When rivers change their tune: unraveling streamflow regime shift after multi-year droughts in south-eastern Australia

Prolonged droughts have led to impacts on streamflow by strongly reducing flows, and in some cases gives rise to permanent shifts in streamflow regimes, despite rainfall recovery. Understanding changes from perennial to non-perennial regimes is crucial for water management, such as the allocation of available water for crop irrigation to environmental flows. Furthermore, given the prospect of a drier and warmer future, to combat increasing water scarcity and environmental degradation, understanding regime changes will help decision makers develop water-related mitigation and adaptation strategies.

In this study we investigate streamflow regime change from perennial to non-perennial flow, combining well established metrics using both climatic and hydrologic indices.  A case study of the Victorian region in south-eastern Australia will be presented applying our analysis to pre-, during and post Millennium drought conditions. We analysed streamflow from 116 Hydrological Reference Sites in Victoria and period from 1970-2019 with respect to changes in the magnitude, duration, frequency, and timing of flow conditions.  In this region, we identified rivers which remained in the non-perennial regime despite rainfall totals returning to pre drought levels. Additionally, we explored attributing for the permanent streamflow regime shift and implications for water management including interacting changes to observed rainfall intensities, vegetation responses and modelled surface and sub-surface components.