Using tree-rings to inform the reliability of hydropower generation for Australia

Abstract:

A key component of climate change mitigation is transformation of energy systems through widespread uptake of renewables. In Australia, the State of Tasmania is leading this charge, with up to 90% of the State’s energy generated by a hydropower network distributed across six high rainfall catchments. However, concerns over recent declines in inflows for catchments recorded in short instrumental records have raised the question of reliability of flows into the future. Here, we present two new tree-ring based ~1000-year summer inflow reconstructions for Lake Burbury and Lake Rowallan in Tasmania that provide a long term context for recent changes. We then develop a hydrological model (Source) for the two hydro storages to simulate the daily balance of surface water and analyse water levels, spills and extraction rates over the last millennium.

The reconstructions highlight a significant extended pluvial at the start of the reconstruction period that exceeds any in the instrumental period, and a significant period of reduced summer flows during the 1500s similar to that in the recent instrumental record. Modelling daily water balances demonstrates that a) the recent decline in flows and associated storage levels is not unprecedented, b) periods of lower flows than observed in the instrumental record are possible and c) periods of higher inflows and therefore increased extractions/spills are also possible. This extension of the instrumental record places recent trends in water availability in context and allows for a better assessment of the likelihood of extreme events. This information can assist water authorities adjust water management plans such that vulnerability of Australian towns and cities to drought is decreased. Dendroclimatology has an important role to play in reducing uncertainty around flow reliability and there is clear potential for further work in this applied area of research.