Drought severity estimation under a changing climate

Abstract

This paper describes an approach to estimate drought severity for drought response planning and urban water management considering the impacts of climate change and variability. Low flow frequency analysis was used to estimate drought severity (eg. 1-in-100-year average recurrence interval) of different drought durations from several months to years. Traditionally this was done using available historical streamflow record. However, recent research including the South Eastern Australian Climate Initiative has indicated that the prolonged drought experienced in southeastern Australia including Melbourne in the recent decade since 1997 has been unprecedented in historical context, and is potentially part of a long-term trend associated with global warming. This raises the issue of the practicality of the assumption of hydrologic stationarity. To account for the potential for more severe and frequent drought events, an adaptive approach is needed to adapt to the drier future in a changing and variable climate by considering experience from the recent 1997–2009 drought and the latest climate change projections. In this paper, drought severity for the Melbourne system is estimated based on historical streamflow data with monthly flow prior to 1997 adjusted using a flow duration curve decile method to reflect the recent dry conditions of 1997–2009. The approach is consistent with recommendations in the Victorian Guidelines for the Development of a Water Supply-Demand Strategy (DSE, 2011). The results indicate that drought severity and frequency increased by an order of magnitude under a changed climate based on a “return to dry” scenario. This shift in severity and frequency highlights the need for adaptive planning methods to address changes in hydrologic conditions under a variable and changing climate. However, it also raises many challenges for drought planning including uncertainties in climate change projections, attribution of recent drought to climate change and variability, and the appropriate hydro-climate baseline for applying climate change projections.

Keywords:

• Drought response planning
• water outlook
• adaptive management
• low flow frequency analysis
• critical drought duration and storage drawdown
• climate change and variability
• “return to dry” scenario

Additional information

Notes on contributors

K S Tan

Dr Kim-Seong Tan is a Senior Water Resources Engineer at Melbourne Water. As a member within the Strategic Planning Group, his main focus is to develop and implement strategies to improve water resource management, drought response planning, and adaptation to climate change and variability. With his expertise in catchment hydrology and water resource system assessment, Kim-Seong has recently played a leading role in the development of the new Water Outlook, an adaptive water management approach for Melbourne. Kim-Seong received his Bachelor of Civil Engineering from the University of Technology Malaysia in 1989, Master in Hydrology from University College Galway Ireland in 1994, and PhD in Water Resources from the University of Melbourne in 2004. He is a registered Professional Engineer in Malaysia, spending most of his initial career as a consulting engineer with wide-ranging experience in drainage, flood mitigation, river and coastal engineering projects. In 1999, he embarked on his PhD with a Melbourne Research Scholarship and developed an approach to establish the design flood levels in the Gippsland Lakes that accounts for the joint impacts of atmospheric pressure, wind, rainfall, river floods and coastal tidal levels. Upon completion he was appointed a Research Fellow at the University of Melbourne, prior to joining Melbourne Water in 2006.

B G Rhodes

Bruce Rhodes is the Manager Water Resources at Melbourne Water, Victoria, Australia, and has a professional background of over 30 years in positions in consulting, government and at Melbourne Water. His position at Melbourne Water covers catchment hydrology, water resources data management, water resources modelling, strategic water resource planning, and drought management and climate change adaptation. His professional interests include climate change and variability and short and long term water supply availability and assessment. Bruce is a Civil Engineer and has a Masters in Water Resources and is a member of Engineers Australia. Bruce has authored numerous papers and presented on climate change and water resources management, water resources planning and drought management at many national and international conferences. Bruce currently serves as a member of the American Water Works Association Climate Change Committee, and the Australian Bureau of Meteorology’s Jurisdictional Reference Group for Water Information.