Storage dynamics

This part of my research focuses on analysing the behaviour of catchments during periods of multi-year drought, particularly in south-eastern Australia. This region was affected by a severe drought between 1997 and 2009, known as the Millennium drought. The drought had a significant impact on the region’s hydrology, with many catchments experiencing changes in their annual rainfall-runoff relationships. The aim of this portion of my research is to understand how these changes affected catchment storage, and how this can be characterised using recession analysis. Recession analysis examines how streamflow in a catchetment decrease during periods without rain. This can provide insight into how the catchment’s groundwater dynamics behave, and how surface water interacts with groundwater.

For this work, we applied two different recession analysis methods to 155 catchments in Victoria, Australia. We compared the results from before the drought (1997-2004) to the years 2005-2015, which included the drought period. We also compared catchments which experienced significant changes in their annual rainfall-runoff relationships during the drought to catchments which did not. We found that catchments which experienced significant changes in rainfall-runoff relationships during the Millennium drought also showed significantly steeper recessions. These changes are consistent with decreased connectivity between catchment surface water and subsurface storage, and increased losses of water through the streambed. While increases in evaporation are likely responsible for some of the changes observed, the lack of significant changes in catchments which did not experience changes in rainfall-runoff relationships suggests that changes in subsurface storage dynamics are the main driver of these changes in behaviour.

The research is significant for several reasons. Firstly, it provides valuable insights into how persistent drought conditions can affect catchment storage, which is crucial for water management strategies. Secondly, it is the first study to examine non-stationarity, or changes in behaviour over time, through the lens of recession analysis. This approach could be useful in understanding and predicting hydrological changes in the face of a changing climate. The findings of this piece of research also highlight that the biggest drought-induced distruptions in streamflow and storage dynamics occur during low-flow periods, this has important implications for the sustainable management of riparian ecosystems, which are significantly impacted by changes to low-flow dynamics. In this context, understanding how long, persistent drought affects catchment hydrology can help in developing more effective water management strategies. The study also demonstrates the usefulness of analysing changes in recession behaviour over time to characterise non-stationary hydrological behaviour, providing valuable insights into the role of catchment storage in response to climate change.

A paper describing this research is currently in preparation, and will be available here soon.