Reed, D.W. 2015b. Naughty thoughts about drought rarity. Proc. HWRS2015 Conference, Hobart, Australia, 8-10 December 2015, Paper 06, 8pp.
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Drought rarity assessment from monthly rainfall data is suspect. Estimates are typically cherry-picked, with raingauge, starting month and duration chosen to maximise the inferred rarity of the drought that a Water Company is experiencing. Yet the water-resource system is sensitive to a spectrum of droughts: not just one of this specific duration and starting month. The paper forms part of a new approach to assessing and visualising the rarity of an ongoing drought based on long-term monthly rainfall records and characteristics of the resource system. Using records from 38 sites across Great Britain and Ireland, it is shown that even a century of data provides only a very small sample of long-duration extremes. Measures related to 98% reliable yield and inter-site dependence are investigated.