On the existence of multiple states of low flows in catchments in southeast Australia

This study investigates whether low flow events in a catchment exhibit a possibility of switching regimes. If this happens, it can result in a catchment experiencing a flow anomaly that is even more extreme than what was historically considered a conventional low flow event. A Hidden Markov Modelling approach was used to identify shifts in the intensity of low flow events in catchments in southeast Australia. We found very strong evidence of low flow intensity exhibiting two distinct states (viz., a normal and an intensified state) for several catchments, providing convincing reasons to believe that low flows can and have undergone regime changes. The periods when the catchments exist in an intensified low flow state were associated with higher maximum and average monthly temperature (Δ≈+2.1,+1°C, respectively) and lower precipitation (Δ≈−25mm, a decline of 30%) compared to periods when these exist in their normal state.