Impacts of Climate Change on Surface Water in the Onkaparinga Catchment Final Report Volume 1: Hydrological Model Development and Sources of Uncertainty Westra, S., Thyer, M., Leonard, M., Kavetski, D. & Lambert, M. Goyder Institute for Water Research Technical Report Series No. 14/22 www.goyderinstitute.org Goyder Institute for Water Research Technical Report Series ISSN: 1839-2725 Impacts of Climate Change on Onkaparinga: Final Report 1 – Hydrological Model Development The Goyder Institute for Water Research is a partnership between the South Australian Government through the Department of Environment, Water and Natural Resources, CSIRO, Flinders University, the University of Adelaide and the University of South Australia. The Institute will enhance the South Australian Government’s capacity to develop and deliver science-based policy solutions in water management. It brings together the best scientists and researchers across Australia to provide expert and independent scientific advice to inform good government water policy and identify future threats and opportunities to water security. The following Associate organisations contributed to this report: Enquires should be addressed to: Goyder Institute for Water Research Level 1, Torrens Building 220 Victoria Square, Adelaide, SA, 5000 tel: 08-8303 8952 e-mail: [email protected] Citation Westra, S., Thyer, M., Leonard, M., Kavetski, D. & Lambert, M., 2014, Impacts of Climate Change on Surface Water in the Onkaparinga Catchment – Volume 1: Hydrological Model Development and Sources of Uncertainty, Goyder Institute for Water Research Technical Report Series No. 14/22, Adelaide, South Australia. Copyright © 2014 University of Adelaide. To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of the University of Adelaide. Disclaimer The Participants advise that the information contained in this publication comprises general statements based on scientific research and does not warrant or represent the completeness of any information or material in this publication. Page 2 of 104 Impacts of Climate Change on Onkaparinga: Final Report 1 – Hydrological Model Development Table of Contents EXECUTIVE SUMMARY .................................................................................................................................. 7 1 INTRODUCTION ...................................................................................................................................... 10 2 OVERVIEW OF THIS REPORT ............................................................................................................. 11 3 BACKGROUND TO THE ONKAPARINGA CATCHMENT .............................................................. 12 4 DATA TO SUPPORT THE HYDROLOGICAL MODELLING .......................................................... 14 4.1 RUNOFF ................................................................................................................................................. 14 4.2 RAINFALL .............................................................................................................................................. 17 4.3 POTENTIAL EVAPOTRANSPIRATION ....................................................................................................... 21 4.4 MODIFICATIONS TO THE DATA USED SINCE SECOND MILESTONE REPORT .............................................. 23 4.5 SUMMARY OF DATA USED FOR HYDROLOGICAL MODEL CALIBRATION AND VALIDATION ...................... 23 5 QUANTIFICATION OF UNCERTAINTY ............................................................................................. 25 5.1 OVERVIEW ............................................................................................................................................. 25 5.2 BAYESIAN TOTAL ERROR ANALYSIS (BATEA) .................................................................................... 25 5.3 DATA ERRORS ....................................................................................................................................... 27 5.3.1 Input Errors .................................................................................................................................. 27 5.3.2 Output Errors................................................................................................................................ 35 5.4 HYDROLOGICAL MODEL ERRORS .......................................................................................................... 36 5.4.1 Overview of hydrological model GR4J ......................................................................................... 36 5.4.2 Parameter Uncertainty ................................................................................................................. 37 5.4.3 Structural Uncertainty .................................................................................................................. 38 5.5 IMPACT OF HYDROLOGICAL MODEL ERRORS ON PREDICTIONS ............................................................... 39 5.5.1 Evaluating the role of input error on the model parameters ........................................................ 39 5.5.2 Comparing the effect of different sources of uncertainty on the hydrological predictions ........... 42 5.6 SUMMARY OF UNCERTAINTY MODELLING ............................................................................................. 45 6 NON-STATIONARY MODEL DEVELOPMENT ................................................................................. 47 6.1.1 Addressing structural model uncertainty ...................................................................................... 47 Page 3 of 104 Impacts of Climate Change on Onkaparinga: Final Report 1 – Hydrological Model Development 6.1.2 Selecting models for use in the climate change assessment .......................................................... 48 7 SUMMARY AND CONCLUSIONS ......................................................................................................... 53 REFERENCES ................................................................................................................................................... 57 APPENDIX 1: “A STRATEGY FOR DIAGNOSING AND INTERPRETING HYDROLOGICAL NON- STATIONARITY” – MANUSCRIPT UNDER REVIEW WITH WATER RESOURCES RESEARCH . 59 Page 4 of 104 Impacts of Climate Change on Onkaparinga: Final Report 1 – Hydrological Model Development List of Figures Figure 1: Catchments used in the analysis .............................................................. 13 Figure 2: Location of stream gauge sites ................................................................ 15 Figure 3: Data quality at streamflow gauges ........................................................... 16 Figure 4: Rain gauge locations in the Onkaparinga catchment ................................... 18 Figure 5: Scatterplot of the Houlgrave Weir catchment average rainfall with the percentage of missing sites on any given day in the period 1970 onwards. The underlying density (bandwidth=0.5) indicates that there is not a strong relationship between the two variables. “Missing” values are those that did not have an exact total recorded on that day and thus required interpolation by SILO (i.e. accumulations, actual missing or poor quality data). .......................................... 21 Figure 6: Time series of annual total pan evaporation. The ‘corrected’ version of the Mount Bold Reservoir data was based on the recommendation in Teoh [2002] that due to the proximity of the station to a water body and a pine forest in the surrounding area, it was necessary to adjust the records upwards. ..................... 22 Figure 7: Schematic of BATEA ............................................................................... 26 Figure 8: A sample of radar images covering the Onkaparinga Catchment showing different types of rainfall activity ..................................................................... 29 Figure 9: Annual average rainfall observed by Buckland Park radar ........................... 30 Figure 10: Annual average rainfall observed for the period matching the radar. .......... 30 Figure 11: Masked images to obtain true rainfall estimate for relevant subcatchments of the Onkaparinga (Houlgrave Weir Catchment, Scott Creek Catchment, Echunga Catchment). The rainfall gauge locations provide an estimate of the observed rainfall. ........................................................................................................ 32 Figure 12: Multipliers for separate catchments plotted against observed rainfall. ......... 33 Figure 13: Standard deviation of rainfall multipliers for plotted against observed rainfall for each catchment. ...................................................................................... 34 Figure 14: Runoff error time series at Scott Creek. Runoff errors = streamflow predicted by rating curve – streamflow gauging. ............................................................. 36 Figure 15: Structure of GR4J model. Extracted from [Perrin et al., 2003]. .................. 37 Figure 16: Implications of input error on total error for Houlgrave Weir a five-month period in 1996. Blue shading indicates rainfall error, while red shading indicates the residual error model. ....................................................................................