When Streams Don’t Recover: Drought driven threats to our water security

It was great to have Associate Professor, Tim Peterson from Monash University join us for this webinar.  Tim shared research findings from previous years which demonstrated how annual and seasonal catchment runoff has recently been shown to shift states during droughts and often it does not recover, resulting in less runoff per unit rainfall than prior to the drought.

Importantly, evidence suggests that the non-recovered catchments appear to be persisting within an alternate runoff state, rather than just being slow to recover. One-third of Victoria’s gauged unregulated catchments have not recovered 12 years after the Millenium drought, resulting in an average of 37% less streamflow per unit rainfall.

Overall, these findings suggest water security is significantly overestimated and that catchments can have a finite resilience to disturbances.

The biophysical causes of these multiple catchment states and the switching between them does, however, remain an open question. Many hypotheses have been proposed that explain the observed changes to catchment water balance; most notably changes in plant water use, recharge and maybe groundwater-surface water interactions.

Tim outlined additional emerging evidence of catchment non-recovery and spent time reviewing the latest leading hypotheses. He also presented a conceptual framework on the role of climate variability which is driving shifts into and out of low runoff states.