Climate change risks to mine closure

Robust planning for mine closure is crucial for minimising negative environmental impacts and ensuring a positive post-mining legacy. Even though climate is an important factor in the design and management of most post-mine landscape features, general understanding of the multi-facetted nature of climate change risks to mine closure outcomes is limited. An approach is presented to mapping the climate change risk while elucidating the nature of its uncertainty. The approach is demonstrated using five mine closure planning and design considerations, namely: pit lake hydrology, landform stability, flooding, revegetation, and acid and metalliferous drainage. The risk to each of these considerations is quantified with a representative climate index, namely: aridity index, rainfall erosivity, annual maximum 1-day precipitation, extreme drought frequency, and drying period duration. Change in climate indices are derived relative to baseline conditions for two future 30-year periods (2040-2069, and 2070-2099) from an 11-member ensemble of dynamically downscaled simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) for two emission scenarios (Representative Concentration Pathways 4.5 and 8.5). The approach is demonstrated for mines within Queensland, Australia, with future change and uncertainty in indices mapped spatially. Results show that annual maximum 1-day precipitation and extreme drought frequency is expected to become more extreme into the future irrespective of future time period, emission scenario or geographic region; whilst the expected direction of change varies spatially for the aridity index, rainfall erosivity and drying period duration. Most indices suggest that the greatest changes will occur in the Mount Isa mining region, whereas the Weipa mining region projections are highly uncertain. The research demonstrates the multiple facets of climate change risks that need consideration in mine closure planning and design. It provides new insights into the variabilities among indices, across mining regions, over ensemble members and between time horizons that need to be factored in by mine closure stakeholders.