fakultät Bau- und Umweltingenieurwissenschaften der Universität Stuttgart zur Erlangung der Würde eines Doktors der Ingenieurwissenschaften (Dr.-Ing.) genehmigte Abhandlung Vorgelegt von Yeshewatesfa Hundecha Hirpa aus Addis Abeba, Äthiopien Hauptberichter: Prof. Dr. rer. nat. Dr.-Ing. András Bárdossy Mitberichter: Prof. Dr.-Ing. Axel Bronstert Tag der müdlichen Prüfung: 26. November 2004 Institut für Wasserbau der Universität Stuttgart Stuttgart 2005 2 Heft 142 Regionalization of Parameters of a Conceptual Rainfall-Runoff Model von Dr.-Ing. Yeshewatesfa Hundecha Hirpa Eigenverlag des Instituts für Wasserbau der Universität Stuttgart 3 D93 Regionalization of Parameters of a Conceptual Rainfall- Runoff Model CIP-Titelaufnahme der Deutschen Bibliothek Hundecha Hirpa, Yeshewatesfa: Regionalization of Parameters of a Conceptual Rainfall-Runoff Model / von Yeshewatesfa Hundecha Hirpa. Institut für Wasserbau, Universität Stuttgart. – Stuttgart: Inst. für Wasserbau, 2005 (Mitteilungen / Institut für Wasserbau, Universität Stuttgart: H. 142) Zugl.: Stuttgart, Univ., Diss., 2005 ISBN 3-933761-45-X NE: Institut für Wasserbau <Stuttgart>: Mitteilungen Gegen Vervielfältigung und Übersetzung bestehen keine Einwände, es wird lediglich um Quellenangabe gebeten. Herausgegeben 2005 vom Eigenverlag des Instituts für Wasserbau Druck: Sprint-Digital-Druck GmbH, Stuttgart 4 Acknowledgement I would like to express my gratitude to all those who helped me in one way or another in the course of my journey to complete this work. My special thanks are due to Prof. András Bárdossy for giving me the opportunity to work in his team and helping me set up a direction for this work. Without him, this work wouldn’t have been realised. His guidance and invaluable advices have greatly helped me finish this work with ease. Indeed, his experiences in the field and his multidisciplinary view have helped me take the proper route whenever I found myself at a crossroads in the course of my work. I also owe a sincere gratitude to Prof. Axel Bronstert for his willingness to co-supervise my work and his invaluable comments and suggestions on the work. Finally, I would like to extend my thanks to members of the Institut für Wasserbau for the exciting work environment I enjoyed while working at the institute. 5 6 Table of contents List of Figures ................................................................................................... III List of Tables....................................................................................................... V Abstract ............................................................................................................VII Kurzfassung .......................................................................................................IX 1 Introduction .................................................................................................. 1 1.1 Modelling of the hydrologic cycle ............................................................................. 1 1.2 Challenges of the modelling process.......................................................................... 3 1.3 Modelling ungauged catchments and prediction of the effect of changes ................. 5 1.4 Objective of the study ................................................................................................ 7 2 Study area and data organization............................................................... 8 2.1 Description of the study area...................................................................................... 8 2.2 Organization of data................................................................................................. 12 2.2.1 Meteorological data.......................................................................................... 12 2.2.2 Evapotranspiration ........................................................................................... 22 3 Modelling of the rainfall-runoff processes...............................................25 3.1 Introduction .............................................................................................................. 25 3.2 Selection of appropriate model for the study ........................................................... 26 3.3 Structure of the HBV-IWS model............................................................................ 27 3.3.1 Distributed runoff generation Processes .......................................................... 27 3.3.2 Lumped runoff response process...................................................................... 30 3.3.3 Additional components .................................................................................... 32 3.4 Classification of the subcatchment into homogeneous units for distributed modelling of the runoff generation processes ...................................................................... 34 4 Regionalization of model parameters.......................................................36 4.1 Introduction .............................................................................................................. 36 4.2 A transfer function approach for parameter regionalization .................................... 37 I 4.2.1 Defining the transfer function .......................................................................... 38 4.2.2 Estimation of the parameters of the transfer function...................................... 40 4.2.3 Application of the calibration procedure.......................................................... 45 4.2.4 Validation of the regionalized model............................................................... 56 4.2.5 Sensitivity Analysis.......................................................................................... 67 4.2.5.1 Sensitivity to model parameters ................................................................... 67 4.2.5.2 Sensitivity to input variables........................................................................ 74 5 Application in quantifying the hydrologic effect of land use changes...77 5.1 Introduction .............................................................................................................. 77 5.2 Mathematical modelling of the effect of changes in land use.................................. 77 5.3 Land use scenarios ................................................................................................... 79 5.3.1 Intensive urbanization...................................................................................... 79 5.3.2 Afforestation..................................................................................................... 82 5.3.3 Future land use scenario................................................................................... 85 6 Conclusions and outlook............................................................................90 References ..........................................................................................................94 II List of Figures Figure 2.1 The Rhine basin subdivided into higher meso-scale subcatchments ...................... 9 Figure 2.2 Topographic elevation of the study area in meters above sea level ( Source: The International Commission for the Hydrology of the Rhine basin, CHR). ..... 10 Figure 2.3 Land cover (1993) within the study area (source: The International Commission for the Hydrology of the Rhine basin, CHR)................................... 11 Figure 2.4 Plots of the distance between stations versus 1-r and the corresponding fitted theoretical variograms for precipitation and temperature interpolation................ 17 Figure 2.5 Distribution of precipitation and temperature stations used in the study.............. 18 Figure 2.6 Mean annual precipitation and mean annual temperature in the study area as estimated using the external drift kriging.............................................................. 20 Figure 2.7 Distribution of mean temperature and amount of precipitation on days of extreme temperature/precipitation......................................................................... 21 Figure 3.1 Smoothing of the generated runoff Qg to obtain Q ............................................... 32 Figure 3.2 Schematic representation of the HBV-IWS model ............................................... 33 Figure 4.1 Scatter plots of the model simulated and the observed daily discharges over the model calibration period at gauges where the model performances are the best and the worst respectively.............................................................................. 53 Figure 4.2 Simulated and observed daily discharge hydrographs at two of the gauges located in the calibration set of subcatchments over the year in which there was an extreme flood event................................................................................... 55 Figure 4.3 Scatter plots of the model simulated and the observed daily discharges over the model validation period at gauges where the model performances are the best and the worst respectively.............................................................................. 58 Figure 4.4 Simulated and observed hydrographs at selected gauges in the calibration set of subcatchments in the validation period............................................................. 59 Figure 4.5 Scatter plots of the model simulated and the observed daily discharges at selected