Multi-year drought impacts on streamflow regimes

Abstract:       With its highly variable climate, Australia is naturally susceptible to multi-year droughts. Previous studies have shown that Australia will, in future, experience longer and more severe droughts, especially across southern Australia. Extended periods of drought have been associated with hydrological changes, in particular streamflow  regimes including changes to the magnitude, frequency, duration, predictability or flashiness of streamflow (Kiem et al. 2016). Despite significantly impacting water availability across the world, links between multi-year drought effects on the hydrological responses of catchments and changing flow regimes are not well understood. This is an important issue since regime shifts from e.g., perennial to non-perennial, could be correlated to the variability in rainfall intensity and frequency, leading to changes in infiltration, excess overland flow and surface-subsurface connectivity.

Our study aims to assess the effect of multi-year droughts on the streamflow regimes to inform future water resource management. We classify historical and current dominant streamflow regimes across Australia and explore whether the susceptibility of stream networks to perennialism under multi-year drought periods is likely to increase in the future. We first use Victoria as a case study region to improve collective knowledge on non-perennial rivers; their drivers, flow regime patterns and frequency of occurrence using the Australian Bureau of Meteorology (BoM)'s long-term hydrologic reference stations and a range of streamflow-based indicators. We analyse pre-drought states of streamflow regimes and explore whether they have shifted after the Millennium multi-year drought. We also investigate the major climatological and hydrological drivers that affect streamflow regime shifts, with a particular focus on those catchments which have shown to have shifted rainfall-runoff relationships resulting from the Millennium drought.

References

Kiem, A. S., and Coauthors, 2016: Natural hazards in Australia: droughts. Clim. Change, 139, 37–54.